Learning Shunting yard algorithms

I am making a calculator like CalcX and for that i need to find a way to teach computer PEDMAS

we think of
4 + 18/(9-3)
as
4 + 18 / 6
4 + 3
7

But how will a computer decided it??

Thats where the Shunting yard Algorithm comes.. it utilises stack and queue.. that soo lit

Qalc : MY inspiration