Accepting integer and character input

[farmerdwight]

Hello, I'm wanting to write a program that reads in two integers at a time and prints them out. Simple enough but I also want to make it so that if you input a certain character like the symbol "|", then the while-loop will quit. However, I don't see how I can accept both integers and characters. I use two integers value1 and value2 to hold my integers but they can't accept characters. Is my only option to use just char and then get the character representation of a number? However, if my number is large enough, wouldn't it exceed the capacity of char?

This is what I have so far. Thanks!

#include "std_lib_facilities.h"

int main() {

	int value1, value2;

	while (1) {
		cout << "Input value1: ";
		cin >> value1;
		cout << "Input value2: ";
		cin >> value2;
		cout << "Value1 is: " << value1 << " and Value2 is: " << value2 << "\n";
	}
	
	cin.get();
	return 0;
}

[newbiee999]

You can use strings.

int main()
{

string value1, value2;     // list of chars is a string (which includes numbers and symbols)

while(true){
         cout << "Input value1: ";
         cin >> value1;
         if (value1 == "|")   // if user enters "|", break will terminate the while loop
         { break; }
         cout << "Input value2: ";
         cin >> value2;
         if (value2 == "|")  
         { break; }
         cout << "Value1 is: " << value1 << " and Value2 is: " << value2 << "\n";          
} 

}

[farmerdwight]

I guess I got fixated on having to use an integer to accept numbers. Thanks for your help.

[farmerdwight]

Actually, I'm still needing a different solution. I'm specifically needing to read in two integers. And I will need to be comparing the size of the integers. So I don't think strings will work. Any suggestions?

[LendraDwi]

Hows this ? http://www.cplusplus.com/reference/string/stoi/

[andywestken]

See Bazzy's article for assorted ways to convert strings to numbers, inc. std::stoi as suggested by LendraDwi.

Converting numbers to strings and strings to numbers
http://www.cplusplus.com/articles/D9j2Nwbp/

You might also think about how to handle the errors caused by a user entering random strings (for example, std::stoi will throw an exception if it can't convert the string to a number.)

Andy

[farmerdwight]

Using stoi does seem to work pretty well so thanks for that. I used this line of code to convert the strings to integers and it works good I'd say.

TBO, it still feels like a hack or less elegant than I would like but maybe this is the only way, who knows. I'm also suspicious because my book has been carefully going over new concepts and we haven't covered this function.

cout << "Value1 + Value2 is: " << std::stoi(value1, nullptr, 0) + std::stoi(value2, nullptr, 0) << "\n";

[andywestken]

An up to date book should cover std::stoi() -- it is one of a related set of conversions functions which was introduced in C++11.

As it stands, it is a bit hacky. You ideally need to check the value you get from the user and then give them a chance to correct their mistake.

To make your code robust, the first step is to refactor the code to use a function to read the int value (I started off from newbiee999's code above, but value1 and value2 are now back to ints.)

#include "std_lib_facilities.h"

bool get_int_value(const string& prompt, int& value);

int main()
{
    int value1 = 0;
    int value2 = 0;

    bool more = 0; // "continue" is a keyword
    do
    {
        more = get_int_value("Input value1", value1);
        if(more)
            more = get_int_value("Input value2", value2);
        if(more)
            cout << "Value1 is: " << value1 << " and Value2 is: " << value2 << "\n";          
    }
    while(more);

    return 0;
}

bool get_int_value(const string& prompt, int& value)
{
    cout << prompt << ": ";
    string str;
    cin >> str;
    if (str == "|")
        return false;
    value = stoi(str, nullptr, 0);
    return true;
}

As it stands, the code can't handle bad input, e.g.

Input value1: 1
Input value2: 2
Value1 is: 1 and Value2 is: 2
Input value1: 3
Input value2: a
terminate called after throwing an instance of 'std::invalid_argument'
  what():  stoi

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

(this test app was built with the MinGW version of GCC 4.8.1)

But by adding some exception handling code and a while loop to get_int_value()

bool get_int_value(const string& prompt, int& value)
{
    while(true)
    {
        cout << prompt << ": ";
        string str;
        cin >> str;
        if (str == "|")
            return false;
        try
        {
            value = stoi(str, cha, 0);
            return true;
        }
        catch(invalid_argument)
        {
            cout << "Error: Invalid value. Please enter either\n"
                    "a valid integer value or | to quit.\n";
        }
    }
}

It can now handles the error that cause grief above:

Input value1: 1
Input value2: 2
Value1 is: 1 and Value2 is: 2
Input value1: 3
Input value2: a
Error: Invalid value. Please enter either
a valid integer value or | to quit.
Input value2: 4
Value1 is: 3 and Value2 is: 4
Input value1: |

But get_int_value() is still incomplete...

Input value1: 1
Input value2: 2
Value1 is: 1 and Value2 is: 2
Input value1: 3apples
Input value2: 4pears
Value1 is: 3 and Value2 is: 4
Input value1: 3.1415
Input value2: 2.5
Value1 is: 3 and Value2 is: 2
Input value1: a
Error: Invalid value. Please enter either
a valid integer value or | to quit.
Input value1: 3 a
Input value2: Error: Invalid value. Please enter either
a valid integer value or | to quit.
Input value2: a 3
Error: Invalid value. Please enter either
a valid integer value or | to quit.
Input value2: Value1 is: 3 and Value2 is: 3
Input value1: 12345678910121212
terminate called after throwing an instance of 'std::out_of_range'
  what():  stoi

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

- modifying get_int_value() to reject "3apples", 3.1415, etc requires the second parameter of std::stoi to be checked (to see how much of the string was converted.)

- the function needs to be modified so it doesn't extract both numbers from one input line

- handling the std::out_of_range exception as well will protect the code against overlarge numbers.

Andy

[farmerdwight]

Awesome, thanks for your help and insight.