tolower

    #include <cctype>
    int tolower( int char );

  Returns lower case type of the character

#include <iostream> /* including standard library */
#include <cctype>
 
using namespace std;
int main ( void )
{
  /* convert the Chars "I" and "T" to lowercase */
  cout << static_cast<char>(tolower('I')) << " WHANT " << static_cast<char>(tolower('T')) << "HIS IN LOWERCASE" << endl;
 
return 0;
}

  output:
  i WHANT tHIS IN LOWERCASE