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cunsigned-integer

C - unsigned int going negative (-ve)

What I know is - UNSIGNED INT cannot take negative values.
If I take the maximum value of an UNSIGNED INT and increment it, I should get ZERO i.e. the minimum value and if I take the minimum value and decrement it, I should get the maximum value.
Then, why is this happening ?

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>

int main()
{
    unsigned int ui;
    ui = UINT_MAX;
    ui ++;
    printf("ui = %d", ui);

    ui = 0;
    ui --;
    printf("\n");
    printf("ui = %d", ui);

    return EXIT_SUCCESS;
}

Output:

ui = 0
ui = -1
Solution

  • You pass the value to an ellipsis function (printf). You should expect nothing about the signedness here.

    The %d in the format string controls the sign of the displayed value. There is a cast inside the printf function since you selected the %d. That's why you see a signed value that is equivalent to the binary value FFFFFFFF1.

    1 Assuming a 32 bit width for integer.