Question

Here is one program

#include<stdio.h>
#include<stdlib.h>
int main()
{
 unsigned char a=0x80;
 printf("%d\n",a<<1);
}

The output of above is 256
Now here is one more version of above program

#include<stdio.h>
#include<stdlib.h>
int main()
{
 unsigned char a=0x80;
  a=a<<1;
 printf("%d\n",a);
}

The output of above is

0

As far as my understanding is I am not able to see any difference between the two?
i.e. why is output coming 256 in first one and 0 in second program what is the difference in statements in both?

Answer 1

The expression a << 1 is of type int according to the C language’s type-promotion rules. In the first program, you are taking this int, which now has the value 0x100, and passing it directly to printf(), which works as expected.

In the second program, your int is assigned to an unsigned char, which results in truncation of 0x100 to 0x00.