# So, I used INT , The following way is working for some other API but not this API :(

That should work.

Given this dll:

#include <stdio.h>

__declspec(dllexport) unsigned char __stdcall getChar() {
    unsigned char c = (unsigned char)( rand() & 0xFF );
    printf( "Returning %d\n", c );
    return c;
}
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This script:

#! perl -slw
use strict;
use Win32::API;

my $getChar = Win32::API->Import( 'junkdll', 'int getChar()' )
    or die $!, $^E;

print getChar() for 1 .. 10;
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Produces this output:

C:\test>t-w32api.pl
Returning 41
41
Returning 35
35
Returning 190
190
Returning 132
132
Returning 225
225
Returning 108
108
Returning 214
214
Returning 174
174
Returning 82
82
Returning 144
144
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Not the most convenient form (numeric) to receive 'char' data, but you seem to want the numeric value anyway. You're just working too hard at trying to convert the value when there is no need to.