c - Why unsigned int contained negative number

Question

What I know about unsigned numerics (unsigned short, int and longs), that It contains positive numbers only, but the following simple program successfully assigned a negative number to an unsigned int:

  1 /*
  2  * =====================================================================================
  3  *
  4  *       Filename:  prog4.c
  5  *
  6  * =====================================================================================
  7  */
  8 
  9 #include <stdio.h>
 10 
 11 int main(void){
 12 
 13     int v1 =0, v2=0;
 14     unsigned int sum;
 15     
 16     v1 = 10;
 17     v2 = 20;
 18     
 19     sum = v1 - v2;
 20     
 21     printf("The subtraction of %i from %i is %i 
" , v1, v2, sum);
 22     
 23     return 0;
 24 }

The output is : The subtraction of 10 from 20 is -10

Answer 1

%i is the format specifier for a signed integer; you need to use %u to print an unsigned integer.