Problems to calculate the largest prime int in C

Question

Hello.

I’m trying to calculate the largest prime number that fits into an int variable. My idea was to start with the largest int, and go checking in descending order until you find the first prime number. When I try to run the program I get the message: "maiorprimo.exe has stopped working. Windows is checking a solution to the problem."

Follows the code:

#include <stdio.h>
#include <limits.h>

int main(){
    int primo=0;
    int num=INT_MAX;
    for(num; num>0; num--){
        primo=ePrimo(num);
        if(primo==1){
            printf("%d eh primo" ,num);
            break;
        }
    }
}

int ePrimo(int n){
    int i;
    int cont;
    for(i=0; i<=n; i++){
        if(n%i==0){
            cont++;
        }
    }
    if(cont==2)
        return 1;
    else
        return 0;
}

Answer 1

In function main() flames the function ePrimo() with the value INT_MAX.

In function ePrimo() your cycle

for (i = 0; i <= n; i++) { /* ... */ }

is an infinite cycle.

i is at all times less than or equal to INT_MAX.

Tip: start checking in 2 (instead of 0) and goes to the square root of n. If you catch a divider, just return it 0 without calculating other dividers.