Zero values in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a zero value in Go?

A zero value is the default value a variable has when it is declared but not explicitly initialized. It depends on the variable's type.

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What is the zero value of an int in Go?

The zero value of an int is 0.

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What is the zero value of a string in Go?

The zero value of a string is an empty string "".

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What is the zero value of a bool in Go?

The zero value of a bool is false.

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What is the zero value of a pointer type in Go?

The zero value of a pointer is nil, meaning it points to nothing.

What happens if you declare a variable in Go without assigning a value?

A It is automatically assigned 1.

B It causes a compile error.

C It contains random data.

D It gets the zero value of its type.

In Go, variables declared without explicit initialization get the zero value of their type.

What is the zero value of a float64 in Go?

A 1.0

B 0.0

C "" (empty string)

D nil

The zero value of float64 is 0.0.

Which of these is NOT a zero value in Go?

A "0" for string

B 0 for int

C nil for pointer

D false for bool

The zero value for string is an empty string "", not "0".

What is the zero value of a slice in Go?

A An empty slice with length 0

B A slice with one element 0

C nil

D A slice with random values

The zero value of a slice is nil, meaning it points to no underlying array.

Why are zero values useful in Go?

A They prevent variables from having garbage values.

B They make the program slower.

C They force you to always initialize variables.

D They cause runtime errors.

Zero values ensure variables have a safe default value, avoiding unpredictable behavior.

Explain what zero values are in Go and give three examples.

Think about what happens when you declare a variable without setting it.

Why does Go use zero values for uninitialized variables? How does this help programmers?

Consider how zero values affect program reliability.

Practice

1. What is the zero value of an int variable in Go?

easy

A. "" (empty string)

B. nil

C. 0

D. false

Solution

1. Step 1: Understand zero values for basic types

   In Go, each type has a default zero value when not initialized.

2. Step 2: Identify zero value for int type

   The zero value for int is the number 0.

3. Final Answer:

   0 -> Option C

4. Quick Check:

   int zero value = 0 [OK]

Hint: Remember: int zero value is always 0 [OK]

Common Mistakes:

• Confusing int zero value with nil
• Thinking zero value is empty string
• Mixing boolean zero value with int

2. Which of the following is the correct way to declare a variable with its zero value in Go?

easy

A. var x int = false

B. var x int = nil

C. var x int = ""

D. var x int

Solution

1. Step 1: Recall Go variable declaration syntax

   Declaring a variable without initialization sets it to its zero value.

2. Step 2: Check each option for correctness

   var x int declares x as int without initialization, so it gets zero value 0. Other options assign invalid values for int.

3. Final Answer:

   var x int -> Option D

4. Quick Check:

   Declare without init = zero value [OK]

Hint: Declare without assignment to get zero value [OK]

Common Mistakes:

• Assigning nil to int
• Assigning string to int
• Assigning boolean to int

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

package main
import "fmt"
func main() {
    var b bool
    fmt.Println(b)
}

medium

A. false

B. Compilation error

C. nil

D. true

Solution

1. Step 1: Identify the variable type and initialization

   Variable b is declared as bool without explicit initialization.

2. Step 2: Recall zero value for bool type

   The zero value for bool is false, so b is false by default.

3. Final Answer:

   false -> Option A

4. Quick Check:

   bool zero value = false [OK]

Hint: Uninitialized bool defaults to false [OK]

Common Mistakes:

• Expecting true as default
• Thinking nil is valid bool
• Assuming compilation error

4. Identify the error in this Go code snippet related to zero values:

package main
func main() {
    var s string = nil
}

medium

A. Assigning nil to string causes a compile error

B. String zero value should be 0

C. Variable s should be declared as int

D. No error, code runs fine

Solution

1. Step 1: Understand zero value for string type

   Zero value for string is an empty string "", not nil.

2. Step 2: Check assignment validity

   Assigning nil to a string variable causes a compile-time error because nil is not a valid string value.

3. Final Answer:

   Assigning nil to string causes a compile error -> Option A

4. Quick Check:

   string zero value = "" not nil [OK]

Hint: Strings cannot be nil, use empty string "" [OK]

Common Mistakes:

• Using nil for string
• Confusing zero value with nil
• Ignoring compile errors

5. You want to create a map in Go that stores string keys and integer values. You declare it as:

var m map[string]int

What is the zero value of m and what must you do before adding elements?

hard

A. m is zero; no initialization needed, just assign values

B. m is nil; you must initialize it with make before adding elements

C. m is an empty map; you can add elements immediately

D. m is a map with default zero values for keys and values

Solution

1. Step 1: Identify zero value of map type

   Maps declared without initialization have zero value nil.

2. Step 2: Understand map usage requirements

   You cannot add elements to a nil map; you must initialize it using make(map[string]int) before adding keys and values.

3. Final Answer:

   m is nil; you must initialize it with make before adding elements -> Option B

4. Quick Check:

   Maps zero value = nil; initialize with make [OK]

Hint: Maps start nil; use make() before adding keys [OK]

Common Mistakes:

• Trying to add to nil map
• Assuming map is empty but usable
• Confusing zero value with empty map