//C++ program : To change the letter case (uppercase to lowercase and viceversa)
#include <iostream>
using namespace std;
int main()
{     
    char ch;
    do
      {  cout <<"\n Enter a character (0 to terminate): ";
         ch=getchar();
         if (ch>=65 && ch<=90)        // if uppercase
            ch = ch + 32;             // change to lowercase
         else
             if (ch >=97 && ch <= 122)// if lowercase
             ch = ch -32;             // change to lowercase
         putchar(ch);
      } while (ch!='0');
         
    system ("pause");
    return 0;
}