#include <stdio.h> // Include standard input-output library
// Function prototype declaration
int sum(int m);
void main() {
int n, s;
// Prompt user to enter a number
printf("Enter a number: ");
// Read user input
scanf("%d", &n);
// Call the recursive sum function
s = sum(n);
// Output the result
printf("Sum of numbers from 1 to %d is %d\n", n, s);
}
// Recursive function to calculate the sum of numbers from 1 to m
int sum(int m) {
if (m == 1) // Base case: when m is 1, return 1
return 1;
else
return m + sum(m - 1); // Recursive case: m + sum of numbers from 1 to m-1
}
Explanation
#include <stdio.h>: This line includes the standard input-output library necessary for functions likeprintfandscanf.Function Prototype:
int sum(int m);declares thesumfunction beforemainso that the compiler knows it exists.mainFunction:int n, s;declares two integer variables:n(for the user’s input) ands(to store the result of the sum).printf("Enter a number: ");prompts the user to enter a number.scanf("%d", &n);reads an integer input from the user and stores it inn.s = sum(n);calls thesumfunction, passing the user-provided numbernand stores the result ins.printf("Sum of numbers from 1 to %d is %d\n", n, s);outputs the result.
sumFunction:- This function calculates the sum of numbers from 1 to
musing recursion. - Base Case: If
mis 1, it returns 1, ending the recursion. - Recursive Case: Otherwise, it adds
mto the result ofsum(m - 1), calling itself withm-1.
- This function calculates the sum of numbers from 1 to
How Recursion Works Here
If n is 4, the function call sequence would be as follows:
sum(4)= 4 +sum(3)sum(3)= 3 +sum(2)sum(2)= 2 +sum(1)sum(1)= 1 (base case)
Adding these up: 4 + 3 + 2 + 1 = 10, so sum(4) returns 10.
Output Example
If the user enters 4, the output will be:
