gistfile1.txt

#include<stdio.h>
#include<stdlib.h>
#define MAX 4096

int h2d(char *p){
        int result = 0;
        for(int i = 1; i > -1; i--){
                if(*p >= '0' && *p <= '9')
                        result += (*p - '0')*(i?16:1);
                else if(*p >= 'a' && *p <= 'f')
                        result += (*p - 'a'+10)*(i?16:1);
                else if(*p >= 'A' && *p <= 'F')
                        result += (*p - 'A'+10)*(i?16:1);
                p += 1;
        }
        return result;
}
int main(){
        char *line = (char*)calloc(MAX, 1);
        fgets(line, MAX, stdin);
        for(int i = 0; line[i] != '\0'; i++){
                if(line[i] == '0'){
                        i++;
                        if(line[i] == 'x'){
                                i++;
                                fprintf(stderr, "%d ", h2d(line+i));
                                i++;
                        }
                }
        }
        return 0;
}