Loops in C Programming

1for (initialization; condition; update) {
2    // Code to be executed in each iteration
3}

1#include <stdio.h>
2
3int main() {
4    // Print numbers from 1 to 10
5    for (int i = 1; i <= 10; i++) {
6        printf("%d ", i);
7    }
8    printf("\n");
9    
10    return 0;
11}
12
13// Output: 1 2 3 4 5 6 7 8 9 10

1#include <stdio.h>
2
3int main() {
4    int sum = 0;
5    
6    // Calculate sum of numbers from 1 to 100
7    for (int i = 1; i <= 100; i++) {
8        sum += i;
9    }
10    
11    printf("Sum of numbers from 1 to 100: %d\n", sum);
12    
13    return 0;
14}
15
16// Output: Sum of numbers from 1 to 100: 5050

1while (condition) {
2    // Code to be executed as long as condition is true
3}

1#include <stdio.h>
2
3int main() {
4    int number;
5    int sum = 0;
6    
7    printf("Enter positive numbers (enter a negative number to stop):\n");
8    
9    while (1) {  // Infinite loop, will break when condition is met
10        printf("Enter a number: ");
11        scanf("%d", &number);
12        
13        if (number < 0) {
14            break;  // Exit the loop if number is negative
15        }
16        
17        sum += number;
18    }
19    
20    printf("Sum of all positive numbers entered: %d\n", sum);
21    
22    return 0;
23}

1#include <stdio.h>
2
3int main() {
4    int numbers[] = {10, 20, 30, 40, 50};
5    int size = sizeof(numbers) / sizeof(numbers[0]);
6    int i = 0;
7    
8    while (i < size) {
9        printf("%d: %d\n", i, numbers[i]);
10        i++;
11    }
12    
13    return 0;
14}
15
16// Output:
17// 0: 10
18// 1: 20
19// 2: 30
20// 3: 40
21// 4: 50

1do {
2    // Code to be executed at least once
3} while (condition);

1#include <stdio.h>
2
3int main() {
4    int choice;
5    
6    do {
7        printf("\n--- Menu ---\n");
8        printf("1. Option One\n");
9        printf("2. Option Two\n");
10        printf("3. Option Three\n");
11        printf("4. Exit\n");
12        printf("Enter your choice (1-4): ");
13        scanf("%d", &choice);
14        
15        switch (choice) {
16            case 1:
17                printf("You selected Option One\n");
18                break;
19            case 2:
20                printf("You selected Option Two\n");
21                break;
22            case 3:
23                printf("You selected Option Three\n");
24                break;
25            case 4:
26                printf("Exiting program...\n");
27                break;
28            default:
29                printf("Invalid option! Please try again.\n");
30        }
31        
32    } while (choice != 4);
33    
34    return 0;
35}

1#include <stdio.h>
2
3int main() {
4    int number;
5    
6    do {
7        printf("Enter a positive number: ");
8        scanf("%d", &number);
9        
10        if (number <= 0) {
11            printf("Error: Number must be positive.\n");
12        }
13        
14    } while (number <= 0);
15    
16    printf("You entered: %d\n", number);
17    
18    return 0;
19}

1#include <stdio.h>
2
3int main() {
4    int rows = 5;
5    
6    for (int i = 1; i <= rows; i++) {
7        // Inner loop to print stars
8        for (int j = 1; j <= i; j++) {
9            printf("* ");
10        }
11        printf("\n");
12    }
13    
14    return 0;
15}
16
17// Output:
18// * 
19// * * 
20// * * * 
21// * * * * 
22// * * * * *

1#include <stdio.h>
2
3int main() {
4    int matrix[3][3] = {
5        {1, 2, 3},
6        {4, 5, 6},
7        {7, 8, 9}
8    };
9    int sum = 0;
10    
11    // Calculate the sum of all elements in the matrix
12    for (int i = 0; i < 3; i++) {
13        for (int j = 0; j < 3; j++) {
14            sum += matrix[i][j];
15            printf("%d ", matrix[i][j]); // Print each element
16        }
17        printf("\n"); // Move to next row
18    }
19    
20    printf("\nSum of all matrix elements: %d\n", sum);
21    
22    return 0;
23}
24
25// Output:
26// 1 2 3 
27// 4 5 6 
28// 7 8 9 
29// 
30// Sum of all matrix elements: 45

1#include <stdio.h>
2#include <stdlib.h>  // For exit() function
3
4int main() {
5    int num;
6    
7    printf("Enter 0 to exit the program.\n");
8    
9    while (1) {  // Intentional infinite loop
10        printf("Enter a number: ");
11        scanf("%d", &num);
12        
13        if (num == 0) {
14            printf("Exiting program...\n");
15            break;  // Exit condition
16        }
17        
18        printf("You entered: %d\n", num);
19    }
20    
21    return 0;
22}

1#include <stdio.h>
2#include <stdbool.h>
3
4bool isPrime(int num) {
5    if (num <= 1) return false;
6    if (num <= 3) return true;
7    if (num % 2 == 0 || num % 3 == 0) return false;
8    
9    // Check for factors beyond 3
10    for (int i = 5; i * i <= num; i += 6) {
11        if (num % i == 0 || num % (i + 2) == 0) {
12            return false;
13        }
14    }
15    
16    return true;
17}
18
19int main() {
20    int limit;
21    
22    printf("Find prime numbers up to: ");
23    scanf("%d", &limit);
24    
25    printf("Prime numbers up to %d are:\n", limit);
26    
27    for (int i = 2; i <= limit; i++) {
28        if (isPrime(i)) {
29            printf("%d ", i);
30        }
31    }
32    printf("\n");
33    
34    return 0;
35}

1#include <stdio.h>
2
3int main() {
4    int n, first = 0, second = 1, next;
5    
6    printf("Enter the number of Fibonacci terms to generate: ");
7    scanf("%d", &n);
8    
9    printf("Fibonacci Sequence:\n");
10    
11    for (int i = 0; i < n; i++) {
12        if (i <= 1) {
13            next = i;
14        } else {
15            next = first + second;
16            first = second;
17            second = next;
18        }
19        printf("%d ", next);
20    }
21    printf("\n");
22    
23    return 0;
24}