C Program to Find Factorial of a Number - Loop & Recursion
Find Factorial Using a Loop
#include <stdio.h>
int main() {
int n;
long long factorial = 1; // factorial can grow quickly, so use a large type
printf("Enter a non-negative integer: ");
scanf("%d", &n);
// Check for negative input
if (n < 0) {
printf("Factorial is not defined for negative numbers.\n");
return 0;
}
// Multiply numbers from 1 to n
for (int i = 1; i <= n; ++i) {
factorial *= i;
}
printf("Factorial of %d = %lld\n", n, factorial);
return 0;
}Enter a non-negative integer: 5
Factorial of 5 = 120
The factorial of a number n (written n!) is the product of all integers from 1 to n. An iterative solution multiplies numbers in sequence, storing the result in a variable.
Find Factorial Using Recursion
#include <stdio.h>
// Recursive function declaration
long long factorial(int n) {
// Base case: 0! is defined as 1
if (n == 0)
return 1;
else
// Recursive case: n! = n * (n-1)!
return n * factorial(n - 1);
}
int main() {
int n;
printf("Enter a non-negative integer: ");
scanf("%d", &n);
if (n < 0) {
printf("Factorial is not defined for negative numbers.\n");
} else {
printf("Factorial of %d = %lld\n", n, factorial(n));
}
return 0;
}Enter a non-negative integer: 5
Factorial of 5 = 120
Recursion solves a problem by defining a function that calls itself with a smaller argument. Each call reduces the problem size until a base case is reached. In this factorial example, the base case is 0, and the recursion continues until n equals 0. Remember to ensure the base case is reachable; otherwise, the program will run indefinitely.
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