SPOJ Small Factorial program in C

Question

Small Factorial

My code is showing 'wrong output' in SPOJ, although it's running without trouble in my compiler.

The code for the program is :

#include<stdio.h>

int factorial(int);

int main(){
    int a[100],t,n,i;
    scanf("%d",&t);
    for(i=0;i<t;i++){
        scanf("%d",&a[i]);
    }
    for(i=0;i<t;i++){
        printf("%d",factorial(a[i]));
        printf("\n");   
    }
    return 0;
}

int factorial(int n){
    if(n==0){
        return 1;
    }
    else if(n==1){
        return 1;
    }
    else{
        return n*factorial(n-1);
    }
}

Answer 1

Your program is getting integer overflow. You need at least 66 bytes to store 100! exactly. An unsigned long long int is usually 8 bytes, and can store up to 1.8 × 10¹⁹. 100! is about 9.3 × 10¹⁵⁷.

You need another way to calculate this value, or use a different language. You could try storing the values in a double or long double, but it isn't going to be exact, so I doubt it will satisfy SPOJ.