✅ Day 4 solution - DSA with C

 Find the GCD of Two Numbers Using Recursion

GCD (Greatest Common Divisor) using Euclidean Algorithm:

#include <stdio.h>

int gcd(int a, int b) {
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

int main() {
    int num1, num2;
    printf("Enter two numbers: ");
    scanf("%d %d", &num1, &num2);
    printf("GCD of %d and %d is %d\n", num1, num2, gcd(num1, num2));
    return 0;
}

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✅ 2. Recursive Function to Calculate Power (xⁿ)

#include <stdio.h>

int power(int x, int n) {
    if (n == 0)
        return 1;
    return x * power(x, n - 1);
}

int main() {
    int base, exponent;
    printf("Enter base and exponent: ");
    scanf("%d %d", &base, &exponent);
    printf("%d^%d = %d\n", base, exponent, power(base, exponent));
    return 0;
}

---

✅ 3. Reverse an Array Using Recursion

#include <stdio.h>

void reverse(int arr[], int start, int end) {
    if (start >= end)
        return;
    
    // Swap
    int temp = arr[start];
    arr[start] = arr[end];
    arr[end] = temp;

    reverse(arr, start + 1, end - 1);
}

int main() {
    int arr[100], n;
    printf("Enter number of elements: ");
    scanf("%d", &n);

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

    reverse(arr, 0, n - 1);

    printf("Reversed array:\n");
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);

    return 0;
}