Assignment operators in C - Mini Project: Build & Apply

Using Assignment Operators in C

📖 Scenario: You are managing a small store's inventory. You want to update the stock counts efficiently using assignment operators.

🎯 Goal: Learn how to use assignment operators like =, +=, -=, *=, and /= to update variables in C.

📋 What You'll Learn

Create integer variables with exact initial values

Use assignment operators to update these variables

Print the final values to see the changes

💡 Why This Matters

🌍 Real World

Stores and businesses often update inventory counts quickly using assignment operators in their software.

💼 Career

Understanding assignment operators is essential for writing efficient and readable code in many programming jobs.

1

Create initial stock variables

Create three integer variables called apples, oranges, and bananas with values 50, 30, and 20 respectively.

C

# Create integer variables apples, oranges, and bananas with values 50, 30, and 20
// Your code here

Hint

Use the syntax int variable_name = value; to create variables.

2

Add new stock using += operator

Add 10 to apples and 5 to oranges using the += assignment operator.

C

int apples = 50;
int oranges = 30;
int bananas = 20;

// Add 10 to apples and 5 to oranges using +=
// Your code here

Hint

The += operator adds a value to the variable and updates it.

3

Remove some bananas using -= operator

Subtract 7 from bananas using the -= assignment operator.

C

int apples = 50;
int oranges = 30;
int bananas = 20;
apples += 10;
oranges += 5;

// Subtract 7 from bananas using -=
// Your code here

Hint

The -= operator subtracts a value from the variable and updates it.

4

Print the final stock counts

Use printf to print the values of apples, oranges, and bananas each on a new line with the exact format:
Apples: 60
Oranges: 35
Bananas: 13

C

int apples = 50;
int oranges = 30;
int bananas = 20;
apples += 10;
oranges += 5;
bananas -= 7;

// Print the final values of apples, oranges, and bananas
// Your code here

Hint

Use printf("Label: %d\n", variable); to print each variable with its label.

Practice

1. Which of the following assignment operators adds the right operand to the left operand and then assigns the result to the left operand?

easy

A. -=

B. +=

C. *=

D. /=

Solution

1. Step 1: Understand the meaning of += operator

   The operator += adds the value on the right to the variable on the left and stores the result back in the left variable.

2. Step 2: Compare with other operators

   Other operators like -= subtract, *= multiply, and /= divide, so they do not add.

3. Final Answer:

   += -> Option B

4. Quick Check:

   += means add and assign [OK]

Hint: Remember '+=' means add then assign to left variable [OK]

Common Mistakes:

• Confusing '+=' with '=' which just assigns
• Mixing '+=' with '-=' or '*='
• Thinking '+=' only adds without assignment

2. Which of the following is the correct syntax using the compound assignment operator to multiply variable x by 5 and assign the result back to x?

easy

A. x = x *5;

B. x =* 5;

C. x = *5;

D. x *= 5;

Solution

1. Step 1: Identify correct compound assignment syntax

   The correct syntax for multiplying and assigning is 'x *= 5;'. It combines multiplication and assignment.

2. Step 2: Check other options for syntax errors

   x =* 5; 'x =* 5;' is invalid syntax. x = *5; 'x = *5;' is invalid because '*5' is not a valid expression. x = x *5; 'x = x *5;' is correct but not a compound assignment operator.

3. Final Answer:

   x *= 5; -> Option D

4. Quick Check:

   '*=' is multiply and assign operator [OK]

Hint: Use '*=' to multiply and assign in one step [OK]

Common Mistakes:

• Writing '=*' instead of '*='
• Forgetting space or semicolon
• Using 'x = *5;' which is invalid

3. What is the output of the following code?

int a = 10;
a += 5;
a -= 3;
printf("%d", a);

medium

A. 8

B. 15

C. 12

D. 10

Solution

1. Step 1: Calculate after first operation 'a += 5;'

   Starting with a = 10, adding 5 gives a = 15.

2. Step 2: Calculate after second operation 'a -= 3;'

   Subtracting 3 from 15 gives a = 12.

3. Final Answer:

   12 -> Option C

4. Quick Check:

   10 + 5 - 3 = 12 [OK]

Hint: Apply each operator step-by-step to track value [OK]

Common Mistakes:

• Adding and subtracting in wrong order
• Confusing '+=' and '-=' effects
• Ignoring initial value of variable

4. Identify the error in the following code snippet:

int x = 7;
x +== 3;
printf("%d", x);

medium

A. Syntax error due to '+==' operator

B. Runtime error due to invalid operation

C. No error, output is 10

D. Logical error, output is wrong

Solution

1. Step 1: Check the operator '+==' in the code

   The operator '+==' does not exist in C. The correct operator for addition assignment is '+='.

2. Step 2: Understand the effect of invalid operator

   Using '+==' causes a syntax error and the code will not compile.

3. Final Answer:

   Syntax error due to '+==' operator -> Option A

4. Quick Check:

   Invalid operator '+==' causes syntax error [OK]

Hint: Use '+=' not '+==' for addition assignment [OK]

Common Mistakes:

• Typing '+==' instead of '+='
• Assuming '+==' works like '=='
• Ignoring compiler error messages

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

int result = 20;
result /= 4;
result *= 3;
result %= 5;
result += 2;
printf("%d", result);

hard

A. 2

B. 3

C. 4

D. 1

Solution

1. Step 1: Perform division assignment 'result /= 4;'

   Starting with result = 20, dividing by 4 gives result = 5.

2. Step 2: Perform multiplication assignment 'result *= 3;'

   Multiplying 5 by 3 gives result = 15.

3. Step 3: Perform modulus assignment 'result %= 5;'

   15 modulo 5 is 0, so result = 0.

4. Step 4: Perform addition assignment 'result += 2;'

   Adding 2 to 0 gives result = 2.

5. Final Answer:

   2 -> Option A

6. Quick Check:

   20/4=5, 5*3=15, 15%5=0, 0+2=2 [OK]

Hint: Apply each operator in order carefully [OK]

Common Mistakes:

• Skipping modulus step or calculating it wrong
• Mixing up order of operations
• Forgetting that %= gives remainder