integer constant is too large for “long” type [dup

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Closed 8 years ago.

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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

Must be a limitation of dev-c++ support for long long datatype. It compiles fine on MS VC++ 2010.

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.

Answer 3

Try an "ULL" suffix: 600851475143ULL