Write a c program to change a string from Lower Case to Upper Case

#include<stdio.h>
#include<conio.h>

void upper_string(char*);

void main()
{
    char string[100];
    clrscr();
    printf("Enter a string to convert it into upper case\n");
    gets(string);
    upper_string(string);
    printf("Entered string in upper case is \"%s\"\n", string);
    getch();
}

void upper_string(char *string)
{
    while(*string)
    {
        if ( *string >= 'a' && *string <= 'z' )
        {
            *string = *string - 32;
        }
        string++;
    }
}