How do I compare strings correctly?

[neowoot]

Hi all!

Part of my program asks the user to input a number between 1 and 100.
If the number is not between 1 and 100, the program displays an error and asks them to re-enter the number.
I want it set as a string, especially so that if they enter a letter, the program will continue to function correctly.
The problem is that the compiler does not like that I'm using the greater than/less than operators to compare strings. It is fine if I use them for integers, but for strings, it gives me an error.

The error is:
no match for 'operator<' in 'number < 0'

Can anyone offer insight on how I can successfully compare strings? Thank you.

int compare(string number)
{
        while (number < 0 || number > 100)
        {
             system("CLS");
             cout << "\n\n\n\n\n\n\n\n\n\n\n\n\n";
             cout << "\t\t\t\t  "
                  << number << " is invalid!";
             cout << "\n\t\t   Please enter a value in the range 1-100: ";
             cin >> number;
             cout << "\n\n\n\n\n\t\t"; 
        }   
}    

[mobat]

#include <iostream>
#include <string>
#include <stdlib.h>

using namespace std;

int compare(int number)
{
        //loop until a valid score is entered...
        while (number < 0 || number > 100)
        {
             system("CLS");
             cout << "\n\n\n\n\n\n\n\n\n\n\n\n\n";
             cout << "\t\t\t\t  "
                  << number << " is invalid!";
             cout << "\n\t\t   Please enter a value in the range 1-100: ";
             cin >> number;
             cout << "\n\n\n\n\n\t\t";
        }
}


int main()
{
    int number;
    cout << "Enter a number between 1 - 100: ";
    cin >> number;
    compare(number);
}

[Moschops]

A C++ string can be compared with the == operator, as well as the < and > operator. However, they can only be compared with other strings; you are comparing a string to a number, unless you write your own operators for what you want to do.

http://www.cplusplus.com/reference/string/operators/

However, since you're examining a number, why not make number an int, rather than a string? Then you can use the < and > operators as you are at the moment.

[Zeillinger]

@mobat, compare should return an integer.
@neowoot, You can't compare a string and an integer (this isn't the same as comparing strings). You should probably use an integer as @mobat did but you can still get a string from the input and use a string for other functions, just convert the input from string to int^[1] before giving it as a parameter to compare.

[1] http://www.cplusplus.com/forum/general/13135/

[mobat]

You can change it to a void, or you can just do return number;

[lnk2019]

I think you are looking for the string::compare(...) method (see: http://www.cplusplus.com/reference/string/string/compare/).

This function returns 0 if the two strings are the same, greater than 0 if the string being compared is greater than the string given as parameter and vice-versa.

I hope this helps!

EDIT: I might have misinterpreted the question.

You may want to convert the string into an integer then use this integer with the < > symbols.

Although I've not tried it, I have a sneeky suspicion that the string::compare(...) method will work but you'll have to test it for yourself and see.

Example:

while ( number.compare("0") > 0 || number.compare("100") < 0 )
{
    //your code here
}

[Duthomhas]

FWIW, you actually can compare two strings as numeric values, so long as they have the same sign and the same number of digits (add leading zeros as needed).