C语言isupper()库函数

#include <stdio.h>
#include <ctype.h>

int main () {
   int var1 = 'M';
   int var2 = 'm';
   int var3 = '3';

   if( isupper(var1) ) {
      printf("var1 = |%c| is uppercase character/n", var1 );
   } else {
      printf("var1 = |%c| is not uppercase character/n", var1 );
   }

   if( isupper(var2) ) {
      printf("var2 = |%c| is uppercase character/n", var2 );
   } else {
      printf("var2 = |%c| is not uppercase character/n", var2 );
   }   

   if( isupper(var3) ) {
      printf("var3 = |%c| is uppercase character/n", var3 );
   } else {
      printf("var3 = |%c| is not uppercase character/n", var3 );
   }

   return(0);
}