Why conditional logic is needed - See It in Action

Why conditional logic is needed

📖 Scenario: Imagine you are creating a simple program that decides if a person can enter a club based on their age. The club only allows people who are 18 years old or older.

🎯 Goal: You will build a small C program that uses conditional logic to check a person's age and print whether they can enter the club or not.

📋 What You'll Learn

Create an integer variable called age with the value 20

Create an integer variable called minimum_age with the value 18

Use an if statement to check if age is greater than or equal to minimum_age

Print "Access granted" if the condition is true

Print "Access denied" if the condition is false

💡 Why This Matters

🌍 Real World

Conditional logic is used in many real-world programs to make decisions, like checking user age for access, validating input, or controlling game rules.

💼 Career

Understanding conditional logic is essential for any programming job because it allows software to respond to different situations and user inputs.

1

Create the age variable

Create an integer variable called age and set it to 20.

C

#include 

int main() {
    // Create an integer variable called age and set it to 20
    // Your code here

    return 0;
}

Hint

Use int age = 20; inside the main function.

2

Create the minimum age variable

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

C

#include 

int main() {
    int age = 20;
    // Create an integer variable called minimum_age and set it to 18
    // Your code here

    return 0;
}

Hint

Use int minimum_age = 18; inside the main function.

3

Add conditional logic to check age

Use an if statement to check if age is greater than or equal to minimum_age. Inside the if, write printf("Access granted\n");. Use else to write printf("Access denied\n");.

C

#include 

int main() {
    int age = 20;
    int minimum_age = 18;
    // Use if to check if age >= minimum_age
    // Print "Access granted" if true
    // Use else to print "Access denied" if false
    // Your code here

    return 0;
}

Hint

Use if (age >= minimum_age) { ... } else { ... } to decide what to print.

4

Print the result

Run the program and print the output. The program should print Access granted because age is 20 and minimum_age is 18.

C

#include 

int main() {
    int age = 20;
    int minimum_age = 18;

    if (age >= minimum_age) {
        printf("Access granted\n");
    } else {
        printf("Access denied\n");
    }

    // Print the result
    // Your code here

    return 0;
}

Hint

Run the program to see the message printed.

Practice

1. Why do we use conditional logic like if statements in C programs?

easy

A. To repeat code multiple times

B. To make decisions based on different conditions

C. To store multiple values in one variable

D. To define new data types

Solution

1. Step 1: Understand the purpose of conditional logic

   Conditional logic allows a program to choose different actions depending on conditions.

2. Step 2: Compare with other options

   Repeating code is done with loops, storing values uses arrays or variables, and defining types uses structs or typedefs.

3. Final Answer:

   To make decisions based on different conditions -> Option B

4. Quick Check:

   Conditional logic = decision making [OK]

Hint: If you want choices, use if-else [OK]

Common Mistakes:

• Confusing loops with conditionals
• Thinking variables store multiple values
• Mixing data types with logic

2. Which of the following is the correct syntax for an if statement in C?

easy

A. if (condition) { /* code */ }

B. if condition { /* code */ }

C. if condition then { /* code */ }

D. if [condition] { /* code */ }

Solution

1. Step 1: Recall C syntax for if statements

   In C, conditions must be inside parentheses and code inside braces.

2. Step 2: Check each option

   if (condition) { /* code */ } matches the correct syntax: if (condition) { /* code */ }.

3. Final Answer:

   if (condition) { /* code */ } -> Option A

4. Quick Check:

   Parentheses around condition = correct syntax [OK]

Hint: Remember: if (condition) { } in C [OK]

Common Mistakes:

• Omitting parentheses around condition
• Using square brackets instead of parentheses
• Adding 'then' keyword which C does not use

3. What will be the output of this C code?

int x = 10;
if (x > 5) {
    printf("Big\n");
} else {
    printf("Small\n");
}

medium

A. Compilation error

B. Small

C. No output

D. Big

Solution

1. Step 1: Evaluate the condition

   The variable x is 10, which is greater than 5, so the condition (x > 5) is true.

2. Step 2: Determine which branch runs

   Since the condition is true, the code inside the if block runs, printing "Big".

3. Final Answer:

   Big -> Option D

4. Quick Check:

   10 > 5 is true, so prints Big [OK]

Hint: Check condition true or false to pick output [OK]

Common Mistakes:

• Confusing which block runs on true
• Ignoring the newline character
• Thinking else block runs when condition is true

4. Find the error in this C code snippet:

int num = 7;
if num > 5 {
    printf("Yes\n");
} else {
    printf("No\n");
}

medium

A. Missing parentheses around the condition

B. Missing semicolon after if statement

C. Incorrect use of else keyword

D. Variable num not declared

Solution

1. Step 1: Check the if statement syntax

   The condition in an if statement must be inside parentheses in C.

2. Step 2: Identify the error

   The code uses if num > 5 { ... } without parentheses, which is invalid syntax.

3. Final Answer:

   Missing parentheses around the condition -> Option A

4. Quick Check:

   If condition needs ( ) in C [OK]

Hint: Always put condition inside ( ) for if [OK]

Common Mistakes:

• Forgetting parentheses in if condition
• Adding semicolon after if line incorrectly
• Misplacing braces

5. You want to write a program that prints "Even" if a number is divisible by 2, and "Odd" otherwise. Which code snippet correctly uses conditional logic to do this?

hard

A. if (num % 2 != 0) {
printf("Even\n");
} else {
printf("Odd\n");
}

B. if (num / 2 == 0) {
printf("Even\n");
} else {
printf("Odd\n");
}

C. if (num % 2 == 0) {
printf("Even\n");
} else {
printf("Odd\n");
}

D. if (num % 2 = 0) {
printf("Even\n");
} else {
printf("Odd\n");
}

Solution

1. Step 1: Understand the condition for even numbers

   A number is even if dividing by 2 leaves remainder 0, checked by num % 2 == 0.

2. Step 2: Check each option's condition

   if (num % 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); } correctly uses num % 2 == 0. if (num / 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); } uses division instead of modulo. if (num % 2 = 0) { printf("Even\n"); } else { printf("Odd\n"); } uses assignment (=) instead of comparison (==). if (num % 2 != 0) { printf("Even\n"); } else { printf("Odd\n"); } reverses the logic.

3. Final Answer:

   if (num % 2 == 0) { printf("Even\n"); } else { printf("Odd\n"); } -> Option C

4. Quick Check:

   Modulo 2 equals 0 means even [OK]

Hint: Use modulo (%) to check divisibility [OK]

Common Mistakes:

• Using = instead of == in condition
• Using division instead of modulo
• Reversing if-else logic