Concept behind these four lines of tricky C code

Question

Why does this code give the output C++Sucks? What is the concept behind it?

#include 

double m[] = {7709179928849219.0, 771};

i         


        

Answer 1

More readable version:

double m[2] = {7709179928849219.0, 771};
// m[0] = 7709179928849219.0;
// m[1] = 771;    

int main()
{
    if (m[1]-- != 0)
    {
        m[0] *= 2;
        main();
    }
    else
    {
        printf((char*) m);
    }
}

It recursively calls main() 771 times.

In the beginning, m[0] = 7709179928849219.0, which stands for C++Suc;C. In every call, m[0] gets doubled, to "repair" last two letters. In the last call, m[0] contains ASCII char representation of C++Sucks and m[1] contains only zeros, so it has a null terminator for C++Sucks string. All under assumption that m[0] is stored on 8 bytes, so each char takes 1 byte.

Without recursion and illegal main() calling it will look like this:

double m[] = {7709179928849219.0, 0};
for (int i = 0; i < 771; i++)
{
    m[0] *= 2;
}
printf((char*) m);