Question

Can you guys please explain the below program

int main() 
{   
 int max = ~0; 
 printf("%d\n",max);    
 return 0; 
}

AFAIK ~ will flip the bits. In this case i.e ~0 will set all the bits into 1. So max variable should contain MAX value but I am getting o/p as -1. So can anyone here please tell me why I am getting o/p as -1.

Answer 1

Why did you expect to obtain the “max value”? In 2’s-complement signed representation all-1 bit pattern stands for -1. It is just the way it is.

Maximum value in 2’s-complement signed representation is represented by 01111...1 bit pattern (i.e the first bit is 0). What you got is 1111...1, which is obviously negative since the very first bit – sign bit – is 1.

If you want an example where complemented zero produces a “max value”, use unsigned representation

int main() {   
  unsigned max = ~0u; 
  printf("%u\n", max);    
}