cin.fail

This is a discussion on cin.fail within the C++ Programming forums, part of the General Programming Boards category; can someone tell me why this cin.fail statement will not work. thanks Code: #include <iostream> using namespace std; double balance; ...

  1. #1
    Registered User
    Join Date
    Mar 2004
    Posts
    14

    cin.fail

    can someone tell me why this cin.fail statement will not work.
    thanks
    Code:
    #include <iostream>
    using namespace std;
    
    double balance;							
    double charge(double charge_amount);
    double payment(double pay_amount);
    void quit();
    void display();
    
    int main()
    {
    	char trans;								 	
    	double chargeAmt;								
    	double payAmt;									
    
    	cout<<"Enter beginning balance. ";						
    	cin>>balance;											
    	cout<<endl;									
    
    	do
    	{
    		cout<<"Enter transaction.(C,P,D,Q) ";					
    		cin>>trans;								
    		cout<<endl;		
    
    		if (trans == 'C' || trans == 'c')
    		{
    			cout<<"Enter amount of charge. ";				
    			cin>>chargeAmt;							
    				
    				if (cin.fail())						
    				{	
    				cout<<"ERROR: Bad input!";			        
    					return 1;
    				}
    
    			charge(chargeAmt);
    			cout<<"Your new balance is "<<balance;				
    			cout<<endl;							
    		}
    	
    		
    		else if (trans == 'P'|| trans == 'p')
    		{
    			cout<<"Enter payment. ";					
    			cin>>payAmt;							
    		
    
    			payment(payAmt);
    			cout<<"Your new balance is "<<balance;				
    			cout<<endl;							
    		}
    
    		else if (trans == 'D' || trans == 'd')
    		{
    			display();							
    		}
    
    		else if (trans == 'Q' || trans == 'q')
    		{
    			quit();								
    		}
    
    		else
    			cout<<"Not Valid";
    			cout<<endl;
    	}
    	while (trans != 'Q');
    	
    
    return 0;
    }
    
    double charge (double charge_amount)
    	{
    		balance = balance + charge_amount;
    		return balance;
    	}
    
    double payment(double pay_amount)
    	{
    		balance = balance - pay_amount;
    		return balance;
    	}
    
    void display()
    	{
    		cout<<"Your balance is "<<balance;	
    		cout<<endl;
    	}
    
    
    void quit()
    	{
    		cout<<"Good Bye!";
    		cout<<endl;
    	}
    Last edited by bj31t; 04-01-2004 at 01:32 PM.

  2. #2
    unleashed alphaoide's Avatar
    Join Date
    Sep 2003
    Posts
    696
    It works as I expected. It 's just probably not what you expected.
    Input: 100 -> no error msg
    Input: kkk -> error msg
    Input: 100k -> no error msg, because it only reads the '100' and 'k' is left in the stream for another input method to fetch. I suppose you want this kind of input to give error message, so what you need to is, not sure, but read the input as a string and make sure all characters in the string are digits.
    source: compsci textbooks, cboard.cprogramming.com, world wide web, common sense

  3. #3
    Registered User
    Join Date
    Mar 2004
    Posts
    14
    i am wanting it to only take in numbers as input and give an error message for anything else.

  4. #4
    Magically delicious LuckY's Avatar
    Join Date
    Oct 2001
    Posts
    856
    Try getline() then check the input instead.

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