#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>   // for toupper()
#include <string.h>   // for strcpy()

typedef char* str;

// How could/would you fix this method?
str upperify(str s) {
  char result[strlen(s)+1];       // allocate space on stack

  strcpy(result, s);                   // copy string argument into result
  for (char *p=result; *p != '\0'; p++) {
    *p = toupper(*p);               // upperfy, char by char
  }
  printf("%s\n", result);
  return result;  // this is an error -- returning a pointer to stack memory that
                         // is about to be freed
}

//------------------------------------------------------
// mainline
//------------------------------------------------------
int main(int argc, char *argv[]) {
  int argIndex;

  // args before upperify'ing
  printf("1st phase (print args):\n");
  for (argIndex=0; argIndex<argc; argIndex++) {
    printf("%3d: %s\n", argIndex, argv[argIndex]);
  }

  printf("\n2nd phase (upperfy them):\n");
  // upperify them
  for (argIndex=0; argIndex<argc; argIndex++) {
    argv[argIndex] = upperify(argv[argIndex]);
  }

  // print them
  printf("\n3rd phase (print them):\n");
  for (argIndex=0; argIndex<argc; argIndex++) {
    printf("%3d: %s\n", argIndex, argv[argIndex]);
  }

  return EXIT_SUCCESS;
}