Is it safe to subtract unsigned integers?

Question

The following C code displays the result correctly -1.

#include <stdio.h>

main()
{

    unsigned x = 1;
    unsigned y=x-2;

   printf("%d", y );

}

• But in general, is it always safe to do a subtraction involving unsigned integers?

• The reason I ask this question is because I want to make some conditions as follows:

  unsigned x = 1; // x was defined by someone else as unsigned, 
  // which I had better not to change.
  for (int i=-5; i<5; i++){
    if (x+i<0) continue
    f(x+i); // f is a function
  }
  

  Is it safe to do this?

• How do unsigned integers and signed integers differ in representing integers? Thank!

Answer 1

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Answer 2

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  unsigned y=x-2;
  

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Answer 3

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int y = (int)x;

// Do your stuff with *y*

x = (unsigned)y;

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long y = (long)x;

// Do your stuff with *y*

x = (unsigned)y;

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long y = (long)x;

// Do your stuff with *y*

assert( y >= 0L );
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Answer 4

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#include <stdio.h>

main()
{

    unsigned x = 1;
    unsigned y=x-2;

   printf("%u", y );
}

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Answer 5

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Answer 6

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Answer 7

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