Novice C ++ practice project - Calculator

This blog is used to record a calculator for my own use C ++ implementation, the goal is to complete the four arithmetic operations with parentheses, and optimized at a later stage with the factory design pattern.

 

 

Part 1：calculate 1+1=2

To achieve such a calculation formula, you only need to use a string split, initially tried stringstream to first read a whole string of "1 + 2", and then create two temporary variables int and a char, >> read into use, but found reading in the middle of char is ignored

string s ="12+34";
    //    stringstream ss(s);
        //    int n1,n2,c;
    //    ss>>n1>>c>>n2;//c is 34 ,the '+' is ignored

I then to switch to the substr dividing, substr two parameters, the beginning of a string separated position and the other is the length of the string, the second parameter is the default value NPoS, i.e. end of the string.

    int i =0;
    while(isdigit(s[i]))
    {
        ++i;//pos
    }
    //    int n =atof("22.0");
    //    cout<<n;
    //float d = atof(s.substr(0,i).c_str());
    cout<<cal( atof(s.substr(0,i).c_str()) , atof(s.substr(i+1).c_str()) ,s[i])<<endl;
　　
　　//string to const char*
　　//use c_str() 函数

Such a simple run out of 1 + 1 = 2 a! But this procedure to change a lot of trouble, there is no way to adapt to 1 + 1 + 1 = 3, there is no priority operation, wait for the next part we come back to do new features.