C <ctype.h> - toupper() Function

The C <ctype.h> toupper() function is used to convert the given character to uppercase according to the character conversion rules defined by the currently installed C locale.

In the default "C" locale, the following lowercase letters abcdefghijklmnopqrstuvwxyz are replaced with respective uppercase letters ABCDEFGHIJKLMNOPQRSTUVWXYZ.

Syntax

int toupper ( int ch );               

Parameters

Return Value

Returns uppercase version of ch or unchanged ch if no uppercase value is listed in the current C locale.

Example:

The example below shows the usage of toupper() function.

#include <stdio.h>
#include <ctype.h>
 
int main (){
  char str[50] = "HELLO World!";

  //converting str into upper case
  int i = 0;
  while(str[i]) {
    str[i] = toupper(str[i]);
    i++;
  }

  //displaying the output
  printf("%s\n", str);   
  return 0;
}

The output of the above code will be:

HELLO WORLD!