How to extract numbers used in string?

Question

I've got a std::string number = "55353" and I want to extract the numbers that I've used in this string (5 and 3). Is there a function to do that? If so, please tell me it's name, I've been searching for quite a while now and still haven't found it... UPD: I've solved my problem (kinda)

std::string number(std::to_string(num));

std::string mas = "---------";              

int k = 0;                                  
for (int i = 0; i < number.size(); i++) {
    char check = number[i];                 
    for (int j = 0; j < mas.size(); j++) {
        if (check == mas[j])                
            break;                          
        if (check != mas[j] && check != mas[j+1]) {
            mas[k] = check;                 
            k++;                            
            break;                          
        }                                   
    }                                       
}                                           

mas.resize(k); mas.shrink_to_fit();

std::string mas will contain numbers that were used in std::string number which is a number converted to std::string using std::to_string().

No, there's no standard function for doing this. You'll have to write it yourself. — Pete Becker, Mar 20 '16 at 20:25
How do I do it then? I've tried so much stuff, but it just won't work. I'm new to C++, please help. — Michael, Mar 20 '16 at 20:26
Best option to stop being new to C++ is to learn. See [The Definitive C++ Book Guide and List](http://stackoverflow.com/q/388242/1889329) for inspiration. — IInspectable, Mar 20 '16 at 20:28
You've asked a question but not shown any code that attempts to solve it. So the next step should be obvious: write some code, using the hing that @juanchopanza gave you. — Pete Becker, Mar 20 '16 at 20:51

score 0 · Answer 1 · answered Mar 20 '16 at 22:00

Try this:

std::string test_data= "55335";
char digit_to_delete = '5';
unsigned int position = test_data.find();
test_data.erase(position, 1);
cout << "The changed string: " << test_data << "\n";

The algorithm is to find the number (as a character) within the string. The position is then used to erase the digit in the string.

score 0 · Answer 2 · answered Mar 21 '16 at 00:35

Your question looks like homework, so I can guess what you forgot to tell us.

mas starts with ten -. If you spot a 5, you should replace the 6th (!) dash with a '5'. That "6th" is just an artifact of English. C++ starts to count at zero, not one. The position for zero is mas[0], the first element of the array.

The one tricky bit is to understand that characters in a string aren't numbers. The proper term for them is "(decimal) digits". And to get their numerical value, you have to subtract '0' - the character zero. So '5' - '0' == 5 - the character five minus the character zero is the number 5.

How to extract numbers used in string?

2 Answers2