Operator precedence in Go - Mini Project: Build & Apply

Operator precedence

📖 Scenario: Imagine you are calculating the total cost of items in a shopping cart with discounts and taxes. You need to understand how Go handles operator precedence to get the correct total.

🎯 Goal: Build a simple Go program that calculates the final price of an item after applying a discount and adding tax, using operator precedence correctly.

📋 What You'll Learn

Create variables for price, discount, and tax rate with exact values

Create a variable for discounted price using subtraction and multiplication

Calculate the final price by adding tax to the discounted price using correct operator precedence

Print the final price

💡 Why This Matters

🌍 Real World

Calculating prices with discounts and taxes is common in shopping and billing systems.

💼 Career

Understanding operator precedence helps avoid bugs in financial calculations and data processing.

1

Create initial price variables

Create three variables in Go: price with value 100.0, discount with value 0.2, and taxRate with value 0.1. Use type float64 for all.

Go

// Your code here

Hint

Use var keyword to declare variables with type float64.

2

Calculate discounted price

Add a variable discountedPrice that calculates the price after discount using the formula price - price * discount.

Go

package main

import "fmt"

func main() {
    var price float64 = 100.0
    var discount float64 = 0.2
    var taxRate float64 = 0.1

    // Your code here
}

Hint

Remember multiplication happens before subtraction.

3

Calculate final price with tax

Create a variable finalPrice that adds tax to the discounted price using the formula discountedPrice + discountedPrice * taxRate.

Go

package main

import "fmt"

func main() {
    var price float64 = 100.0
    var discount float64 = 0.2
    var taxRate float64 = 0.1

    var discountedPrice float64 = price - price * discount

    // Your code here
}

Hint

Multiplication happens before addition, so no parentheses needed.

4

Print the final price

Use fmt.Printf to print the finalPrice with two decimal places, using the format string "Final price: %.2f\n".

Go

package main

import "fmt"

func main() {
    var price float64 = 100.0
    var discount float64 = 0.2
    var taxRate float64 = 0.1

    var discountedPrice float64 = price - price * discount
    var finalPrice float64 = discountedPrice + discountedPrice * taxRate

    // Your code here
}

Hint

Use fmt.Printf with "%.2f" to format the float with two decimals.

Practice

1. In Go, which operator has the highest precedence among these: +, -, *, /?

easy

A. Subtraction (-)

B. Addition (+)

C. All have the same precedence

D. Multiplication (*) and division (/)

Solution

1. Step 1: Recall operator precedence rules in Go

   Multiplication (*) and division (/) have higher precedence than addition (+) and subtraction (-).

2. Step 2: Compare given operators

   Among the given operators, * and / are evaluated before + and -.

3. Final Answer:

   Multiplication (*) and division (/) -> Option D

4. Quick Check:

   *, / > +, - [OK]

Hint: Remember: multiply/divide before add/subtract [OK]

Common Mistakes:

• Thinking all operators have equal precedence
• Confusing addition with multiplication precedence
• Ignoring division operator precedence

2. Which of the following Go expressions is syntactically correct and respects operator precedence?

easy

A. result := 5 + (3 * 2

B. result := 5 + * 3 2

C. result := 5 + 3 * 2

D. result := 5 + 3 * * 2

Solution

1. Step 1: Check each expression for syntax correctness

   result := 5 + 3 * 2 uses valid operators and correct syntax. Options B, C, and D have syntax errors like misplaced operators or missing parentheses.

2. Step 2: Confirm operator precedence in result := 5 + 3 * 2

   Multiplication (*) happens before addition (+), so expression is valid and respects precedence.

3. Final Answer:

   result := 5 + 3 * 2 -> Option C

4. Quick Check:

   Valid syntax and precedence in result := 5 + 3 * 2 [OK]

Hint: Check for misplaced or missing operators and parentheses [OK]

Common Mistakes:

• Using two operators in a row without operand
• Missing closing parentheses
• Confusing operator placement

3. What is the output of this Go code?

package main
import "fmt"
func main() {
    x := 2 + 3 * 4 - 6 / 2
    fmt.Println(x)
}

medium

A. 11

B. 10

C. 12

D. 14

Solution

1. Step 1: Apply operator precedence to expression

   Multiplication and division first: 3 * 4 = 12, 6 / 2 = 3.

2. Step 2: Calculate addition and subtraction left to right

   Expression becomes 2 + 12 - 3 = 14 - 3 = 11.

3. Final Answer:

   11 -> Option A

4. Quick Check:

   2 + (3*4) - (6/2) = 11 [OK]

Hint: Do * and / before + and -, then left to right [OK]

Common Mistakes:

• Adding before multiplying
• Subtracting before division
• Ignoring left-to-right evaluation for + and -

4. Identify the error in this Go code snippet related to operator precedence:

package main
import "fmt"
func main() {
    result := 10 / 2 * 3
    + 4 - 1
    fmt.Println(result)
}

medium

A. Line break splits expression incorrectly without continuation

B. Division operator has lower precedence than multiplication

C. Missing parentheses around addition and subtraction

D. Using + and - operators together causes syntax error

Solution

1. Step 1: Check expression syntax across lines

   The expression is split across two lines without proper continuation, causing a syntax error.

2. Step 2: Understand Go line continuation rules

   Go requires expressions split across lines to be clearly continued, usually by operators at line end or parentheses.

3. Final Answer:

   Line break splits expression incorrectly without continuation -> Option A

4. Quick Check:

   Line breaks need proper continuation [OK]

Hint: Avoid breaking expressions without operators or parentheses [OK]

Common Mistakes:

• Assuming operator precedence causes error
• Thinking + and - together cause syntax error
• Ignoring Go's line continuation rules

5. Given the Go expression:

result := 8 + 2 * (5 - 3) / 2 - 1

What is the correct value of result after evaluation?

hard

A. 8

B. 9

C. 10

D. 11

Solution

1. Step 1: Evaluate parentheses first

   (5 - 3) = 2.

2. Step 2: Apply multiplication and division left to right

   2 * 2 = 4, then 4 / 2 = 2.

3. Step 3: Perform addition and subtraction left to right

   8 + 2 = 10, then 10 - 1 = 9.

4. Final Answer:

   9 -> Option B

5. Quick Check:

   8 + 2*(2)/2 - 1 = 9 [OK]

Hint: Calculate parentheses first, then * /, then + - left to right [OK]

Common Mistakes:

• Ignoring parentheses priority
• Doing addition before multiplication
• Dividing before multiplying inside parentheses