#include <ctype.h>
    int toupper( int char );

  Returns upper case type of the character

#include <stdio.h> /* including standard library */
//#include <windows.h> /* uncomment this for Windows */
 
#include <ctype.h>
 
int main ( void )
{
  char string[30];
  /* write the Chars "i" and "t" uppercase in the buffer "string" */
  sprintf(string,"%c whant %chis in uppercase",toupper('i'), toupper('t'));
  printf("%s\n",string);
 
return 0;
}

  output:
  user@host:~$ ./toupper 
  I whant This in uppercase