Question

1) If c is type char and i type int, what is assigned to c and i?
    Give answers in hex. Assume c is one byte, and i is four 
    bytes. Explain.

    c = 240;
    i = c;

2) If c is type unsigned char and i type int, what is assigned to 
    c and i? Give answers in hex. Explain

    c = 240;
    i = c;

3) If c is type signed char and i type int, what is assigned to 
    c and i? Give answers in hex. Explain

    c = 240;
    i = c;
     

Answer 1

explanation:-

as we know

Type	Storage size	Value range
char	1 byte	-128 to 127 or 0 to 255
unsigned char	1 byte	0 to 255
signed char	1 byte	-128 to 127

The first bit is the sign-bit, leaving us with 11110000. Per two's complement, if we complement it (getting 00001111), and then add one, we get 00010000 -- this is 16. As our starting point, 240 = F0 in hex, and 11110000 in binary.

When it converts the signed char to signed int, it doesn't say "this would be 240 if it's unsigned", it says "this is -16, make it an int of -16", for which the 32-bit two's complement representation is FFFFFFF0, because it must be the negative value for the full size of int (this is called sign-extension):

+36 as a 32-bit value: 000000000000000000000000 11110000
complement:            111111111111111111111111 00001111
add one:               111111111111111111111111 00010000

Or, in hex, FFFFFFF0.

This is why you must be careful with printf("%x", c); (and relatives) -- if you intend to just get a two-digit value, and chars are signed, you may wind up with eight digits instead. Always specify "unsigned char" if you need it to be unsigned

#include <stdio.h>
int main()
{
   char c=240;
   int i=c;
  
   printf("c : HEX: = %X",c);
   printf("\ni : HEX: = %X",i);
  
   return 0;
}

output:

c :HEX: =fffffff0

c :HEX: =fffffff0

#include <stdio.h>
int main()
{
unsigned char c=240;
   int i=c;
  
   printf("c : HEX: = %X",c);
   printf("\ni : HEX: = %X",i);
  
   return 0;
}

output:

c :HEX: =f0

c :HEX: =f0

#include <stdio.h>
int main()
{
signed char c=240;
   int i=c;
  
   printf("c : HEX: = %X",c);
   printf("\ni : HEX: = %X",i);
  
   return 0;
}

output:

c :HEX: =fffffff0

c :HEX: =fffffff0