Evaluate equation but ignore order of mathematical operations and parentheses - string

Question

I'm trying to write a function that ignores the order of mathematical operations and parentheses. The function just evaluates operators from left to right. (for +-*/^)
Example 1: 5 - 3 * 8^2 returns 256.
Example 2: 4 / 2 - 1^2 + (5*3) returns 18.
Here's what I did:
function out = calc(num)
[curNum, num] = strtok(num, '+-*/^');
out = str2num(curNum);
while ~isempty(num)
sign = num(1);
[curNum, num] = strtok(num, '+-*/^');
switch sign
case '+'
out = out + str2num(curNum);
case'-'
out = out - str2num(curNum);
case '*'
out = out.*str2num(curNum);
case '/'
out = out./str2num(curNum);
case '^'
out = out.^str2num(curNum);
end
end
end
My function doesn't ignore the left to right rule. How do I correct for this?

Answer 1

Your first example fails because you are splitting the string with the +-*/ delimiters, and you omitted the ^. You should change this to +-*/^ in lines 2 and 6.
Your second example fails because you aren't telling your program how to ignore the ( and ) characters. You should strip them before you enter the switch statement.
curNum = strrep(curNum,'(','')
curNum = strrep(curNum,')','')
switch sign
...

Answer 2

This is a way without any switch statements.
str = '4 / 2 - 1^2 + (5*3)'
%// get rid of spaces and brackets
str(regexp(str,'[ ()]')) = []
%// get numbers
[numbers, operators] = regexp(str, '\d+', 'match','split')
%// get number of numbers
n = numel(numbers);
%// reorder string with numbers closing brackets and operators
newStr = [numbers; repmat({')'},1,n); operators(2:end)];
%// add opening brackets at the beginning
newStr = [repmat('(',1,n) newStr{:}]
%// evaluate
result = eval(newStr)
str =
4/2-1^2+5*3
newStr =
((((((4)/2)-1)^2)+5)*3)
result =
18