isupper() - ctype.h

The C library function int isupper(int c) checks whether the passed character is uppercase letter.
This function returns a non-zero value(true) if c is an uppercase alphabetic letter else, zero (false).

Syntax

int isupper(int c);

Example

#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);
}

Output / Return Value

var1 = |M| is uppercase character
var2 = |m| is not uppercase character
var3 = |3| is not uppercase character

Limitations

Alternatives / See Also

Reference