Why conditional logic is needed

Introduction

Conditional logic helps a program make decisions. It lets the program choose what to do based on different situations.

When you want the program to do something only if a condition is true.

When you need to handle different actions for different user inputs.

When you want to check if a number is positive, negative, or zero and act accordingly.

When you want to repeat an action until a certain condition is met.

When you want to stop a program or show an error if something unexpected happens.

Syntax

C

if (condition) {
    // code to run if condition is true
} else {
    // code to run if condition is false
}

The condition is a test that results in true or false.

The else part is optional and runs when the condition is false.

Examples

This checks if someone is 18 or older to allow voting.

C

if (age >= 18) {
    printf("You can vote.\n");
} else {
    printf("You are too young to vote.\n");
}

This gives different messages based on the score.

C

if (score > 90) {
    printf("Excellent!\n");
} else if (score > 75) {
    printf("Good job!\n");
} else {
    printf("Keep trying!\n");
}

Sample Program

This program checks the temperature and prints a message based on whether it is hot or not.

C

#include <stdio.h>

int main() {
    int temperature = 30;

    if (temperature > 25) {
        printf("It's hot outside.\n");
    } else {
        printf("It's not too hot today.\n");
    }

    return 0;
}

Important Notes

Conditional logic is like asking a question and choosing what to do next based on the answer.

Without conditional logic, programs would do the same thing every time, no matter what.

Summary

Conditional logic lets programs make choices.

It helps handle different situations and inputs.

Using if and else is the basic way to add decision-making.

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