/* Program# 37
   date : 25-12-2008
   Convert uppercase to Lowercase 
*/

#include <stdio.h>
main(){
char a;
printf("\nEnter a Uppercase alphabet :");
scanf("%c",&a);
if(a>=65 && a<=90){
a=a+32;
printf("\nLowercase letter is %c \n",a);
}
else
printf("\n%c is Not uppercase letter\n",a);
}

$ gcc p37.c  

Now the executable file is stored as a.out, to run
the program,

$ ./a.out

Enter a Uppercase alphabet :H

Lowercase letter is h 
$