Programming in C to convert a letter from upper to lower case and vice versa

#include<stdio.h>
#include<conio.h>
#include<ctype.h>
void main()
{
char c;
clrscr();
printf("\n * Enter 'E' to exit");
printf("\n * Enter only one character at a time");
while (c!='1')
{
printf("\nEnter a character;");
c=getche();
if (c==toupper(c))
printf("\t   It's Lower case : %c",c+32);
else
printf("\t   It's Upper case : %c",c-32);
}
getch();
}