Assignment operators in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add 5 to the variable num using an assignment operator.

Java

int num = 10;
num [1] 5;

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

A+=

B-=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' will subtract instead of add.

Using '*' or '/' will multiply or divide, not add.

The '+=' operator adds the right value to the variable and assigns the result back to it.

2fill in blank

medium

Complete the code to multiply value by 3 using an assignment operator.

Java

int value = 4;
value [1] 3;

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

A*=

B+=

C-=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' will add instead of multiply.

Using '-=' or '/=' will subtract or divide, not multiply.

The '*=' operator multiplies the variable by the right value and assigns the result back.

3fill in blank

hard

Fix the error in the code by choosing the correct assignment operator to subtract 2 from count.

Java

int count = 7;
count [1] 2;

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

A*=

B-=

C+=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' will increase instead of decrease.

Using '*=' or '/=' will multiply or divide, not subtract.

The '-=' operator subtracts the right value from the variable and assigns the result back.

4fill in blank

hard

Fill both blanks to divide total by 4 and assign the result back, then add 10 to total.

Java

int total = 40;
total [1] 4;
total [2] 10;

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

A/=

B+=

C-=

D*=

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up '+' and '-' operators.

Using '*=' instead of '/=' for division.

First, '/=' divides and assigns. Then, '+=' adds and assigns.

5fill in blank

hard

Fill all three blanks to multiply score by 2, subtract 5, then add 3.

Java

int score = 10;
score [1] 2;
score [2] 5;
score [3] 3;

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

A*=

B-=

C+=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+=' instead of '*=' for multiplication.

Mixing the order of operations.

Use '*=' to multiply, '-=' to subtract, and '+=' to add.

Practice

1. What does the assignment operator += do in Java?

easy

A. Divides the left variable by the right value

B. Subtracts the right value from the left variable

C. Multiplies the left variable by the right value

D. Adds the right value to the left variable and stores the result in the left variable

Solution

1. Step 1: Understand the += operator

   The += operator adds the right-hand side value to the left-hand side variable.

2. Step 2: Store the result back in the left variable

   The sum replaces the original value in the left variable.

3. Final Answer:

   Adds the right value to the left variable and stores the result in the left variable -> Option D

4. Quick Check:

   x += y means x = x + y [OK]

Hint: Think: add then assign back to the same variable [OK]

Common Mistakes:

• Confusing += with subtraction or multiplication
• Thinking it only adds without assignment
• Mixing up the order of operands

2. Which of the following is the correct syntax to multiply a variable num by 5 and assign the result back to num?

easy

A. num = * 5;

B. num *= 5;

C. num = num *;

D. num = 5 *;

Solution

1. Step 1: Identify the correct compound assignment syntax

   The operator *= multiplies and assigns in one step.

2. Step 2: Check the variable and value placement

   The correct form is num *= 5; which means num = num * 5;.

3. Final Answer:

   num *= 5; -> Option B

4. Quick Check:

   Use *= for multiply and assign [OK]

Hint: Look for operator before equals for combined action [OK]

Common Mistakes:

• Placing * after = without variable
• Leaving out the variable on right side
• Using invalid syntax like num = * 5

3. What is the output of this Java code?

int a = 10;
a -= 3;
a += 2;
System.out.println(a);

medium

A. 9

B. 11

C. 5

D. 15

Solution

1. Step 1: Calculate a -= 3;

   Subtract 3 from 10: 10 - 3 = 7, so a becomes 7.

2. Step 2: Calculate a += 2;

   Add 2 to 7: 7 + 2 = 9, so a becomes 9.

3. Step 3: Check the printed value

   The code prints the current value of a, which is 9.

4. Final Answer:

   9 -> Option A

5. Quick Check:

   10 - 3 + 2 = 9 [OK]

Hint: Perform each assignment step in order carefully [OK]

Common Mistakes:

• Adding before subtracting
• Mixing up += and -= effects
• Printing before assignment changes

4. Find the error in this code snippet:

int x = 5;
x + = 3;
System.out.println(x);

medium

A. Variable x is not initialized

B. Missing semicolon after System.out.println(x)

C. The operator + = has a space and is invalid

D. The code will print 8 without errors

Solution

1. Step 1: Check the operator syntax

   The operator += must not have spaces; + = is invalid.

2. Step 2: Confirm other syntax elements

   Variable x is initialized and semicolons are correct.

3. Final Answer:

   The operator + = has a space and is invalid -> Option C

4. Quick Check:

   No spaces allowed in compound assignment operators [OK]

Hint: Compound operators have no spaces, write as one token [OK]

Common Mistakes:

• Adding spaces inside operators
• Assuming code runs despite syntax errors
• Confusing initialization errors with operator errors

5. Given the code below, what is the final value of total?

int total = 20;
int discount = 5;
total -= discount *= 2;
System.out.println(total);

hard

A. 10

B. 30

C. 15

D. 5

Solution

1. Step 1: Evaluate discount *= 2;

   This multiplies discount by 2: 5 * 2 = 10, so discount becomes 10.

2. Step 2: Calculate total -= discount;

   Subtract discount (now 10) from total (20): 20 - 10 = 10.

3. Step 3: Confirm final value

   The final value of total is 10, which is printed.

4. Final Answer:

   10 -> Option A

5. Quick Check:

   discount = 5*2=10; total = 20-10=10 [OK]

Hint: Evaluate right side first in compound assignments [OK]

Common Mistakes:

• Ignoring that discount changes before subtraction
• Subtracting original discount value (5) instead of updated (10)
• Confusing order of operations in assignment