C++ change char to lowercase code example

Example 1: convert characters to lowercase c++

str[i] = tolower(str[i]);

Example 2: c++ convert lowercase to uppercase

/* toupper example */
#include <stdio.h>
#include <ctype.h>
int main ()
{
  int i=0;
  char str[]="Test String.\n";
  char c;
  while (str[i])
  {
    c=str[i];
    putchar (toupper(c));
    i++;
  }
  return 0;
}