Header File 

ctype.h, mbstring.h 

Category 

Conversion Routines 

Prototype 

int toupper(int ch); 

int towupper(wint_t ch); // Unicode version 

unsigned int _mbctoupper(unsigned int c); 

Description 

Translates characters to uppercase. 

toupper is a function that converts an integer ch (in the range EOF to 255) to its uppercase value (A to Z; if it was lowercase, a to z). All others are left unchanged. 

towupper is the Unicode version of toupper. It is available when Unicode is defined. 

Return Value 

toupper returns the converted value of ch if it is lowercase; it returns all others unchanged. 

Example  

#include <string.h>
#include <stdio.h>
#include <ctype.h>
int main(void)
{
   int length, i;
   char *string = "this is a string";
   length = strlen(string);
   for (i=0; i<length; i++)
   {
      string[i] = toupper(string[i]);
   }
   printf("%s\n",string);
   return 0;
}

Portability