Converting from string to int with a function

Question

I'm fairly new to programming and I'm trying to get a function working that converts a string to an int. My idea with this function was to collect every number in the string and store it in another string, then convert it to an int.

The function returns the value 0.

What this function is supposed to do is return the converted number. Which should not be 0.

int getNumberFromString(int convertedNumber, string textToConvert)
{
    for (int i = 0; i < textToConvert.size(); i++)
    {
        string collectNumbers;
        int j = 0;
        if (textToConvert[i] == '1' || textToConvert[i] == '2' || textToConvert[i]   == '3' ||
            textToConvert[i] == '4' || textToConvert[i] == '5' || textToConvert[i] == '6' ||
            textToConvert[i] == '7' || textToConvert[i] == '8' || textToConvert[i] == '9' || textToConvert[i] == '0')
        {
            collectNumbers[j] = textToConvert[i];
            j++;
        }
        if (collectNumbers.size() == 0)
        {
            return false;
        }
        else if (collectNumbers.size() > 0)
        {

            stringstream convert(collectNumbers);
            if (!(convert >> convertedNumber))
            {
                convertedNumber = 0;
            }
            return convertedNumber;
        }
    }
}

IF the first character in the input string is not a number return false gets called during the first iteration of the for loop. FWIW There are a lot of other problems with this code. — Captain Obvlious
– Captain Obvlious, Commented Apr 21, 2014 at 22:27
Note in particular that you don't need the loop for a conversion via stringstream, and that the digits 0 through 9 are guaranteed consecutive values (this is not so for the English letters). — Cheers and hth. - Alf
– Cheers and hth. - Alf, Commented Apr 21, 2014 at 22:30
@user2176127 Indeed. My bad - I blame this on C++ deciding to re-use an operator with a totally different meaning than C. — Jonathon Reinhart
– Jonathon Reinhart, Commented Apr 21, 2014 at 22:32

OldSurehand · Accepted Answer · 2014-04-21 22:29:48Z

1

Maybe you should just use library function ?

int stoi (const string&  str, size_t* idx = 0, int base = 10);

answered Apr 21, 2014 at 22:29

OldSurehand

413 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Cheers and hth. - Alf Over a year ago

not all compilers in main use support this function yet.

OldSurehand Over a year ago

Yep, but g++ do with option -std=c++11

Paul Evans · Accepted Answer · 2014-04-21 22:32:31Z

1

You want somehting more like:

int getNumberFromString(int convertedNumber, string textToConvert) {
    int retval = 0;
    for (auto c: textToConvert) {
        retval *= 10;
        retval += c - '0';
    }
    return retval;
}

if you need to code it, or simply use stoi()

answered Apr 21, 2014 at 22:32

Paul Evans

27.7k3 gold badges41 silver badges56 bronze badges

1 Comment

Cheers and hth. - Alf Over a year ago

I would drop the get prefix. getSin(x), ouch.

Mats Petersson · Accepted Answer · 2014-04-21 22:34:12Z

1

Your MAIN problem is that you are trying to convert the number before you have collected all the digits. You should loop over all the digits (use isdigit or if (x >= '0' && x <= '9') to avoid long list of individual digits - or, if you really like to list all digits, use switch to make it more readable).

Once you have collected all the digits, then convert AFTER the loop.

The statement return false, will be the same as return 0; since false will get converted to an integer with the value zero. So you won't be able to tell the difference between reading the value zero from a string and returning false (this is not PHP or JavaScript where type information is included in return values).

answered Apr 21, 2014 at 22:34

Mats Petersson

130k15 gold badges147 silver badges233 bronze badges

1 Comment

user3546673 Over a year ago

I appreciate the help and it makes hell of a lot more sense now, cheers.

Collectives™ on Stack Overflow

Converting from string to int with a function

3 Answers 3

2 Comments

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related