kumar310

Hello Everyone,

I need some help on some HW. I normally don't ask for help about hw but this assignment pretty much determines my grade. Im not asking for you guys to do it for me but I just need a little direction please. My teacher wants me to do the following:

Design and build a parsing calculator. My program must

accept a string of the form 12 * 3 / (123 + 4) ,
do the specified calculation, and
display the result.

The program should continue to ask for input until the user decides to quit.

In addition, this program must use a stack to implement the calculation. You’ll have to

accept the input as a character string,
break it up into its component parts, and
convert it to numbers and operators, and
do the calculation.Notes:

1. Instead of the usual precedence, evaluate expressions from left
to right, but make sure that operations done inside parentheses
are done first. For example, the expression 22 * 3 + ( 2 * 3) ,
should be evaluated:
22 * 3 + ( 6) 66 + 6 72
2. Look up and use the following standard library functions to help with your design:

char* strtok(char*, char*)
double atof(char*)
Please I need some direction !

Kumar

DaWei

That's a pretty detailed set of instructions. Have you been paying attention in class?

See input functions such as fgets, which you would couple with the required strtok. It seems that atof is a requirement, so use that, but be aware that things like strtol should be used in actual practice.

Once you have looked up those functions, go through your problem line by line, with pencil and paper, design your solution, code it, and ask here for help with the problems.

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mjbeam

I would try creating a recursive class. Send the string to the class. In the class, parse the string from left to right and push each number and operator onto the stack. When you come to a parentheses, scan the string until you find the last closing parentheses and call the class again (from within the class, this is the recursive part) with everything between the opening and closing parentheses (the return value will be a number). Then, pop each item and operator one at a time from the stack performing the operations as you go. When the stack is empty, return the number.

-Mike

DaWei

I'm thinking that you aren't ready for recursion. If you were, this post would probably not have been made.

I could be wrong. For an example of recursion, see here: recursion.

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Jessehk

DaWei: hehe

I did this exact thing in O'Caml. http://www.programmingforums.org/thread13332.html
I wouldn't expect you to understand the code (O'Caml is a wacky language), but because there is pattern-matching, it might be kind-of readable.
Specifically, I think this was the latest version: http://www.programmingforums.org/att...9&d=1182313872

eval.ml, the file where I actually evaluated the tokens, might be useful.
I should warn you though: I'm a beginner and I might not have done things in an optimal way.

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