Thread: Input check problem with numbers

I study your example and I have to say that is NOT good to combine the cin.ignore() method with the method of conversion. There is a problem in input stream and it's difficult to discover it. Anyway here is my source:

Do you think that I can avoid the cin.clear and cin.ignore parts ?

Code:

// 
// File:   temp.cc
// Author: blackslash13
//
// Created on 29 Νοέμβριος 2007, 11:06 μμ
//

#include <stdlib.h>
#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
#include <limits>

bool inputDouble(std::string prompt, double &val)
{
	std::string input;
	for(;;) 
	{
		std::stringstream sstr;
		std::cout << prompt;
		if (!std::getline(std::cin, input))   
			return false;  // Failed to read input. 
		sstr << input;
		if (sstr >> val) {
			return true;
		}
		else
		{
			std::cout << "Error, not a valid number" << std::endl;
		}
	}
}

double fahrenheitToCelsius(double fahrenheit)
{
    double celsius;
    
    celsius = (fahrenheit-32)/1.8;
    return  celsius;
}

double celsiusToFahrenheit(double celsius)
{
	double fahrenheit;
	
	fahrenheit = 1.8 * celsius + 32 ;
	return fahrenheit;
}

void  makeTable(double start, double end, double step, double choice)
{
	using namespace std;
	cout.setf(ios::fixed);
	double i(0),fahr,celsius;
        
        if(choice==1)
        {
            	for(i=start; i<=end; i+=step)
                {	
		fahr=celsiusToFahrenheit(i);
		cout << setprecision(2) << setw(5) << i << "\t\t" <<  fahr << endl;
                }
        }
        else
        {
            for(i=start; i<=end; i+=step)
                {	
		celsius=fahrenheitToCelsius(i);
		cout << setprecision(2) << setw(5) << i << "\t\t" <<  celsius << endl;
                }
            
        }

}
	

//
// 
//
int main(int argc, char** argv) {
    
    {
	using namespace std;
	
	double choice,choice2;
	double degree,lowBound,maxBound,step;
	
	cout << "Select a number" << endl
	     << "1. Celsius to Fahrenheit\n2. Fahrenheit to Celsius" << endl
	     << "Your Choice:";
	
	cin >> choice;
	
	while(!cin.good() || choice<1 || choice>2)
	{
		cin.clear();
		cin.ignore(numeric_limits<streamsize>::max(),'\n');
		cout << "Not valid selection.... Your Choice:";
		cin >> choice;
	}
	
	if(choice == 1)
	{
		cout << "Select a number" << endl
	     	<< "1. Specific conversion\n2. Print table list" << endl
	     	<< "Your Choice:";
		cin >> choice2;
                
                
	
		while(!cin.good() || choice2<1 || choice2>2)
		{
			cin.clear();
			cin.ignore(numeric_limits<streamsize>::max(),'\n');
			cout << "Not valid selection.... Your Choice:";
			cin >> choice2;
		}
                
                /* Thrash the garbage from input strem */
                cin.clear();
		cin.ignore(1,'\n');
                
		if(choice2==1)
		{
                        
                  	while(!inputDouble("Enter Celsius temperature degree:", degree) || degree<=-316 || degree>=316)
			{
				cout << "Not valid selection....";
			}
			
			cout << degree << " Celsius = " << celsiusToFahrenheit(degree) << " Fahrenheit." << endl;
		}
		else
		{
			while(!inputDouble("Enter Celsius lower bound degree:",lowBound) || lowBound<=-316 || lowBound>=316)
			{
				cout << "Not valid selection....";
			}

			while(!inputDouble("Enter Celsius maximum bound degree:",maxBound) || maxBound<=-316 || maxBound>=316)
			{
				cout << "Not valid selection....";
			}

			while(!inputDouble("Enter increment value for the list:",step) ||  step<=0)
			{
				cout << "Not valid selection....";
			}
			
			cout << "Celsius\t\tFahrenheit" << endl;
			makeTable(lowBound, maxBound, step,1);
		}
        }
        else
	{
           	cout << "Select a number" << endl
	     	<< "1. Specific conversion\n2. Print table list" << endl
	     	<< "Your Choice:";
		cin >> choice2;
                
                
	
		while(!cin.good() || choice2<1 || choice2>2)
		{
			cin.clear();
			cin.ignore(numeric_limits<streamsize>::max(),'\n');
			cout << "Not valid selection.... Your Choice:";
			cin >> choice2;
		}
                
                /* Thrash the garbage from input strem */
                cin.clear();
		cin.ignore(1,'\n');
            

            if(choice2==1)
		{
                        
                  	while(!inputDouble("Enter Fahrenheit temperature degree:", degree) || degree<=-316 || degree>=316)
			{
				cout << "Not valid selection....";
			}
			
			cout << degree << " Fahrenheit = " << fahrenheitToCelsius(degree) << " Celsius." << endl;
		}
		else
		{
			while(!inputDouble("Enter Fahrenheit lower bound degree:",lowBound) || lowBound<=-316 || lowBound>=316)
			{
				cout << "Not valid selection....";
			}

			while(!inputDouble("Enter Fahrenheit maximum bound degree:",maxBound) || maxBound<=-316 || maxBound>=316)
			{
				cout << "Not valid selection....";
			}

			while(!inputDouble("Enter increment value for the list:",step) || step<=0)
			{
				cout << "Not valid selection....";
			}
			
			cout << "Fahrenheit\tCelsius" << endl;
			makeTable(lowBound, maxBound, step,2);
		}
            
	}
	return 0;
}
	
    
    return (EXIT_SUCCESS);
}

Thanks matsp, you rock dude!!!!