Write a program in C to calculate the sum of numbers from 1 to n using recursion. Input: Input a positve integer n. Output : Compute the summation of 1+2+...+n. Sample of Input: 5 Sample of Output: 15

Sure, I can help you with that. Here's the C program to calculate the sum of numbers from 1 to n using recursion:

#include <stdio.h>

int sum(int n);

int main() {
    int n, result;
    printf("Enter a positive integer: ");
    scanf("%d", &n);
    result = sum(n);
    printf("The sum of numbers from 1 to %d is %d.\n", n, result);
    return 0;
}

int sum(int n) {
    if (n == 0) {
        return 0;
    } else {
        return n + sum(n-1);
    }
}

Explanation:

The program takes a positive integer `n` as input from the user and calls the `sum()` function with `n` as argument.

The `sum()` function is a recursive function that takes an integer `n` as input and returns the sum of numbers from 1 to `n`.

If `n` is 0, the function returns 0. Otherwise, it adds `n` to the sum of numbers from 1 to `n-1` by calling itself recursively with `n-1` as argument.

Finally, the program outputs the result, which is the sum of numbers from 1 to `n`.