# How can I evaluate an expression using sin, cos and other functions?

After some research, I learned about postfix notation and how to parse an expression.

My code converts to postfix notation and then evaluates it using a stack based method. For example:

```
Initial expression: 5 + 2^(4 - 1)
Postfix notation: 5 2 4 1 - ^ +
Result: 13
```

Now I'm trying to expand this program to be able to evaluate expressions with functions such as sin, cos, log, for example `5 + sin (2 + log (2))`

. My initial idea was that before parsing it, find these functions, evaluate their results, and replace them in a string. But I don't think this is a very good idea ...

So how can I do this in an efficient way?

Here is the code written in C # if used: http://pastebin.com/7wB81fyQ , but I would prefer some pseudocode, so I understand that I write better ... I'm not the kind of guy to just copy and insert.

source to share

Treat these functions as you would any other operator, as well as curly braces. Calculate what's in curly braces first, then execute the function.

```
Initial: 3 * Sin(4 + 5)
Postfix: 4 5 + Sin 3 * (that how I would enter it in a HP calculator)
or: 3 4 5 + Sin *
```

Except `+`

which consumes two numbers, `Sin`

consumes only one number.

source to share