C++ MFC Converting part of string array into one integer

Question

Here is the problem. I'm trying to write a calculator similar to one that is in all computers. It should take values from one EditBox, make all needed calculations, and then display in another EditBox. For example: 3*6/2; result: 9; I've managed to do this:

double rezultatas = 0;
double temp = 0;
// TODO: Add your control notification handler code here
UpdateData(TRUE);
for (int i = 0; i < seka_d.GetLength(); i++)
{
    if (seka_d[i] == '/' || seka_d[i] == '*')
    {
        if (seka_d[i] == '*')
        {
            temp = (seka_d[i - 1] - '0') * (seka_d[i + 1] - '0');
        }
        if (seka_d[i] == '/')
        {
            temp = (seka_d[i - 1] - '0') / (seka_d[i + 1] - '0');
        }
        //temp = (seka_d[i - 1] - '0') / (seka_d[i + 1] - '0');

    }
    if (seka_d[i] == '+' || seka_d[i] == '-')
    {
        if (seka_d[i] == '-')
        {
            temp = (seka_d[i - 1] - '0') - (seka_d[i + 1] - '0');
        }
        if (seka_d[i] == '+')
        {
            temp = (seka_d[i - 1] - '0') + (seka_d[i + 1] - '0');
        }
        //temp = (seka_d[i - 1] - '0') + (seka_d[i + 1] - '0');

    }
    if (seka_d[i] == '-')
    {
        temp = (seka_d[i - 1] - '0') - (seka_d[i + 1] - '0');
    }

    //rezultatas++;
}
result_d = temp;
UpdateData(FALSE);

It checks string seka_d for any simbols like '*','-','/','+' and the does the operation with two neighbor simbols(ex. 1+2, sums 1 and 2)(i know it doesnt work properly with multiple operations yet), but now I have to also operate with doubles, so I want to know is it possible to convert a part of string to an integer or double(ex. 0.555+1.766). Idea is to take part of string from start to a symbol(from start until '+') and from symbol to an end of string or another symbol(ex. if string is 0.555+1.766-3.445 it would take a part of string from '+' until '-'). Is it possible to do it this way?

This question is not related to MFC technology, so I removed that tag, and added another more appropriate for the question. — Dialecticus
– Dialecticus, Commented Sep 25, 2015 at 10:49

Barmak Shemirani · Accepted Answer · 2015-09-25 19:15:40Z

You can use CString::Tokenize https://msdn.microsoft.com/en-us/library/k4ftfkd2.aspx

or convert to std::string

std::string s = seka_d;

Here is MFC example:

void foo()
{
    CStringA str = "1.2*5+3/4.1-1";
    CStringA token = "/+-*";

    double result = 0;
    char operation = '+'; //this initialization is important
    int pos = 0;
    CStringA part = str.Tokenize(token, pos);
    while (part != "")
    {
        TRACE("%s\n", part); 
        double number = atof(part);

        if (operation == '+') result += number;
        if (operation == '-') result -= number;
        if (operation == '*') result *= number;
        if (operation == '/') result /= number;

        operation = -1;
        if (pos > 0 && pos < str.GetLength())
        {
            operation = str[pos - 1];
            TRACE("[%c]\n", operation);
        }

        part = str.Tokenize(token, pos);
    }

    TRACE("result = %f\n", result);
}

Note, this doesn't handle parenthesis. For example a*b+c*d is ((a*b)+c)*d Window's calculator does the same thing.

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