[RESOLVED] C++ program runs but i get garbage as an output

[caesar2004]

Im using visual c++ 6.0

#include <iostream.h>
#include <conio.h>
#include <string.h>

class customer
{
private:
	char cardname[20];
	float creditlimit;
	float amountspent;
	float amountleft;
	calculate();
	
	
	
public:
	void input();
	void output();
	
};

void customer::input()
{
	cout<<"Please enter the card name: ";
	cin>>cardname;
	cout<<"Please enter the credit limit: ";
	cin>>creditlimit;
	cout<<"Please enter the amount spent: ";
	cin>>amountspent;
}

customer::calculate()
{
	
	amountleft = creditlimit - amountspent;
	
}

void customer::output()
{

	cout<<"Thank you "<<cardname<<" you have "<<amountleft<<" left.";
}

void main()
{
	customer c1;
	c1.input();
	c1.output();
	getch();
}

for example if i put the credit limit at 500 and the amount spent at 200 i get asdfasdf123123!@+800 for an answer

any ideas?