How Do I Translate This Algebraic Expression In C++?

Question

I need to write and execute a program in C++ that computes the value of the expression:

5x^2 + 12y / 3x , Where x = 12, And y = 9.8

This is what I have:

int num1 = 12; float num2 = 9.8; float totalResult;
totalResult = 5 * num1 * num2 + 12 * num2 / 3 * num1;

cout << totalResult;

The answer is 23.2667 but I'm getting a wrong result.

Answer 1

Your issue is order of operations (and a typo on num1 * num2).

Your proposed correct answer is 23.2667, which is only possible if you interpret / as being the last operation. To force the division to happen last, put the left and right sides in parentheses:

totalResult = (5 * num1 * num1 + 12 * num2) / (3 * num1);

That way it executes in this order:

                 1      2      4    3       6    5
totalResult = (5 * num1 * num1 + 12 * num2) / (3 * num1);

Otherwise, it was executing in this order:

                1      2      6    3      4   5
totalResult = 5 * num1 * num1 + 12 * num2 / 3 * num1;

Here's a proof with JavaScript:

var num1 = 12; var num2 = 9.8; 
var totalResult = (5 * num1 * num1 + 12 * num2) / (3 * num1);
console.log(totalResult);

Operator Precedence Reference