8 Basic and Practical Classic Examples in C Language [Source Code Included]

2026-06-10

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1. Output the 9*9 multiplication table. There are 9 rows and 9 columns, with i controlling the rows and j controlling the columns.

//
// Created by 冲哥.
//
#include "stdio.h"

int main() {
    int i, j, result;

    for (i = 1; i < 10; i++) {
        for (j = 1; j <= i; j++) {
            result = i * j;
            printf("%d*%d=%-4d", i, j, result);
        }
        printf("\n");
    }
    return 0;
}

2. Classical Problem: A pair of rabbits, starting from the third month after birth, each month they produce a pair of rabbits. The young rabbits, after reaching the third month, also produce a pair of rabbits each month. If the rabbits do not die, what is the total number of rabbits each month?

//
// Created by 冲哥.
//
#include "stdio.h"

int main() {

    long f1, f2;
    int i;
    f1 = f2 = 1;

    for (i = 1; i <= 20; i++) {
        printf("%12ld %12ld", f1, f2);

        if (i % 2 == 0) printf("\n");/* Control output, four per line */

        f1 = f1 + f2; /* Assign the sum of the previous two months to the third month */

        f2 = f1 + f2; /* Assign the sum of the previous two months to the third month */
    }
    return 0;
}

3. Determine how many prime numbers are there between 101 and 200, and output all prime numbers and their count.

Program analysis: The method to determine a prime number: divide a number by all integers from 2 to sqrt(this number). If it can be divided evenly, then this number is not a prime number; otherwise, it is a prime number.

//
// Created by 冲哥.
//
#include "stdio.h"
#include "math.h"

int main() {

    int m, i, k, h = 0, leap = 1;
    printf("\n");

    for (m = 101; m <= 200; m++) {
        k = sqrt(m + 1);
        for (i = 2; i <= k; i++)
            if (m % i == 0) {
                leap = 0;
                break;
            }
        if (leap) /* If leap remains 1 after the inner loop ends, then m is a prime number */
        {
            printf("%-4d", m);
            h++;
            if (h % 10 == 0)
                printf("\n");
        }
        leap = 1;
    }
    printf("\nThe total is %d", h);
    return 0;
}

4. A number is called a “perfect number” if it is equal to the sum of its factors. For example, 6 = 1 + 2 + 3. Write a program to find all perfect numbers within 1000.

//
// Created by 冲哥.
//
#include "stdio.h"

int main() {
    static int k[10];
    int i, j, n, s;
    for (j = 2; j < 1000; j++) {
        n = -1;
        s = j;
        for (i = 1; i < j; i++) {
            if ((j % i) == 0) {
                n++;
                s = s - i;
                k[n] = i;
            }
        }
        if (s == 0) {
            printf("%d is a perfect number: ", j);
            for (i = 0; i < n; i++)
                printf("%d,", k[i]);
            printf("%d\n", k[n]);
        }
    }
    return 0;
}

5. Program to print a right-angled Pascal’s triangle

//
// Created by 冲哥.
//
#include "stdio.h"

int main() {
    int i, j, a[6][6];

    for (i = 0; i <= 5; i++) {
        a[i][i] = 1;
        a[i][0] = 1;
    }

    for (i = 2; i <= 5; i++)

        for (j = 1; j <= i - 1; j++)

            a[i][j] = a[i - 1][j] + a[i - 1][j - 1];

    for (i = 0; i <= 5; i++) {
        for (j = 0; j <= i; j++)

            printf("%4d", a[i][j]);

        printf("\n");
    }
    return 0;
}

6. Reverse the input string and output it

//
// Created by 冲哥.
//
#include "stdio.h"
#include <string.h>

int main() {
    char c[200], c1;
    int i, j, k;
    printf("Enter a string: ");
    scanf("%s", c);
    k = strlen(c);

    for (i = 0, j = k - 1; i < k / 2; i++, j--) {
        c1 = c[i];
        c[i] = c[j];
        c[j] = c1;
    }
    printf("%s\n", c);
    return 0;
}

7. Find a substring s2 in a string s1, if it exists, return the starting position of the substring in the main string, otherwise return -1.

//
// Created by 冲哥.
//
#include "stdio.h"
#include <string.h>

int main() {
    char s1[6] = "thisis";
    char s2[5] = "is";

    printf("%d\n", search(s1, s2));
    return 0;
}

int search(char s1[], char s2[]) {
    int i = 0, j, len = strlen(s2);

    while (s1[i]) {
        for (j = 0; j < len; j++)
            if (s1[i + j] != s2[j]) break;
        if (j >= len)return i;
        else i++;
    }
    return -1;
}

8. Input a string and determine whether it is a palindrome. A palindrome is a string that reads the same forwards and backwards.

//
// Created by 冲哥.
//
#include <stdio.h>
#include <string.h>
#include<string.h>

int main() {
    char s[100];
    int i, j, n;

    printf("Enter a string:\n");
    gets(s);
    n = strlen(s);
    for (i = 0, j = n - 1; i < j; i++, j--)
        if (s[i] != s[j]) break;
    if (i >= j) printf("It is a palindrome\n");

    else printf("It is not a palindrome\n");
    return 0;
}

9. Use pointer variables to output elements of a structure array.

//
// Created by 冲哥.
//
#include <stdio.h>

struct student {
    int num; // Student ID
    char *name; // Name
    char sex; // Gender
    int age; // Age

} stu[5] = {{1001, "张三",    'F', 18},
            {1002, "李四",  'M', 28},
            {1003, "王五",  'F', 34},
            {1004, "赵六", 'F', 25},
            {1005, "前七", 'M', 19}};

int main() {
    int i;
    struct student *ps;
    printf("Num \tName\t\t\tSex\tAge\t\n");

    // Use pointer variables to output elements of the structure array.
    for (ps = stu; ps < stu + 5; ps++)
        printf("%d\t%-10s\t\t%c\t%d\t\n", ps->num, ps->name, ps->sex, ps->age);
    printf("************************************\n");
    // Use array subscript method to output student ID and age of the structure array elements.
    for (i = 0; i < 5; i++)
        printf("%d\t%d\t\n", stu[i].num, stu[i].age);
    return 0;
}

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