How to put if condition on a specific word in input

Question

suppose in the text box I write "add 2 and 3" then the output should be the sum and if I write "subtract 2 from 3" then the output should be the subtraction. then how to put the condition on the words add and subtract ?

Answer 1

in which language?
in PHP you can use strpos and check if it's return value is not false (!==).

Answer 2

in c#