C/ctype.h/islower

    
//Declaration:  int islower(int ch); 
//Return:       returns nonzero if ch is a lowercase letter; 
                otherwise zero is returned. 

  #include <ctype.h>
  #include <stdio.h>
  int main(void)
  {
    char ch;
    for(;;) {
      ch = getchar();
      if(ch == "."){
         break;
      }
      if(islower(ch)){
         printf("%c is lowercase\n", ch);
      }
    }
    return 0;
  }
         
/*
1
2
b
b is lowercase
f
f is lowercase
r
r is lowercase
e
e is lowercase
d
d is lowercase
A
.
*/