How to concatenate two integers in C

by 
unsigned concatenate(unsigned x, unsigned y) {
    unsigned pow = 10;
    while(y >= pow)
        pow *= 10;
    return x * pow + y;        
}

Proof of compilation/correctness/speed

I avoid the log10 and pow functions, because I’m pretty sure they use floating point and are slowish, so this might be faster on your machine. Maybe. Profile.

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