Go4Expert - Validating data

Hey all

Basically, I am trying to get my head around data validation. I am very new to C, in fact I have only been doing it a few days.

I am trying to make a simple currency converter that validates that the data is numerical. Alos, I would like the app to exit if the user enters exit (in upper or lower case)

This is what I have so far

Code:

#include <stdio.h>

#include <conio.h>



int main()

{

        float input; //for input

        float rate =1.89712; //for rate

        float result; //for output



   printf("Please enter the amount you want to convert in GBP. "); //Get users input

   scanf ("%f",&input);



   clrscr();

        result = input * rate; //do some maths

   printf("£%.2f is equal to %.2f euros\n",input, result);//show output



}

it does what I want but as I said, I need it to check the user has entered correct data and if not, loop back so they can input again. Also, I need it to exit when the user enters enter.

edit: oh yea, btw, I only want it to convert from one to another at the mo

Thankyou!