How can I make to signed char in C function like unsigned - c

Question

I'm trying to encode_char_in C that replace the bit of even index between the odd bit index, like this
'W' = 57h = 0101_0111
ABh = 1010_1011
and because char in C may become to negative number, I can't switch between the bits (only in signed char — it works).
It gave me another value
in this code below.
#include <stdio.h>
#include <limits.h>
#define TRUE 1
#define ONE 1
char codeBinPair(char str);
void main()
{
char str[2] = { 182,NULL };
unsigned char ch = 'W';
printf("ch = %x\n", ch);
ch = codeBinPair(ch);
printf("ch = %x\n", ch);
ch = codeBinPair(ch);
printf("ch = %x\n", ch);
}
char codeBinPair(char str)
{
int idx = 0;
char ch1 = str, ch2 = 0, mask = ONE;
while (TRUE)
{
mask <<= ONE;
mask &= ch1;
mask >>= ONE;
ch2 |= mask;
// Initialize the mask
mask = ONE;
mask <<= idx;
mask &= ch1;
mask <<= ONE;
ch2 |= mask;
// Index next loop we want to replace
idx += 2;
// If We Finish whole Byte
if (idx == CHAR_BIT)
return ch2;
// Initialize the mask
mask = ONE;
mask <<= idx;
}
}

Answer 1

Change all the char in codeBinPair to unsigned char.
unsigned char codeBinPair(unsigned char str)
{
int idx = 0;
unsigned char ch1 = str, ch2 = 0, mask = ONE;
while (TRUE)
{
mask <<= ONE;
mask &= ch1;
mask >>= ONE;
ch2 |= mask;
// Initialize the mask
mask = ONE;
mask <<= idx;
mask &= ch1;
mask <<= ONE;
ch2 |= mask;
// Index next loop we want to replace
idx += 2;
// If we finish whole byte
if (idx == CHAR_BIT)
return ch2;
// Initialize the mask
mask = ONE;
mask <<= idx;
}
}

Answer 2

char codeBinPair(char str)
{
int idx = CHAR_BIT - 1;
char mask = 1;
char maskA = 0;
char maskB = 0;
// str = 'W'
while (idx--) // Loop 7 times = 7 bits in char
{
//To Replace the odd bits
maskA |= mask & str;
mask <<= 1;
//To Replace the even bits
maskB |= mask & str;
mask <<= 1;
}
// to shift ths bits of 2 masks
maskA <<= 1;
maskB >>= 1;
// Subtraction between the 2 masks will give the encoded
return maskA - maskB;}
}