How to validate numbers

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3.00/5 (2 votes)

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Right basically I want to know how to declare the program to not screw up when someone enters a character

I thought it might be something like

while( height != 'float')loop etc

but that dose not work and it does screw up. Please help!

Posted 15-Nov-10 10:30am

WurmInfinity

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2 solutions

Solution 1

You could define the rules that define a number and simply create code for that
You would need code to rules like:
1. can start with an optional minus ('-')
2. 1 or more digits ('0'..'9')
3. optional a single dot ('.') and again no 2.

A second option is to consider using a regex expression (this example only accepts digits 0..9).

C#

string Temp = "Hax00r L33t";
string Output = Regex.Replace(Temp, "[^0-9]", "");

Good luck!

Posted 15-Nov-10 10:53am

E.F. Nijboer

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Alain Rist · Accepted Answer · 2010-11-15T23:28:00

Hi,

Keyboard input validation is always a challenge. This function handles some usual cases:

C++

#include <sstream>
template <class Num>
bool Validate(const std::string& input, Num& num)
{
    Num tmp;
    std::istringstream iss(input);
    iss >> std::skipws >> tmp >> std::skipws;
    return iss.eof() && !iss.fail() ? num = tmp, true : false;
}

Check with:

C++

#include <iostream>
int main()
{
    std::string input;
    for (;;)
    {
        std::getline(std::cin, input); // get all input
        int i = 0;
        bool bint = Validate(input, i);
        float f = 0;
        bool bfloat = Validate(input, f);
    }
    return 0;
}

"123", " 123 " "-123" are validated as int and float.
"12 3", " 12 3 " "- 123" are invalidated as int and float.
"123.", " .123 " "-12.3" " -.123e4 " are invalidated as int and validated as float.

cheers,
AR