Of course, here are your C language files organized into a structured Markdown notebook. The code snippets have been categorized based on the primary programming concepts they demonstrate.

C Language Programming Notebook#

This document contains a collection of C code examples, categorized by programming concepts, ranging from basic I/O to more complex topics like functions, arrays, and pointers.

1. Basic I/O & Data Types#

Examples focusing on fundamental input/output operations and basic data type manipulations.

1.1. Sum of Character ASCII Values#

This program reads three characters from the input, converts them to their integer ASCII values, and prints the sum.

Source File: Main (1).c

1
#include<stdio.h>
2

3
int main(){
4
 char a,b,c;
5
 scanf("%c%c%c",&a,&b,&c);
6
 int as_a = a;
7
 int as_b = b;
8
 int as_c = c;
9
 int x = as_a+as_b+as_c ;
10

11
 printf("%d",x);
12
    return 0;
13
}

1.2. Formatted Date Parsing#

This code reads a date in YYYY-MM-DD format and prints the year, month, and day on separate lines.

Source File: Main (2).c

1
#include<stdio.h>
2

3
int main(){
4
    int y,m,d;
5
    scanf("%d-%d-%d",&y,&m,&d);
6
    printf("%d年\n%d月\n%d日\n",y,m,d);
7
    return 0;
8
}

1.3. Uppercase to Lowercase Conversion#

This program reads an uppercase character and converts it to its corresponding lowercase character by adding 32 to its ASCII value.

Source File: Main (3).c

1
#include<stdio.h>
2

3
int main() {
4
    char x;
5
    scanf("%c",&x);
6
    char n = x + 32;
7
    printf("%c",n);
8
    return 0;
9
}

2. Conditional Logic (if-else, switch)#

Code that uses conditional statements to control the program flow.

2.1. Piecewise Function Calculation#

Calculates the value of a function f(x) which has different definitions based on whether x is greater than or equal to zero.

Source File: Main (4).c

1
#include <stdio.h>
2
#include<math.h>
3

4
void compute(float *x);
5

6
int main() {
7
    float x;
8
    float y;
9
    scanf("%f",&x);
10
    if (x>=0) {
11
        y=sqrt(x);
12
    }
13
    else {
14
        y=(x+1)*(x+1)+2*x+1/x;
15
    }
16
    printf("f(x)=%.2f\n",y);
17
}

2.2. Odd/Even Number Transformation#

Reads an integer. If the number is odd, it doubles it. If it’s even, it halves it.

Source File: Main (5).c

1
#include <stdio.h>
2
#include<math.h>
3

4
int main() {
5
    int x;
6
    int y;
7
    scanf("%d",&x);
8
    if (x % 2 !=0) {
9
        y = x*2;
10
    }
11
    else {
12
        y=x/2;
13
    }
14
    printf("%d\n",y);
15
}

2.3. IP Address Validator#

Reads four integers representing an IP address and checks if each part is within the valid range of 0 to 255.

Source File: Main (6).c

1
#include <stdio.h>
2
#include<math.h>
3

4
int main() {
5
    int a,b,c,d;
6

7
    scanf("%d.%d.%d.%d",&a,&b,&c,&d);
8
    if ((a>= 0 &&a<= 255)&&(b>= 0 &&b<= 255)&&(c>= 0 &&c<= 255)&&(d>= 0 &&d<= 255)) {
9
        printf("有效");
10
    }
11
    else {
12
        printf("无效");
13
    }
14
    return 0;
15
}

2.4. Greeting Selector (switch-case)#

Displays a different greeting based on the integer input (1 for morning, 2 for afternoon, 3 for night).

Source File: Main (7).c

1
#include <stdio.h>
2

3
int main() {
4
    int x;
5
    scanf("%d",&x);
6
    switch (x) {
7
        case 1: {
8
            printf("Good morning!");
9
            break;
10
        }
11
        case 2: {
12
            printf("Good afternoon!");
13
            break;
14
        }
15
        case 3: {
16
            printf("Good night!");
17
            break;
18
        }
19
        default:printf("input error!");
20
    }
21
    return 0;
22
}

2.5. Character Type Identifier#

Identifies whether the input character is an uppercase letter, lowercase letter, numeric character, or another type of character.

Source File: Main (8).c

1
#include <stdio.h>
2

3
int main() {
4
    char ch;
5
    ch = getchar();
6

7
    if (ch >= 'A' && ch <= 'Z') {
8
        printf("It's a uppercase letter.");
9
    } else if (ch >= 'a' && ch <= 'z') {
10
        printf("It's a lowercase letter.");
11
    } else if (ch >= '0' && ch <= '9') {
12
        printf("It's a numeric character.");
13
    } else {
14
        printf("It's a other character.");
15
    }
16

17
    return 0;
18
}

2.6. Simple Calculator#

Performs addition, subtraction, multiplication, or division based on the operator character entered between two numbers. Includes error handling for division by zero.

Source File: Main (9).c

1
#include<stdio.h>
2

3
int main() {
4
    float a,b,x;
5
    char c;
6
    scanf("%f%c%f",&a,&c,&b);
7
    if(c=='+') {
8
        x=a+b;
9
        printf("%.2f%c%.2f=%.2f",a,c,b,x);
10
    }
11
    else if(c=='-') {
12
        x=a-b;
13
        printf("%.2f%c%.2f=%.2f",a,c,b,x);
14
    }
15
    else if(c=='*') {
16
        x=a*b;
17
        printf("%.2f%c%.2f=%.2f",a,c,b,x);
18
    }
19
    else if(c=='/' && b!=0) {
20
        x=a/b;
21
        printf("%.2f%c%.2f=%.2f",a,c,b,x);
22
    }
23
    else if(c=='/' && b == 0) {
24
        printf("input error!");
25
    }
26
    else {
27
        printf("input error!");
28
    }
29
    return 0;
30
}

2.7. Tiered Electricity Bill Calculator#

Calculates an electricity bill based on a tiered rate system. The cost per unit increases as consumption crosses certain thresholds.

Source File: Main (11).c

1
#include<stdio.h>
2

3
int main(){
4
    int x;
5
    float m = 0;
6
    scanf("%d",&x);
7
    if (x >= 0 && x <= 200){
8
        m = x*0.5;
9
        printf("charge:%.2f",m);
10
    }
11
    else if (x >= 201 && x <= 400){
12
        m = 100+(x-200)*0.65;
13
        printf("charge:%.2f",m);
14
    }
15
    else if (x >= 401 && x <= 600){
16
        m = 230+(x-400)*0.8;
17
        printf("charge:%.2f",m);
18
    }
19
    else if (x >= 601){
20
        m = 390+(x-600)*1.0;
21
        printf("charge:%.2f",m);
22
    }
23
    else if (x<0){
24
        printf("input error!");
25
    }
26
    return 0;
27
}

3. Loops (for, while)#

Programs that utilize loops for repetition, iteration, and pattern generation.

3.1. Integer Reversal#

This program reads an integer and prints its digits in reverse order.

Source File: Main.c

1
#include<stdio.h>
2

3
int main(){
4
    int num;
5
    int temp;
6
    int rev = 0;
7
    scanf("%d",&num);
8
    while(num !=0){
9
        temp = num % 10;
10
        num = num / 10;
11
        rev = rev * 10 + temp;
12
    }
13
    printf("%d",rev);
14
    return 0;
15
}

3.2. Fibonacci Sequence Generator#

Generates and prints the first n numbers of the Fibonacci sequence.

Source File: Main (14).c

1
#include<stdio.h>
2

3
int main() {
4
  int i = 1;
5
  int j = 1;
6
  int sum = 1;
7
  int n;
8
  scanf("%d", &n);
9
  if (n >= 1) {
10
    printf("%d", i);
11
  }
12
  if (n >= 2) {
13
    printf("% d", j);
14
  }
15
  for (int m = 3; m <= n; m++) {
16
    sum = j + i;
17
    printf(" %d", sum);
18
    i = j;
19
    j = sum;
20
  }
21
  return 0;
22
}

3.3. Parallelogram of Stars#

Uses nested loops to print a parallelogram of stars with n rows and m columns.

Source File: Main (17).c

1
#include <stdio.h>
2
int main() {
3
    int n,m;
4
    scanf("%d%d", &n,&m);
5

6
    for(int i = 0; i < n; i++) {  // 控制行数
7
        // 打印空格
8
        for(int j = 0; j < n - i - 1; j++) {
9
            printf(" ");
10
        }
11
        // 打印星号
12
        for(int k = 0; k < m; k++) {
13
            printf("*");
14
        }
15
        printf("\n");  // 换行
16
    }
17
    return 0;
18
}

3.4. Nested Loops for Combinations (Coin Problem)#

Uses three nested loops to find all possible combinations of 10, 5, and 1 unit coins that sum up to a given amount of money.

Source File: Main (20).c

1
#include<stdio.h>
2

3
int main(){
4
    float money;
5
    scanf("%f",&money);
6
    for(int a = 0 ; a <=3;a++){
7
        for(int b = 0; b<= 6;b++){
8
            for(int c = 0; c<=30;c++){
9
                if(a*10 + b*5 + c*1 == 10*money){
10
                    printf("(%d,%d,%d)\n",a,b,c);
11
                }
12
            }
13
        }
14
    }
15
    return 0;
16
}

3.5. Nested Loops for Permutations#

Generates all unique 3-digit numbers that can be formed using the digits n, n+1, n+2, and n+3.

Source File: Main (22).c

1
#include<stdio.h>
2

3
int main(){
4
    int n;
5
    int count = 0;
6
    scanf("%d",&n);
7
    for(int a = n; a<=n+3;a++){
8
        for(int b = n; b<=n+3;b++){
9
            for(int c = n; c<=n+3;c++){
10
                if(a != b && a != c && b != c){
11
                printf("%d%d%d ",a,b,c);
12
                count++;
13
                }
14
            }
15
        }
16
    }
17
    printf("\ncount=%d",count);
18
    return 0;
19
}

3.6. Nested Loops for Equation Solver#

Finds integer solutions (between 1 and 20) for the linear equation ax + by + cz = 20.

Source File: Main (23).c

1
#include<stdio.h>
2

3
int main(){
4
    int a,b,c;
5
    scanf("%d%d%d",&a,&b,&c);
6
    for(int x = 1; x<=20;x++){
7
        for(int y = 1; y<=20;y++){
8
            for(int z = 1; z<=20;z++){
9
                if(a*x+b*y+c*z == 20){
10
                printf("x,y,z: %d,%d,%d\n",x,y,z);
11
                }
12
            }
13
        }
14
    }
15
    return 0;
16
}

4. Mathematical Algorithms#

Implementations of various mathematical calculations and series.

4.1. Sum of a Fraction Series#

Calculates the sum of the first n terms of the series: 1/2 + 2/3 + 3/5 + 5/8 + …

Source File: Main (10).c

1
#include <stdio.h>
2

3
int main() {
4
    int n;
5
    scanf("%d", &n);
6

7
    if (n <= 0) {
8
        printf("input error!\n");
9
        return 0;
10
    }
11

12
    float sum = 0.0f;
13
    int numerator = 1, denominator = 2;
14

15
    for (int i = 0; i < n; i++) {
16
        sum += (float)numerator / denominator;
17

18
        // 更新分子和分母
19
        int next_numerator = denominator;
20
        int next_denominator = numerator + denominator;
21

22
        numerator = next_numerator;
23
        denominator = next_denominator;
24
    }
25

26
    printf("sum=%.2f\n", sum);
27
    return 0;
28
}

4.2. Approximation of ‘e’#

Approximates the value of the mathematical constant ‘e’ by summing the first n terms of the series: 1 + 1/1! + 1/2! + 1/3! + …

Source File: Main (12).c

1
#include <stdio.h>
2

3
int main() {
4
    int n;
5
    scanf("%d", &n);
6

7
    if (n <= 0) {
8
        printf("input error!\n");
9
        return 0;
10
    }
11

12
    double e = 1.0;     // 初始值为1
13
    double factorial = 1.0; // 用于计算阶乘
14

15
    for (int i = 1; i < n; i++) {
16
        factorial *= i;            // 计算i的阶乘
17
        e += 1.0 / factorial;     // 加上当前项
18
    }
19

20
    printf("%.12lf\n", e);
21
    return 0;
22
}

4.3. GCD & LCM#

Calculates the Greatest Common Divisor (GCD) and Least Common Multiple (LCM) of two integers using the Euclidean algorithm.

Source File: Main (13).c

1
#include <stdio.h>
2

3
int main() {
4
    int m, n;
5
    scanf("%d %d", &m, &n);
6

7
    // 计算 GCD（辗转相除法）
8
    int a = m, b = n;
9

10
    while (b != 0) {
11
        int temp = b;
12
        b = a % b;
13
        a = temp;
14
    }
15
    int gcd = a;
16

17
    // 计算 LCM
18
    int lcm = (m / gcd) * n;  // 防止 m * n 溢出
19

20
    // 输出结果
21
    printf("the greatest common divisor:%d\n", gcd);
22
    printf("the minimum common multiple:%d\n", lcm);
23

24
    return 0;
25
}

4.4. Sum of `a + aa + aaa + ...` Series#

Calculates the sum of the series a + aa + aaa + ... for n terms. For example, if a=2 and n=3, it calculates 2 + 22 + 222.

Source File: Main (18).c

1
#include <stdio.h>
2

3
int main() {
4
    int a, n;
5
    long long sum = 0;
6
    long long term = 0;
7

8
    scanf("%d %d", &a, &n);
9

10
    for (int i = 0; i < n; i++) {
11
        term = term * 10 + a;
12
        sum += term;
13
    }
14

15
    printf("%lld\n", sum);
16

17
    return 0;
18
}

4.5. Harmonic and Alternating Series Sum#

For three given integer inputs (n), this code calculates the sum of the harmonic series (1 + 1/2 + 1/3 + … + 1/n) and the alternating harmonic series (1 - 1/2 + 1/3 - …).

Source File: Main (19).c

1
#include <stdio.h>
2

3
int main() {
4
    int n_values[3];
5
    float x_sums[3];
6
    float y_sums[3];
7
    int i, j;
8

9
    scanf("%d %d %d", &n_values[0], &n_values[1], &n_values[2]);
10

11
    for (j = 0; j < 3; j++) {
12
        int n = n_values[j];
13
        float current_x_sum = 0.0L;
14
        float current_y_sum = 0.0L;
15

16
        for (i = 1; i <= n; i++) {
17
            float term = 1.0L / (float)i;
18
            current_x_sum += term;
19
            if (i % 2 == 1) {
20
                current_y_sum += term;
21
            } else {
22
                current_y_sum -= term;
23
            }
24
        }
25
        x_sums[j] = current_x_sum;
26
        y_sums[j] = current_y_sum;
27
    }
28

29
    printf("x序列的和分别为：%.5f %.5f %.5f\n", x_sums[0], x_sums[1], x_sums[2]);
30
    printf("y序列的和分别为：%.5f %.5f %.5f\n", y_sums[0], y_sums[1], y_sums[2]);
31

32
    return 0;
33
}

5. Arrays#

Examples involving data storage and manipulation using one-dimensional and two-dimensional arrays.

5.1. One-Dimensional Arrays#

5.1.1. Replace Negative Numbers with Zero#

Reads n integers into an array and replaces any negative numbers with 0 before printing the result.

Source File: Main.cpp

1
#include <stdio.h>
2
int main()
3
{
4
    int n,i;
5
    scanf("%d",&n);
6
    int a[n];
7

8
    for(i=0;i<n;i++)
9
    {
10
        int *p = &a[i];
11
        scanf("%d", p);
12

13
        if(*p<0) {
14
            *p=0;
15
        }
16
        a[i]=*p;
17
    }
18

19
    for(int j=0;j<n;j++) {
20
        printf("%d ", a[j]);
21
    }
22
    return 0;
23
}

5.1.2. Array Reversal#

Reverses the elements of a 10-element integer array in-place.

Source File: main (21).c

1
#include <stdio.h>
2
int main()
3
{
4
   int a[10]={0};
5
   int x;
6
   int temp = 0;
7
   int i;
8
   for(int i = 0;i<10;i++){
9
       scanf("%d",&x);
10
       a[i]=x;
11
   }
12
   for(int j = 0;j<5;j++){
13
       temp=a[j];
14
       a[j]=a[9-j];
15
       a[9-j]=temp;
16
   }
17
   for(i = 0; i<10; i++)
18
        printf("%d ", a[i]);
19
    return 0;
20
}

5.1.3. Deleting an Element from an Array#

Searches for a number in a pre-defined array. If found, it removes the first occurrence by shifting subsequent elements to the left.

Source File: Main (24).c

1
#include<stdio.h>
2

3
int main() {
4
    int arr[10] ={12,45,87,64,15,-47,69,16,63,36};
5
    int num;
6
    int pin = 0;
7
    scanf("%d",&num);
8
    for(int i =0;i<10;i++){
9
        if(arr[i]==num){
10
            pin = 1;
11
            for(int j = i;j<9;j++){
12
                arr[j]=arr[j+1];
13
            }
14
        }
15
    }
16
    if(pin == 1){
17
        for (int i = 0; i < 10; i++) {
18
        printf("%d ", arr[i]);
19
    }
20
    printf("\n");}
21
    else{
22
        printf("Not Found!");
23
    }
24
    return 0;
25
}

5.1.4. Inserting an Element into a Sorted Array#

Inserts a number into a pre-defined sorted array and then re-sorts the array to maintain ascending order using a bubble sort.

Source File: main (25).c

1
#include <stdio.h>
2
int main()
3
{
4
    int a[10]={2,5,6,8,11,15,17,20,25};
5
    int x;
6
    int i=0;
7
    int temp = 0;
8
    int n = 10;
9
    int m = 0;
10
    scanf("%d",&m);
11
    a[9]=m;
12
    for(x = 0;x<10;x++){
13
        for (int y = 0 ; y< 9 - x;y++){
14
        if(a[y]>a[y+1]){
15
            temp = a[y];
16
            a[y]=a[y+1];
17
            a[y+1]=temp;
18
        }
19
    }
20
    }
21

22
   for(i = 0; i<n; i++)
23
        printf("%d ", a[i]);
24
    return 0;
25
}

5.1.5. Finding the Most Frequent Element#

Finds the number that appears most frequently in an array of 12 integers and prints the number and its frequency.

Source File: Main (27).c

1
#include <stdio.h>
2

3
int main() {
4
    int a[12];
5
  int current_count = 0;
6
  int max_times =0;
7
  int most_number=0;
8
  for (int i = 0; i < 12; i++) {
9
    scanf("%d", &a[i]);
10
  }
11
  for(int i = 0;i<12;i++){
12
    current_count = 0;
13
    for(int j =0;j<=12;j++){
14
      if(a[j]==a[i]){
15
        current_count++;
16
      }
17
    }
18
    if(current_count > max_times){
19
      max_times = current_count;
20
      most_number = a[i];
21
    }
22
  }
23

24
  printf("num: %d, times=%d\n", most_number, max_times);
25
}

5.1.6. Partitioning an Array#

Rearranges an array such that all elements less than a given number n come first, followed by elements equal to n, and finally elements greater than n.

Source File: main (30).c```c #include <stdio.h> int main() { int a[10] = {3,6,1,0,5,2,7,8,3,4}; int n, i; int flag = 0; int result[10];

1
scanf("%d", &n);
2

3
for(i = 0; i < 10; i++) {
4
    if(a[i] == n) {
5
        flag = 1;
6
        break;
7
    }
8
}
9

10
if(flag) {
11
    int left = 0;
12

13
    for(i = 0; i < 10; i++) {
14
        if(a[i] < n) {
15
            result[left++] = a[i];
16
        }
17
    }
18

19
    for(i = 0; i < 10; i++) {
20
        if(a[i] == n) {
21
            result[left++] = a[i];
22
        }
23
    }
24

25
    for(i = 0; i < 10; i++) {
26
        if(a[i] > n) {
27
            result[left++] = a[i];
28
        }
29
    }
30

31
    for(i = 0; i < 10; i++) {
32
        a[i] = result[i];
33
    }
34
}

if(flag) for(i = 0; i<10; i++) printf(“%d ”, a[i]); else printf(“Wrong number!”); return 0; }

1
### 5.2. Two-Dimensional Arrays
2

3
#### 5.2.1. Finding Maximum Value per Column
4
Reads a 3x4 matrix and finds the maximum value in each of its four columns.
5

6
*Source File: `Main (26).c`*
7
```c
8
#include <stdio.h>
9

10
int main() {
11
    int arr[3][4];
12
    for (int i = 0; i < 3; i++) {
13
        for (int j = 0; j < 4; j++) {
14
            scanf("%d", &arr[i][j]);
15
        }
16
    }
17
    for (int j = 0; j < 4; j++) {
18
        int max = arr[0][j];
19
        for (int i = 0; i < 3; i++) {
20
            if (max < arr[i][j]) {
21
                max = arr[i][j];
22
            }
23
        }
24
        printf("max[%d]=%d\n",j,max);
25
    }
26
}

5.2.2. Finding Maximum Value per Row#

Reads a 4x4 matrix and finds the maximum value in each of its four rows.

Source File: Main (47).c

1
#include<stdio.h>
2

3
int main() {
4
    int a[4][4] = {0};
5
    for (int i = 0;i<4;i++) {
6
        for (int j = 0;j<4;j++) {
7
            scanf("%d",&a[i][j]);
8
        }
9
    }
10
    int max[4]={0}; // Corrected size from 3 to 4
11
    for (int i = 0;i<4;i++) {
12
        for (int j = 0;j<4;j++) {
13
            if (max[i] < a[i][j]) {
14
                max[i] = a[i][j];
15
            }
16
        }
17
    }
18
    for (int i = 0;i<4;i++) {
19
        printf("%d\n",max[i]);
20
    }
21
    return 0;
22
}

6. Strings#

Code for manipulating character arrays (strings).

6.1. Extracting Date from ID Number#

Reads an 18-digit ID card number as a string and extracts the year and month of birth.

Source File: Main (28).c

1
#include <stdio.h>
2
#include <string.h>
3

4
int main() {
5
    char id_card[19];
6
    int year, month;
7

8
    scanf("%s", id_card);
9

10
    if (strlen(id_card) == 18) {
11
        sscanf(id_card, "%*6s%4d%2d", &year, &month);
12
        printf("%d-%d\n", year, month);
13
    } else {
14
        printf("input error\n");
15
    }
16
    return 0;
17
}

6.2. Sorting an Array of Strings#

Reads four strings and sorts them in alphabetical order using a bubble sort algorithm.

Source File: Main (29).c

1
#include<stdio.h>
2
#include<string.h>
3

4
int main(){
5
    char names[4][200];
6
    char temp[200];
7

8
    for(int i=0;i<4;i++){
9
        scanf("%s",names[i]);
10
    }
11
    for(int i=0;i<3;i++){
12
        for(int j = 0 ;j<3-i;j++){
13
            if(strcmp(names[j],names[j+1]) >0){
14
                strcpy(temp,names[j]);
15
                strcpy(names[j],names[j+1]);
16
                strcpy(names[j+1],temp);
17
            }
18
        }
19
    }
20

21
    for(int i=0;i<4;i++){
22
        printf("%s\n",names[i]);
23
    }
24
}

7. Functions#

Examples that demonstrate breaking down problems into smaller, reusable pieces of code using functions.

7.1. Leap Year Checker#

A function fun(year) that returns 1 if the given year is a leap year, and 0 otherwise.

Source File: main (31).c

1
#include<stdio.h>
2
int fun(int n);
3
int main()
4
{
5
    int year , f ;
6
    scanf("%d",&year);
7
    f=fun(year);
8
    if(f==1)
9
         printf("yes");
10
    else
11
        printf("no");
12
}
13
int fun(int i) {
14
    int m;
15
    if ((i % 4 == 0 && i %100 != 0 )||  i % 400 == 0) {
16
        m = 1;
17
    }
18
    else {
19
        m = 0;
20
    }
21
    return m;
22
}

7.2. Printing a Star Pyramid#

A function prn(n) that prints a pyramid of stars with n rows.

Source File: main (32).c

1
#include<stdio.h>
2
void prn(int n);
3
int main()
4
{
5
   int a;
6
   scanf("%d",&a);
7
   prn(a);
8
   return 0;
9
 }
10
void prn(int n) {
11
    for (int i = 1; i <= n; i++) {
12
        for (int j = n; j > i; j--) {
13
            printf(" ");
14
        }
15
        for (int k = 1; k <= 2*i-1; k++) {
16
            if ((k & 1) == 1)
17
                printf("*");
18
            else
19
                printf(" ");
20
        }
21
        printf("\n");
22
    }
23
}

7.3. Prime Number Checker#

A function prm(n) that checks if a number is prime. The main function then prints all prime numbers up to a given limit m.

Source File: main (33).c

1
#include <stdio.h>
2

3
int prm(int n);
4
int main()
5
{
6
   int i,m;
7
   scanf("%d",&m);
8
   for(i=0;i<=m;i++)
9
   {
10
    if(prm(i)==1) printf("%d ",i);}
11
   return 0;
12
 }
13
int prm(int n) {
14
    int p = 1;
15
    if (n==0 || n ==1) {
16
        p=0;
17
    }
18
    for (int j=2;j<n;j++) {
19
        if (n%j==0) {
20
            p=0;
21
            break;
22
        }
23
    }
24
    return p;
25
}

7.4. Finding Numbers with a Specific Divisor Sum#

Finds all numbers i up to m where the sum of i’s proper divisors equals n.

Source File: Main (16).c

1
#include<stdio.h>
2

3
int sushu(int m); // Note: Function name 'sushu' means 'prime', but it calculates sum of divisors.
4
int main() {
5
    int m,n;
6
    int count = 0;
7
    scanf("%d%d", &m,&n);
8

9
    for (int i = 1; i <= m; i++) {
10
        if (sushu(i)==n) {
11
            printf("%d ",i);
12
            count = 1;
13
        }
14
    }
15
    if (count == 0) {
16
        printf("no such numbers");
17
    }
18
}
19

20
int sushu(int m) {
21
    int sum=0;
22
    for (int j = 2; j < m;j++) {
23
        if (m % j == 0) {
24
            sum+=j;
25
        }
26
    }
27
    return sum;
28
}

7.5. Finding and Summing Factors#

A function fac(n) that prints all factors of a number n and returns their sum.

Source File: main (35).c

1
#include<stdio.h>
2
int fac(int n);
3
int main()
4
{
5
    int n;
6
    scanf("%d",&n);
7
    printf("因子：");
8
    printf("\n因子和：%d",fac(n));
9
    return 0;
10
}
11
int fac(int n) {
12
    int count=0;
13
    for (int i =1;i<=n;i++) {
14
        if (n%i == 0) {
15
            printf("%d ",i);
16
            count+=i;
17
        }
18
    }
19
    return count;
20
}

7.6. Integer Power Calculation#

A function powr(m, n) that calculates m raised to the power of n.

Source File: main (36).c```c #include<stdio.h> #include<math.h> double powr(int m,int n); int main() { int m, n; scanf(“%d%d”, &m, &n); printf(“%.0lf\n”, powr(m,n)); return 0; } double powr(int m,int n) { int answer=1; for (int i = 1;i<=n;i++) { answer *= m; } return answer; }

1
### 7.7. Recursive Sequence (Fibonacci-style)
2
A function `f(n)` that calculates the n-th term of the sequence defined by `a[1]=1`, `a[2]=2`, and `a[i] = a[i-1] + a[i-2]`.
3

4
*Source File: `main (37).c`*
5
```c
6
#include <stdio.h>
7

8
int f(int n);
9
int main()
10
{
11
   int n;
12
   scanf("%d",&n);
13
   printf("%d",f(n));
14
   return 0;
15
 }
16
int f(int n) {
17
    int a[100] = {0};
18
    a[1] = 1;
19
    a[2] = 2;
20

21
    for (int i =3;i<=n;i++) {
22
        a[i]= a[i-2]+a[i-1];
23
    }
24
    return a[n];
25
}

7.8. Armstrong Number Finder#

A function fun(x) that checks if a 3-digit number is an Armstrong number (the sum of the cubes of its digits equals the number itself).

Source File: main (38).c

1
#include<stdio.h>
2
int fun(int x);
3
int main()
4
{ int m,n,i;
5
  scanf("%d",&n);
6
  for(i=n;i<=999;i++)
7
    {
8
        m=fun(i);
9
        if(m==1)
10
            printf("%d ",i);
11
    }
12
}
13
int fun(int x) {
14
    int answer=0;
15
    int a = x /100;
16
    int b = (x % 100)/  10;
17
    int c = x%10;
18
    if (a*a*a + b*b*b + c*c*c == x) {
19
        answer = 1;
20
    }
21
    else {
22
        answer = 0;
23
    }
24
return answer;
25
}

7.9. Matrix Transposition#

A function fun that initializes a 4x4 matrix and then transposes it.

Source File: main (39).c

1
#include<stdio.h>
2
void fun(int a[][4], int n);
3
int main()
4
{  int i,j,n;
5
    int a[4][4];
6
    scanf("%d",&n);
7
    fun(a,n);
8
    for(i=0;i<4;i++)
9
    {
10
        for(j=0;j<4;j++)
11
            printf("%3d",a[i][j]);
12
        printf("\n");
13
    }
14
}
15
void fun(int a[][4], int n) {
16
    int i, j;
17
    int temp[4][4];
18

19
    printf("before:\n");
20

21
    for (i = 0; i < 4; i++) {
22
        for (j = 0; j < 4; j++) {
23
            a[i][j] = n * i + j;
24
            temp[i][j] = a[i][j];
25
            printf("%3d", a[i][j]);
26
        }
27
        printf("\n");
28
    }
29
    printf("after:\n");
30

31
    for (i = 0; i < 4; i++) {
32
        for (j = 0; j < 4; j++) {
33
            a[j][i] = temp[i][j];
34
        }
35
    }
36
}

7.10. Word Counter#

A function words(s[]) that counts the number of words in a given string.

Source File: main (40).c

1
#include<stdio.h>
2
int words(char s[]);
3
int main()
4
{
5
    char s[100];
6
    gets(s);
7
    printf("%d",words(s));
8
}
9
int words(char s[]) {
10
    int count = 0;
11
    int in_word = 0;
12
    int i = 0;
13

14
    while(s[i] != '\0'){
15
        if(s[i] != ' '){
16
            if(in_word == 0){
17
                count ++;
18
                in_word = 1;
19
            }
20
        }
21
        else{
22
            in_word = 0;
23
        }
24
        i++;
25
    }
26
    return count;
27
}

7.11. Password Validator#

A function pws(s[]) that validates a password. It returns 1 (pass) if the password is longer than 6 characters and contains a mix of letters, digits, and special characters. Otherwise, it returns 0 (fail).

Source File: main (42).c

1
#include<stdio.h>
2
#include<string.h>
3
int pws(char s[]);
4
int main()
5
{
6
    char str[50];
7
    int n;
8
    gets(str);
9
    n = pws(str);
10
    if (n==1)
11
        printf ("pass");
12
    else
13
        printf ("fail");
14
    return 0;
15
}
16
int pws(char s[]) {
17
    int len = strlen(s);
18
    if (len <= 6) {
19
        return 0;
20
    }
21

22
    int has_alpha = 0, has_digit = 0, has_special = 0;
23
    for (int i = 0; i < len; i++) {
24
        char c = s[i];
25
        if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) {
26
            has_alpha = 1;
27
        } else if (c >= '0' && c <= '9') {
28
            has_digit = 1;
29
        } else {
30
            has_special = 1;
31
        }
32
    }
33

34
    return (has_alpha && has_digit && has_special);
35
}

7.12. String Concatenation#

A function catstr that appends the contents of one string to the end of another.

Source File: main (48).c

1
#include<stdio.h>
2
#include<string.h>
3
void  catstr(char *a , char  *b)
4
{
5
      int i = 0;
6
      while (a[i] != '\0') {
7
          i++;
8
      }
9
      int j = 0;
10
      while (b[j] != '\0' && i < 19) {
11
          a[i++] = b[j++];
12
      }
13
      a[i] = '\0';
14
}
15
int  main( )
16
{  char  a[20] , b[10];
17

18
       fgets(a, sizeof(a), stdin);
19
       a[strcspn(a, "\n")] = '\0';
20

21
       fgets(b, sizeof(b), stdin);
22
       b[strcspn(b, "\n")] = '\0';
23

24
       catstr(a, b);
25
       printf("%s\n", a);
26
}

8. Pointers#

Code that utilizes pointers for direct memory manipulation, such as passing arguments by reference.

8.1. Swapping Two Integers#

Reads two integers and swaps their values using pointers.

Source File: Main (44).c

1
#include<stdio.h>
2
int main()
3
{
4
    int a, b;
5
    int *pa = &a, *pb = &b;
6
    int temp;
7

8
    scanf("%d%d", pa, pb);
9

10
    temp = *pa;
11
    *pa = *pb;
12
    *pb = temp;
13

14
    printf("%d,%d", *pa, *pb);
15
    return 0;
16
}

8.2. Separating a Double into Integer and Fractional Parts#

A function that takes a double and two pointers. It stores the integer part of the double in the location pointed to by ip and the fractional part in the location pointed to by fp.

Source File: Main (43).c

1
#include<stdio.h>
2
void fun(double x, int *ip, double *fp);
3
int main() {
4
    double i ;
5
    scanf("%lf",&i);
6
    int t;
7
    double f;
8

9
    fun(i,&t,&f);
10
    printf("整数部分：%d，小数部分：%g",t,f);
11
}
12
void fun(double x, int *ip, double *fp){
13
    *ip = x / 1;
14
    *fp = x - *ip;
15
}

8.3. Palindrome Checker with Pointers#

A function fun(char *p) that takes a pointer to a string and checks if it is a palindrome (reads the same forwards and backward).

Source File: Main (45).c

1
#include<stdio.h>
2
#include<string.h>
3
int fun(char *p);
4
int main() {
5
    int a = 1;
6
    char c[100] ;
7
    scanf("%s",c);
8
    a = fun(c);
9
    if (a == 0) {
10
        printf("是回文串");
11
    }
12
    else {
13
        printf("不是回文串");
14
    }
15
    return 0;
16
}
17

18
int fun(char *p) {
19
    int answer = 0;
20
    int lenth = strlen(p);
21
    for (int i = 0;i<=lenth/2;i++) {
22
        if (p[i]!=p[lenth - i-1]) {
23
            answer = 1;
24
            break;
25
        }
26
    }
27
    return answer;
28
}

8.4. Separating a String by Character Type#

A function fun that takes a source string and two destination strings. It iterates through the source and copies all digit characters to the first destination string (s1) and all letter characters to the second (s2).

Source File: Main (46).c

1
#include<stdio.h>
2
#include<string.h>
3
void fun(char *s, char *s1, char *s2);
4
int main() {
5
    char s[100];
6
    char s1[100];
7
    char s2[100];
8
    scanf("%s",s);
9
    fun(s,s1,s2);
10
    return 0;
11
}
12

13
void fun(char *s, char *s1, char *s2) {
14
    int lenth = strlen(s);
15
    int j =0;
16
    int k =0;
17

18
    for (int i =0;i<=lenth;i++) {
19

20
        if (s[i]>= '0' && s[i]<= '9') {
21
            s1[j] = s[i];
22
            j++;
23
        }
24
        if (s[i]>= 'A'  && s[i]<= 'Z') {
25
            s2[k] = s[i];
26
            k++;
27
        }
28
        if (s[i]>= 'a'  && s[i]<= 'z') {
29
            s2[k] = s[i];
30
            k++;
31
        }
32
    }
33
    s1[j] = '\0'; // Null-terminate the strings
34
    s2[k] = '\0';
35
    printf("%s\n", s1);
36
    printf("%s\n", s2);
37
}

わたしの部屋