#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>
#include <assert.h>  //** need assert for malloc check

// convert "hello world" to "HELLO WORLD"
int main(int argc, char ** argv){
  char * s = "hello world";
  int len = strlen(s);   //** calculate strlen only once
  char * t = malloc(len+1);  //**  alloc string buffer
  assert(t);  //** check for malloc error
  int i = 0;
  for ( ; i < len; ){   //**  move strlen out of loop
    t[i] = toupper(s[i]);
    i++;   //**
  }
  t[len] = '\0';
  printf("t: %s \n", t);
  free(t); //**
}