Constants in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of constant iota usage

What is the output of this Go program?

Go

package main
import "fmt"
const (
  a = iota
  b
  c = 5
  d
  e = iota
)
func main() {
  fmt.Println(a, b, c, d, e)
}

A 0 1 5 5 4

B 0 1 5 5 5

C 0 1 5 6 4

D 0 1 5 6 5

💡 Hint

Remember that iota increments on each line, but explicit assignments reset it.

iota starts at 0 for 'a', increments by 1 for 'b'. 'c' is explicitly 5, so 'd' repeats 5. 'e' resumes iota counting from the line number, which is 4.

❓ Predict Output

intermediate

Constant expression evaluation

What will this Go program print?

Go

package main
import "fmt"
const (
  x = 3
  y = x * 2
  z = y + 4
)
func main() {
  fmt.Println(x, y, z)
}

A 3 6 10

B 3 6 7

C 3 5 9

D 3 6 12

💡 Hint

Constants can be expressions using other constants.

x is 3, y is 3*2=6, z is 6+4=10.

❓ Predict Output

advanced

Constant block with mixed types

What is the output of this Go program?

Go

package main
import "fmt"
const (
  a = 1
  b
  c = "hello"
  d
  e = 3.14
  f
)
func main() {
  fmt.Printf("%v %v %v %v %v %v", a, b, c, d, e, f)
}

A 1 2 hello hello 3.14 3.15

B 1 1 hello hello 3.14 3.14

C 1 1 hello hello 3.14 0

D 1 1 hello hello 3.14 <nil>

💡 Hint

Constants repeat the previous value if no new value is given.

b repeats a's value 1, d repeats c's value "hello", f repeats e's value 3.14.

❓ Predict Output

advanced

Using iota with bit shifting

What does this Go program print?

Go

package main
import "fmt"
const (
  _ = 1 << (iota * 2)
  A
  B
  C
)
func main() {
  fmt.Println(A, B, C)
}

A 2 8 32

B 1 4 16

C 4 16 64

D 0 4 16

💡 Hint

iota starts at 0, but the first constant is ignored with underscore.

The first line sets _ = 1 << (0*2) = 1, ignored. Then A = 1 << (1*2) = 4, B = 1 << (2*2) = 16, C = 1 << (3*2) = 64.

🧠 Conceptual

expert

Why are constants preferred over variables for fixed values?

Which is the best reason to use constants instead of variables for fixed values in Go?

A Constants allow dynamic typing which variables do not.

B Constants use less memory than variables because they are stored on the stack.

C Constants can be changed during program execution for flexibility.

D Constants improve code readability and prevent accidental changes at runtime.

💡 Hint

Think about safety and clarity in code.

Constants cannot be changed after compilation, which helps avoid bugs and makes code easier to understand.