Prime number tester

prime(sieve).c

typedef int bool;
#define true 1
#define false 0
bool prime(long long int n){
    long long int i;
    if(n<=0 || n==1 || (n%2==0 && n!=2)){
        return false;
    }
    else if(n==2 || n==3){
        return true;
    }
    for(i=3;i<(int)sqrt(n)+1;i=i+2){
        if(n%i==0) return false;
    }
    return true;
}