hex2text

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#define NMAX 101

char *hex2text(const char *const hex) {
  const int n = strlen(hex) - 1;
  assert(n % 2 == 0);
  char *text = malloc(sizeof(char) * (n / 2 + 1));
  if (text == NULL) {
    return NULL;
  }
  text[0] = 0;
  for (int i = 0; i < n; i += 2) {
    char aux[3];
    strncpy(aux, hex + i, 2);
    text[i / 2] = strtol(aux, NULL, 16);
  }
  text[n / 2 + 1] = 0;
  return text;
}

int main() {
  char hex[NMAX], *text;
  if (fgets(hex, NMAX, stdin) != NULL) {
    text = hex2text(hex);
    if (text != NULL) {
      puts(text);
      return 0;
    }
  }
  puts("Error!");
  return 0;
}