Logical operators - Mini Project: Build & Apply

Logical Operators in C

📖 Scenario: You are creating a simple program to check if a person is eligible for a special discount based on their age and membership status.

🎯 Goal: Build a C program that uses logical operators to decide if a person qualifies for the discount.

📋 What You'll Learn

Create variables with exact names and values as instructed

Use the logical AND && operator

Print the exact output as specified

💡 Why This Matters

🌍 Real World

Logical operators are used in programs to make decisions, like checking if someone qualifies for discounts or access.

💼 Career

Understanding logical operators is essential for writing conditions in software development, quality assurance, and data validation.

1

Create variables for age and membership status

Create an integer variable called age and set it to 25. Create an integer variable called is_member and set it to 1 (1 means true, 0 means false).

C

# Create an integer variable called age and set it to 25
# Create an integer variable called is_member and set it to 1

Hint

Use int to declare variables and assign the values exactly as given.

2

Create a variable for minimum age

Create an integer variable called min_age and set it to 18.

C

int age = 25;
int is_member = 1;
# Create an integer variable called min_age and set it to 18

Hint

This variable will be used to check if the person is old enough for the discount.

3

Use logical operators to check eligibility

Create an integer variable called eligible and set it to the result of the expression: (age >= min_age) && (is_member == 1).

C

int age = 25;
int is_member = 1;
int min_age = 18;
# Create an integer variable called eligible and set it to (age >= min_age) && (is_member == 1)

Hint

Use the logical AND operator && to combine the two conditions.

4

Print the eligibility result

Write a printf statement to print "Eligible: 1" if the person is eligible, or "Eligible: 0" if not, by printing the value of eligible.

C

int age = 25;
int is_member = 1;
int min_age = 18;
int eligible = (age >= min_age) && (is_member == 1);
# Print the eligibility result using printf

Hint

Use printf("Eligible: %d\n", eligible); to print the result.

Practice

1. Which logical operator in C means AND and returns true only if both conditions are true?

easy

A. !

B. ||

C. &&

D. &

Solution

1. Step 1: Understand logical AND operator

   The logical AND operator (&&) returns true only if both conditions it connects are true.

2. Step 2: Compare with other operators

   The || operator means OR, ! means NOT, and & is bitwise AND, not logical AND.

3. Final Answer:

   && -> Option C

4. Quick Check:

   AND = && [OK]

Hint: AND operator is double ampersand && [OK]

Common Mistakes:

• Confusing & (bitwise) with && (logical)
• Mixing OR and AND operators
• Using ! for AND

2. Which of the following is the correct syntax to negate a condition in C?

easy

A. condition !

B. !condition

C. not condition

D. condition != true

Solution

1. Step 1: Identify negation syntax in C

   The NOT operator in C is a single exclamation mark placed before the condition: !condition.

2. Step 2: Check other options

   condition ! places ! after condition which is invalid, C uses 'not' which is not C syntax, D is a comparison, not negation.

3. Final Answer:

   !condition -> Option B

4. Quick Check:

   NOT = ! before condition [OK]

Hint: Negate condition with ! before it [OK]

Common Mistakes:

• Putting ! after condition
• Using 'not' keyword
• Confusing != with negation

3. What is the output of this C code?

int a = 5, b = 10;
if (a > 3 && b < 15) {
    printf("True\n");
} else {
    printf("False\n");
}

medium

A. No output

B. False

C. Compilation error

D. True

Solution

1. Step 1: Evaluate first condition (a > 3)

   a is 5, which is greater than 3, so this condition is true.

2. Step 2: Evaluate second condition (b < 15)

   b is 10, which is less than 15, so this condition is true.

3. Step 3: Apply logical AND (&&)

   Both conditions are true, so the combined condition is true, entering the if block.

4. Final Answer:

   True -> Option D

5. Quick Check:

   True && True = True [OK]

Hint: Both conditions true means && condition is true [OK]

Common Mistakes:

• Assuming OR instead of AND
• Misreading variable values
• Ignoring logical operator precedence

4. Find the error in this C code snippet:

int x = 0;
if (x = 5 || x == 0) {
    printf("Yes\n");
}

medium

A. Using assignment '=' instead of comparison '==' in if condition

B. Missing semicolon after printf statement

C. Incorrect use of logical AND instead of OR

D. Variable x is not declared

Solution

1. Step 1: Check the if condition syntax

   The condition uses 'x = 5 || x == 0'. The '=' is assignment, not comparison.

2. Step 2: Understand effect of assignment in condition

   Assignment returns the assigned value (5), which is true, so condition always true, likely a bug.

3. Final Answer:

   Using assignment '=' instead of comparison '==' in if condition -> Option A

4. Quick Check:

   Use '==' for comparison, not '=' [OK]

Hint: Use '==' to compare, '=' assigns value [OK]

Common Mistakes:

• Confusing '=' and '=='
• Ignoring logical operator precedence
• Assuming code won't compile

5. Given the code below, what will be printed?

int a = 0, b = 1, c = 2;
if (!(a || b) && c > 1) {
    printf("Inside if\n");
} else {
    printf("Inside else\n");
}

hard

A. Inside else

B. Inside if

C. Compilation error

D. No output

Solution

1. Step 1: Evaluate inner OR condition (a || b)

   a is 0 (false), b is 1 (true), so a || b is true.

2. Step 2: Apply NOT operator !(a || b)

   NOT true is false, so this part is false.

3. Step 3: Evaluate c > 1

   c is 2, which is greater than 1, so true.

4. Step 4: Combine with AND: false && true

   False AND anything is false, so condition is false, else block runs.

5. Final Answer:

   Inside else -> Option A

6. Quick Check:

   !(true) && true = false [OK]

Hint: NOT true is false; AND with false is false [OK]

Common Mistakes:

• Ignoring NOT operator effect
• Misreading OR condition
• Assuming if block runs when condition false