write a c program to convert lower case stirng to upper case and upper case string to lower case

#include<stdio.h>
#include<string.h>
main() 
{
   char lower[20] = "aaqib anayat";
    char upper[20] = "AAQIB ANAYAT";
   printf("String before to strupr : %s n", lower);
   strupr(lower);
   printf("String after strupr : %s nn", lower);
    printf("String before to strlwr : %s n", upper);
    strlwr(upper);
   printf("String after strlwr : %s n", upper);

getch(); 
   
}