C program to change the case of a string

•  When 1 string is in lower case & another is in upper case

#include<stdio.h>
#include<conio.h>
#include<string.h>
main()
{
char st[20],st1[20];
int l;
clrscr();
printf("enter 1st string: ");
gets(st);
printf("\n enter 2nd string:");
gets(st1);
printf("\n string 1 in lower case is:");
strlwr(st);
puts(st);
printf("\n string 2 in upper case is:");
strupr(st1);
puts(st1);
getch();
}