Constants in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a constant named Pi with the value 3.14.

Go

const Pi [1] 3.14

Drag options to blanks, or click blank then click option'

A=

B:=

C==

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using := instead of = for constants

Using == which is a comparison operator

In Go, constants are declared using the const keyword followed by the name, then an equals sign =, and the value.

2fill in blank

medium

Complete the code to declare multiple constants Pi and E with values 3.14 and 2.71.

Go

const (
    Pi [1] 3.14
    E  [1] 2.71
)

Drag options to blanks, or click blank then click option'

A:=

B==

C=

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using := inside const blocks

Using : instead of =

When declaring multiple constants in a block, each constant uses an equals sign = to assign its value.

3fill in blank

hard

Fix the error in the constant declaration to assign the value 100 to MaxScore.

Go

const MaxScore [1] 100

Drag options to blanks, or click blank then click option'

A:=

B=

C==

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using := instead of =

Using == which causes syntax errors

Constants must be assigned with =. The short declaration := is only for variables.

4fill in blank

hard

Fill both blanks to declare constants Width and Height with values 1920 and 1080.

Go

const Width [1] 1920
const Height [2] 1080

Drag options to blanks, or click blank then click option'

A=

B:=

C==

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using := for constants

Using : or == instead of =

Each constant declaration uses = to assign its value.

5fill in blank

hard

Fill all three blanks to declare constants Name, Age, and Active with values "Alice", 30, and true.

Go

const Name [1] "Alice"
const Age [2] 30
const Active [3] true

Drag options to blanks, or click blank then click option'

A=

B:=

C==

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using := for constants

Using == or : instead of =

Each constant declaration uses = to assign its value, regardless of type.

Practice

1. What is the purpose of using const in Go programming?

easy

A. To declare a value that cannot be changed

B. To declare a variable that can change

C. To create a function

D. To start a loop

Solution

1. Step 1: Understand the role of const

   The const keyword is used to declare constants, which are fixed values that cannot be changed after being set.

2. Step 2: Compare options with the definition

   To declare a value that cannot be changed correctly states that const declares a value that cannot be changed, while other options describe unrelated concepts.

3. Final Answer:

   To declare a value that cannot be changed -> Option A

4. Quick Check:

   Constants = fixed values [OK]

Hint: Constants hold fixed values, variables do not change [OK]

Common Mistakes:

• Confusing constants with variables
• Thinking const declares functions
• Assuming const starts loops

2. Which of the following is the correct way to declare a constant named Pi with value 3.14 in Go?

easy

A. const Pi = 3.14

B. let Pi = 3.14

C. Pi := 3.14

D. var Pi = 3.14

Solution

1. Step 1: Recall Go syntax for constants

   In Go, constants are declared using the const keyword followed by the name and value.

2. Step 2: Identify the correct syntax

   const Pi = 3.14 uses const Pi = 3.14, which is the correct syntax. Options A and C declare variables, and B uses invalid Go syntax.

3. Final Answer:

   const Pi = 3.14 -> Option A

4. Quick Check:

   const keyword = correct declaration [OK]

Hint: Use const keyword for fixed values, not var or := [OK]

Common Mistakes:

• Using var or := instead of const
• Using let which is not Go syntax
• Missing the const keyword

3. What will be the output of this Go program?

package main
import "fmt"
const greeting = "Hello"
func main() {
    fmt.Println(greeting)
}

medium

A. greeting

B. Compilation error

C. Hello\n

D. Hello

Solution

1. Step 1: Understand constant usage in the program

   The constant greeting is declared with value "Hello" and printed in main.

2. Step 2: Predict the output of fmt.Println

   fmt.Println(greeting) prints the string value of the constant, which is "Hello" without quotes.

3. Final Answer:

   Hello -> Option D

4. Quick Check:

   Printing constant value = Hello [OK]

Hint: Print constant name to get its fixed value output [OK]

Common Mistakes:

• Expecting the name 'greeting' to print
• Thinking it prints with quotes
• Assuming a compile error

4. Identify the error in this Go code snippet:

package main
import "fmt"
const x = 10
func main() {
    x = 20
    fmt.Println(x)
}

medium

A. Variable 'x' not declared

B. Cannot assign to constant 'x' after declaration

C. Missing import of fmt package

D. No error, code runs fine

Solution

1. Step 1: Check constant reassignment

   The code declares x as a constant with value 10, then tries to assign 20 to it, which is not allowed.

2. Step 2: Verify other possible errors

   There are no other compilation errors; the only issue is reassignment of the constant.

3. Final Answer:

   Cannot assign to constant 'x' after declaration -> Option B

4. Quick Check:

   Constants cannot be reassigned [OK]

Hint: Constants cannot be changed after declaration [OK]

Common Mistakes:

• Trying to assign new value to a constant
• Ignoring missing imports
• Confusing constants with variables

5. Given the following Go code, what will be the output?

package main
import "fmt"
const (
    A = iota
    B
    C = 5
    D
)
func main() {
    fmt.Println(A, B, C, D)
}

hard

A. 0 1 2 3

B. 0 1 5 5

C. 0 1 5 3

D. Compilation error due to iota usage

Solution

1. Step 1: Understand iota behavior in constant blocks

   iota starts at 0 and increments by 1 for each line unless overridden.

2. Step 2: Analyze each constant value

   A = iota (0), iota increments to 1; B = iota (1), iota to 2; C = 5 (explicit), iota to 3; D = iota (3).

3. Step 3: Confirm output

   Printing A, B, C, D outputs: 0 1 5 3

4. Final Answer:

   0 1 5 3 -> Option C

5. Quick Check:

   iota increments except when overridden [OK]

Hint: iota increments unless constant value is explicitly set [OK]

Common Mistakes:

• Assuming D equals C's value (5)
• Thinking iota resets after explicit value
• Expecting compilation error