Formula string conversion

This is a discussion on Formula string conversion within the C++ Programming forums, part of the General Programming Boards category; Hey, Im writing a program in which i would like the user to be able to enter a formula then ...

  1. #1
    Registered User
    Join Date
    Mar 2002
    Posts
    27

    Formula string conversion

    Hey,
    Im writing a program in which i would like the user to be able to enter a formula then have the formula calculated. The only way i can think of doing this is to have the formula imputted into a string, then use a switch and some loops to execute the formula. Is there a library or a more elegant method to do this?

    Thak you,
    Gr3g

  2. #2
    kmaz
    Guest
    I'm pretty sure there is no simple way to do this, but with classes/objects you would be able to do it probably in a cool way.

  3. #3
    Unregistered
    Guest
    have the user enter the expression in postfix

    Code:
    char array[MAX];
    char ch;
    int i=0;
    while (ch=(char) getc(stdin)){
    array[i]=ch;
    }
    
    int pop(int a)
    {
    return array[a];
    }
    
    void push(int b)
    {
    array[countvar]=b;
    }

    the basic idea is this: if the element is a number, pop it from the stack. If it is an operand, then add/sub/mult/divide the two numbers popped from the stack and push the result.

    Here is an example: 67+12++ (this is 6+7+1+2)
    the program pops 6 and 7, sees the +, adds 6+7, and pushes 13 so the resulting expr is 1312++, which evaluates to 133+, which evaluates to 16.

    In reality it is harder, because you will have to deal with conversions. Also, it is nice if you incorporate the whole thing into a struct or class, and make pop and push private functions. That way it is easier to have a countvar that keeps track of where you are in the stack.

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