// 2. Calculate the sum of all odd numbers between 1 and 50 using a while loop:

#include <stdio.h>

int main() {
    int sum = 0, i = 1;
    while(i <= 50) {
        if(i % 2 != 0) {
            sum += i;
        }
        i++;
    }
    printf("Sum of all odd numbers between 1 and 50 is: %d\n", sum);
    return 0;
}

// 3. Print the multiplication table of a given number using a for loop:

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);

    for(int i = 1; i <= 10; i++) {
        printf("%d x %d = %d\n", num, i, num * i);
    }
    return 0;
}

// 4. Find the factorial of a given number using a for loop:

#include <stdio.h>

int main() {
    int num, factorial = 1;
    printf("Enter a number: ");
    scanf("%d", &num);

    for(int i = 1; i <= num; i++) {
        factorial *= i;
    }
    printf("Factorial of %d is: %d\n", num, factorial);
    return 0;
}

// 5. Check if a given number is prime or not using a for loop:

#include <stdio.h>

int main() {
    int num, isPrime = 1;
    printf("Enter a number: ");
    scanf("%d", &num);

    if (num <= 1) {
        isPrime = 0;
    } else {
        for(int i = 2; i <= num / 2; i++) {
            if(num % i == 0) {
                isPrime = 0;
                break;
            }
        }
    }

    if(isPrime) {
        printf("%d is a prime number.\n", num);
    } else {
        printf("%d is not a prime number.\n", num);
    }

    return 0;
}

// 6. Print the Fibonacci series up to a given number using a for loop:

#include <stdio.h>

int main() {
    int n, t1 = 0, t2 = 1, nextTerm;

    printf("Enter the number of terms: ");
    scanf("%d", &n);

    printf("Fibonacci Series: %d, %d", t1, t2);

    for(int i = 3; i <= n; i++) {
        nextTerm = t1 + t2;
        printf(", %d", nextTerm);
        t1 = t2;
        t2 = nextTerm;
    }
    printf("\n");
    return 0;
}

// 7. Find the sum of all elements in an array using a for loop:

#include <stdio.h>

int main() {
    int n, sum = 0;

    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements of the array:\n");
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    for(int i = 0; i < n; i++) {
        sum += arr[i];
    }

    printf("Sum of all elements in the array is: %d\n", sum);
    return 0;
}

// 8. Find the largest element in an array using a for loop:

#include <stdio.h>

int main() {
    int n;

    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements of the array:\n");
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    int largest = arr[0];
    for(int i = 1; i < n; i++) {
        if(arr[i] > largest) {
            largest = arr[i];
        }
    }

    printf("The largest element in the array is: %d\n", largest);
    return 0;
}

// 9. Find the smallest element in an array using a for loop:

#include <stdio.h>

int main() {
    int n;

    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements of the array:\n");
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    int smallest = arr[0];
    for(int i = 1; i < n; i++) {
        if(arr[i] < smallest) {
            smallest = arr[i];
        }
    }

    printf("The smallest element in the array is: %d\n", smallest);
    return 0;
}

// 10. Reverse an array using a for loop:

#include <stdio.h>

int main() {
    int n;

    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements of the array:\n");
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    printf("Reversed array:\n");
    for(int i = n-1; i >= 0; i--) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    return 0;
}

// 11. Sort an array in ascending order using a for loop:

#include <stdio.h>

int main() {
    int n;

    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements of the array:\n");
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    for(int i = 0; i < n-1; i++) {
        for(int j = i+1; j < n; j++) {
            if(arr[i] > arr[j]) {
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
    }

    printf("Array in ascending order:\n");
    for(int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    return 0;
}

// 12. Sort an array in descending order using a for loop:

#include <stdio.h>

int main() {
    int n;

    printf("Enter the number of elements in the array: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements of the array:\n");
    for(int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    for(int i = 0; i < n-1; i++) {
        for(int j = i+1; j < n; j++) {
            if(arr[i] < arr[j]) {
                int temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
            }
        }
    }

    printf("Array in descending order:\n");
    for(int i = 0; i < n; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    return 0;
}

// 13. Find the sum of the digits of a given number using a while loop:

#include <stdio.h>

int main() {
    int num, sum = 0;

    printf("Enter a number: ");
    scanf("%d", &num);

    while(num != 0) {
        sum += num % 10;
        num /= 10;
    }

    printf("Sum of the digits is: %d\n", sum);
    return 0;
}

// 14. Check if a given number is a palindrome or not using a while loop:

#include <stdio.h>

int main() {
    int num, originalNum, reversedNum = 0;

    printf("Enter a number: ");
    scanf("%d", &num);

    originalNum = num;

    while(num != 0) {
        reversedNum = reversedNum * 10 + num % 10;
        num /= 10;
    }

    if(originalNum == reversedNum) {
        printf("%d is a palindrome.\n", originalNum);
    } else {
        printf("%d is not a palindrome.\n", originalNum);
    }

    return 0;
}

// 15. Convert a decimal number to binary using a while loop:

#include <stdio.h>

int main() {
    int num, binary[32], i = 0;

    printf("Enter a decimal number: ");
    scanf("%d", &num);

    while(num > 0) {
        binary[i] = num % 2;
        num = num / 2;
        i++;
    }

    printf("Binary representation: ");
    for(int j = i-1; j >= 0; j--) {
        printf("%d", binary[j]);
    }
    printf("\n");

    return 0;
}

// 16. Convert a binary number to decimal using a while loop:

#include <stdio.h>
#include <math.h>

int main() {
    int binary, decimal = 0, base = 1, rem;

    printf("Enter a binary number: ");
    scanf("%d", &binary);

    while(binary > 0) {
        rem = binary % 10;
        decimal = decimal + rem * base;
        binary = binary / 10;
        base = base * 2;
    }

    printf("Decimal representation: %d\n", decimal);

    return 0;
}

// 17. Find the GCD of two numbers using a while loop:

#include <stdio.h>

int main() {
    int a, b;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    while(a != b) {
        if(a > b)
            a = a - b;
        else
            b = b - a;
    }

    printf("GCD is: %d\n", a);

    return 0;
}

// 18. Find the LCM of two numbers using a while loop:

#include <stdio.h>

int main() {
    int a, b, max;

    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);

    max = (a > b) ? a : b;

    while(1) {
        if(max % a == 0 && max % b == 0) {
            printf("LCM is: %d\n", max);
            break;
        }
        max++;
    }

    return 0;
}

// 19. Print all Armstrong numbers between 1 and 1000 using a for loop:

#include <stdio.h>
#include <math.h>

int main() {
    int num, originalNum, remainder, result, n;

    printf("Armstrong numbers between 1 and 1000 are:\n");
    for(num = 1; num <= 1000; num++) {
        originalNum = num;
        result = 0;
        n = log10(num) + 1;

        while(originalNum != 0) {
            remainder = originalNum % 10;
            result += pow(remainder, n);
            originalNum /= 10;
        }

        if(result == num) {
            printf("%d\n", num);
        }
    }

    return 0;
}

// 20. Print all perfect numbers between 1 and 1000 using a for loop:

#include <stdio.h>

int main() {
    int num, i, sum;

    printf("Perfect numbers between 1 and 1000 are:\n");
    for(num = 1; num <= 1000; num++) {
        sum = 0;

        for(i = 1; i <= num / 2; i++) {
            if(num % i == 0) {
                sum += i;
            }
        }

        if(sum == num && num != 0) {
            printf("%d\n", num);
        }
    }

    return 0;
}

All 20 questions and answers related to c loops 👆👇
https://t.me/C_Codes_pro/184

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