C++ Numeric Validation - Loop being used

Question

I posted an earlier question asking for help with using a validation script in my code. After a very helpful answer I was able to sort of figure out how I needed to proceed. Well, I've hit a big obstacle;

#include <iostream>
#include <sstream>
#include <string>
#include <ctype.h>

using namespace std;

int main()
{
        unsigned __int64 input = 0;
        int n, i;
        char str[]="c3po...";
        i=1;
        n=0;


        for (cout << "Input a number" << endl; cin >> input; cin.ignore(numeric_limits<int>::max(), '\n'))
    {
        cout << "We're parsing your input '" << input << "'\n";

     if (input % 2 == 0) 
        {
            cout << "Even!" << endl;
        }

    else if (input % 2 == 1)
        {
            cout << "Odd" << endl;
            cout << "Lets make it even shall we? " << "Your new number is... " << input + 1 << endl;
        }
    else (isalnum(str[i]));i++;
        { 
        cout << "We could not parse '" << input << "' as a number.\n";
        }    
    }
    system ("pause");
    return 0;
}

As you can see from my code, the validation script is well, sort of working. I have some bugs I wish to iron out.

1- When I input a number, it runs though the code as it should but it also displays

Could not parse 'inputted number' as a number

obviously when a number is inputted you don't want this to happen!

2- For the error message, it is showing the inputted number as [0]. Is this to do with using an integer? How can this be fixed?

Thanks!

You are not putting in practice what you got for you previous question. You are still extracting directly in input instead of using a variable to validate the user's input. — PRouleau, Nov 19 '12 at 01:13
I couldn't understand that code. I broke it down and changed the layout so it looked like how I would code, but I have no idea what the parts do :( I've kept it, so when I get more experience I will go back to it and modify it. — John Brown, Nov 19 '12 at 07:52
Then rewrite it by using a regular loop or remote it entirely. You basically have two steps: 1) get user input, 2) validate it. I can point two problems: a) you are using isalnum() instead of isalpha() or !isdigit(); b) you are reading directly in "input" which is of type __int64 and so it can only contains a number. Of course, there is also the else-thing. — PRouleau, Nov 20 '12 at 00:25

score 2 · Accepted Answer · answered Nov 19 '12 at 00:26

2

your problem is quite simple, you have small mistake on this line

else (isalnum(str[i]));

Your else statement ends at the semicolon and does actually nothing. Following statements will be executed every time.

i++;
    { 
    cout << "We could not parse '" << input << "' as a number.\n";
    }

answered Nov 19 '12 at 00:26

CodeBro

199
4

Hmm, how would I go across fixing this? – John Brown Nov 19 '12 at 07:52
I think you can just delete it. Statement following else just checks second letter of string in str, since str and i don't change. Since there is no if statement your error message is printed every time. If you want to check if user input was actually a number check out http://stackoverflow.com/questions/4654636/how-to-determine-if-a-string-is-a-number-with-c – CodeBro Nov 19 '12 at 10:47
Is there any way to get it sorted using my own code? I've haven't been doing c++ for very long, so ok trying to get hold of the basics, the link you sent me just seems to go straight over my head! – John Brown Nov 19 '12 at 11:49
There is no point in validating your variable if it is unsigned integer, because it will always contain a valid number whether user gave good or bad input. Doing real validation requires bit more complicated code like the one in the link. – CodeBro Nov 20 '12 at 10:48

C++ Numeric Validation - Loop being used

1 Answers1