How to do math with a single string? (Javascript)

Question

I have a string with a expression, I don't know how many numbers are in the string or what operations to perform, the string contains only numbers and the operations (+-×÷), I want to solve the expression and return the result.

How can I do it?

Answer 1

You could try the eval() function.
See here:
https://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_eval

Answer 2

To convert a string to a number, you can use `parseInt(x, 10)`.

Now, consider the simple case where it's just "+" and nothing else.

In that case you can split your string into an array (`myString.split('+');`), parseInt each element, and then use a loop to sum it all up, left to right.

It gets harder if you have "+" and "-". Not only do you need to split your string, you also need to know whether you found a "+" or a "-". You will have to get creative on that, `myString.split` will probably not work - you can read the string character by character, or you can use regex, or other things.

"*" and "/" are especially interesting because multiplication and division happen before + and -. But turns out it's easy:

First split on +-, to get a list of "sub-problems":

"1+2*3-4/5+6" -> ["1", "2*3", "4/5", "6"]

Then you run through the list and solve the simpler "*/" problems left to right, then you treat the whole thing as a simpler "+-" problem.

I hope this helps, it's a way to tackle the problem incrementally.