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Factorial Using Recursion (C)

📌 Problem

Find the factorial of a number using recursion.

    if (n == 0 || n == 1)
        return 1;

    return n * factorial(n--);
}

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Wrong Code: 

return n * factorial(n--);
Right Code: 
return n * factorial(n-1);
Factorial of n:

n! = n × (n-1) × (n-2) × ... × 1

    if (n == 0 || n == 1)
        return 1;

    return n * factorial(n-1);
}
5! = 5 × 4 × 3 × 2 × 1 = 120

#include <stdio.h>

int factorial(int n) {
    if (n == 0 || n == 1)
        return 1;
    return n * factorial(n-1);
}// post decrease // stack overflow 


int main() {
    int num = 5;
    printf("Factorial of %d is %d\n", num, factorial(num));
    return 0;
}

Let’s understand how recursion works for n = 5:

factorial(5)
= 5 * factorial(4)
= 5 * 4 * factorial(3)
= 5 * 4 * 3 * factorial(2)
= 5 * 4 * 3 * 2 * factorial(1)
= 5 * 4 * 3 * 2 * 1
= 120

Base Case 

if (n == 0 || n == 1)
    return 1;
stop recorsion

return n * factorial(n - 1);
Reduces the problem size Calls function again with smaller value

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