integer constant is too large for "long" type [duplicate]

Question

Possible Duplicate:
long long in C/C++

Writing a simple program for a project Euler problem. Refuses to compile because "integer constant is too large for "long" type", even though it should be well within the size limits of an unsigned long long. Using the dev-c++ compiler.

code in question:

#include <iostream>

bool isprime (unsigned long long i)
{
    if(i==1||i==0) return false;
    if(i==2) return true;
    for(unsigned long long k=2;k!=i-1;k++)
    {      
        if(i%k==0) return false;
    }
    return true;
}

int main()
{
    for(unsigned long long i=600851475143;i>=0;i--) //problematic line
    {
        if(isprime(i))
        {
            std::cout<<i;
            std::cin.get();
            return 0;
        }
    }
}

Answer 1

Try an "ULL" suffix: 600851475143ULL

Answer 2

Your literal as typed has type int which isn't big enough to hold the value. Try 600851475143ULL as a first fix.

Note even with that, your for loop will never terminate since an unsigned can never be less than 0. Instead, use a long long and 600851475143LL.