Toggle case of letters of a string.

//Program to toggle case of letters of a string.
#include<iostream.h>
#include<conio.h>
#include<stdio.h>
#include<ctype.h>
void main()
{
    clrscr();
    char a[80];
    cout<<"Enter a string: ";
    gets(a);
    for(int i=0;a[i]!='\0';i++)
    {
        if(isupper(a[i]))
        a[i]=tolower(a[i]);
        else
        a[i]=toupper(a[i]);
    }
    puts(a);
    getch();
}