Header File 

ctype.h, wctype.h, mbstring.h 

Category 

Classification Routines 

Prototype 

int isupper(int c); 

int iswupper(wint_t c); 

int _ismbcupper(unsigned int c); 

Description 

Tests for uppercase character. 

isupper is a macro that classifies ASCII-coded integer values by table lookup. The macro is affected by the current locale’s LC_CTYPE category. For the default C locale, c is an uppercase letter (A to Z). 

You can make this macro available as a function by undefining (#undef) it. 

Return Value 

isupper returns nonzero if c is an uppercase letter. 

Example  

#include <stdio.h>
#include <ctype.h>
int main(void)
{
  char c = 'C';
  if (isupper(c))
    printf("%c is an uppercase character\n",c);
  else 
    printf("%c is not an uppercase character\n",c);
  return 0;
}

Portability