types - long long in C/C++

Question

I am trying this code on GNU's C++ compiler and am unable to understand its behaviour:

#include <stdio.h>;

int main()
{
    int  num1 = 1000000000;
    long num2 = 1000000000;
    long long num3;
    //num3 = 100000000000;
    long long num4 = ~0;

    printf("%u %u %u", sizeof(num1), sizeof(num2), sizeof(num3));
    printf("%d %ld %lld %llu", num1, num2, num3, num4);
    return 0;
}

When I uncomment the commented line, the code doesn't compile and is giving an error:

error: integer constant is too large for long type

But, if the code is compiled as it is and is executed, it produces values much larger than 10000000000.

Why?

Answer 1

The letters 100000000000 make up a literal integer constant, but the value is too large for the type int. You need to use a suffix to change the type of the literal, i.e.

long long num3 = 100000000000LL;

The suffix LL makes the literal into type long long. C is not "smart" enough to conclude this from the type on the left, the type is a property of the literal itself, not the context in which it is being used.