A very simple program in C that quickly gets all signed chars from 0 till 255 and their unsigned counter parts and hex code.

Unsignedchar_signedchar.c

#include <stdio.h>

typedef
   union
      mc {
          char rc;
          unsigned char uc;
      } mychar;
      
mychar ch;      

int main() {
    ch.uc=0;
    for (int i=0;i<256;i++){
        printf("unsigned %3d; signed %4d; hex %0X\n",ch.uc,ch.rc,ch.uc);
        ch.uc++;
    }
	return 0;
}