Debug.Log for debugging in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Debug.Log statement?

Consider the following Unity C# code snippet. What will be printed in the Console when this runs?

Unity

int score = 10;
Debug.Log($"Player score is: {score}");

A Error: score is not defined

B Player score is: {score}

C Player score is: 0

D Player score is: 10

💡 Hint

Look at how the $ symbol works with strings in C#.

The $ before the string allows embedding variables inside curly braces. So {score} is replaced by the value 10.

❓ Predict Output

intermediate

What does this Debug.Log print?

Look at this code snippet. What will appear in the Unity Console?

Unity

int x = 5;
int y = 3;
Debug.Log("Sum is: " + (x + y));

A Sum is: (x + y)

B Sum is: 8

C Sum is: 53

D Sum is: x + y

💡 Hint

Remember how + works with strings and numbers.

The parentheses force the addition before concatenation, so 5 + 3 = 8, then concatenated to the string.

❓ Predict Output

advanced

What error does this Debug.Log cause?

Examine this code snippet. What error will Unity show in the Console?

Unity

int[] numbers = {1, 2, 3};
Debug.Log(numbers[3]);

A IndexOutOfRangeException

B NullReferenceException

C No error, prints 3

D SyntaxError

💡 Hint

Check the array indices and their valid range.

The array has indices 0,1,2. Accessing index 3 is out of range and causes IndexOutOfRangeException.

❓ Predict Output

advanced

What will this Debug.Log print?

What is the output of this code in the Unity Console?

Unity

string playerName = null;
Debug.Log($"Player: {playerName?.ToUpper() ?? "Unknown"}");

A Player: Unknown

B Player: null

C NullReferenceException

D Player:

💡 Hint

Look at the null conditional operator and null-coalescing operator.

playerName is null, so playerName?.ToUpper() returns null, then ?? "Unknown" replaces null with "Unknown".

❓ Predict Output

expert

What is the output of this Debug.Log with a loop?

Consider this code. What will be printed in the Unity Console?

Unity

for (int i = 0; i < 3; i++)
{
    Debug.Log($"Count: {i}");
}

A

Count: 0
Count: 1
Count: 2
Count: 3

B

Count: 1
Count: 2
Count: 3

C

Count: 0
Count: 1
Count: 2

D Count: 3

💡 Hint

Remember how for loops count from start to less than end.

The loop runs with i = 0,1,2 and prints each value. It stops before i reaches 3.

Practice

1. What is the main purpose of Debug.Log in Unity?

easy

A. To create new game objects

B. To save game data to a file

C. To change the color of objects

D. To print messages to the Console for debugging

Solution

1. Step 1: Understand Debug.Log function

   Debug.Log is used to print messages to the Unity Console, helping developers see what is happening in the game.

2. Step 2: Identify the purpose from options

   Only To print messages to the Console for debugging describes printing messages for debugging, which matches Debug.Log's purpose.

3. Final Answer:

   To print messages to the Console for debugging -> Option D

4. Quick Check:

   Debug.Log prints messages = B [OK]

Hint: Debug.Log shows messages in Console to check game status [OK]

Common Mistakes:

• Thinking Debug.Log creates or changes objects
• Confusing Debug.Log with saving or loading data
• Assuming Debug.Log changes game visuals

2. Which of the following is the correct way to print the message "Hello World" using Debug.Log in Unity?

easy

A. Debug.Log(Hello World);

B. Debug.Log("Hello World");

C. Debug.Log['Hello World'];

D. Debug.Log{Hello World};

Solution

1. Step 1: Check correct syntax for Debug.Log

   Debug.Log requires a string inside parentheses and double quotes for text, like Debug.Log("text").

2. Step 2: Identify correct option

   Debug.Log("Hello World"); uses parentheses and double quotes correctly. Other options have wrong syntax like missing quotes or wrong brackets.

3. Final Answer:

   Debug.Log("Hello World"); -> Option B

4. Quick Check:

   Correct syntax uses parentheses and quotes = D [OK]

Hint: Use parentheses and double quotes for strings in Debug.Log [OK]

Common Mistakes:

• Forgetting quotes around text
• Using square or curly brackets instead of parentheses
• Missing semicolon at the end

3. What will be printed in the Console when this code runs?

int score = 10;
Debug.Log("Score: " + score);

medium

A. Score: 10

B. Score: score

C. 10

D. Score + score

Solution

1. Step 1: Understand string concatenation in Debug.Log

   The code combines the string "Score: " with the integer variable score using +, which converts the number to text.

2. Step 2: Determine the output message

   The output will be the text "Score: " followed by the value 10, so the Console shows "Score: 10".

3. Final Answer:

   Score: 10 -> Option A

4. Quick Check:

   String + int converts int to string = A [OK]

Hint: Adding string + number prints combined text in Console [OK]

Common Mistakes:

• Expecting variable name printed instead of value
• Forgetting + operator for concatenation
• Confusing output with just number or variable name

4. What is wrong with this code snippet?

int score = 10;
Debug.Log("Player score is: " + score)

medium

A. Debug.Log cannot print variables

B. score variable is not declared

C. Missing semicolon at the end

D. Quotes are missing around the string

Solution

1. Step 1: Check syntax of Debug.Log statement

   The statement is missing a semicolon at the end, which is required in C#.

2. Step 2: Verify other parts

   The string has quotes, score variable is declared above, and Debug.Log can print variables. The syntax error is the missing semicolon.

3. Final Answer:

   Missing semicolon at the end -> Option C

4. Quick Check:

   Statements need semicolon ; at end = A [OK]

Hint: Always end Debug.Log lines with a semicolon ; [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Assuming Debug.Log can't print variables
• Confusing string quotes with missing quotes

5. You want to debug a player's health value inside the Update() method. Which code correctly prints the health variable every frame?

hard

A. void Update() { Debug.Log(health); }

B. void Update() { Debug.Log("health"); }

C. void Update() { Debug.Log(health + health); }

D. void Update() { Debug.Log(health); Debug.Log(); }

Solution

1. Step 1: Understand how to print variable value

   To print the value of health, pass it directly to Debug.Log. void Update() { Debug.Log(health); } does this correctly.

2. Step 2: Check other options for correctness

   void Update() { Debug.Log("health"); } prints the word "health" literally, not the variable value. void Update() { Debug.Log(health + health); } incorrectly adds health to itself (doubling the numeric value). void Update() { Debug.Log(health); Debug.Log(); } calls Debug.Log() without arguments, causing error.

3. Final Answer:

   void Update() { Debug.Log(health); } -> Option A

4. Quick Check:

   Pass variable directly to Debug.Log to print value = C [OK]

Hint: Pass variable directly to Debug.Log to see its value [OK]

Common Mistakes:

• Printing variable name as string instead of value
• Calling Debug.Log without arguments
• Unnecessary string concatenation