Module 3: Decision Making in C++

Decision making allows a program to execute different blocks of code based on specific conditions. It helps create dynamic and interactive applications by evaluating whether a condition is true or false.

For example:

• Checking if a user is eligible to vote.
• Determining whether a student has passed or failed.
• Displaying different menu options based on user input.

1. if Statement

The if statement executes a block of code only if the specified condition is true.

Syntax

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1if (condition)
2{
3    // Code to execute if condition is true
4}

Example

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    int age = 20;
8
9    if (age >= 18)
10    {
11        cout << "Eligible to Vote";
12    }
13
14    return 0;
15}

Output

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1Eligible to Vote

2. if...else Statement

The if...else statement executes one block if the condition is true and another block if it is false.

Syntax

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1if (condition)
2{
3    // True block
4}
5else
6{
7    // False block
8}

Example

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    int marks = 45;
8
9    if (marks >= 50)
10    {
11        cout << "Pass";
12    }
13    else
14    {
15        cout << "Fail";
16    }
17
18    return 0;
19}

Output

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1Fail

3. Nested if

A nested if is an if statement inside another if statement. It is useful when multiple conditions need to be checked.

Syntax

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1if (condition1)
2{
3    if (condition2)
4    {
5        // Code
6    }
7}

Example

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    int age = 22;
8    bool hasLicense = true;
9
10    if (age >= 18)
11    {
12        if (hasLicense)
13        {
14            cout << "You can drive.";
15        }
16        else
17        {
18            cout << "License required.";
19        }
20    }
21    else
22    {
23        cout << "You are underage.";
24    }
25
26    return 0;
27}

Output

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1You can drive.

4. switch Statement

The switch statement selects one block of code from multiple options based on the value of an expression.

Syntax

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1switch (expression)
2{
3    case value1:
4        // Code
5        break;
6
7    case value2:
8        // Code
9        break;
10
11    default:
12        // Code
13}

Example

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    int day = 3;
8
9    switch (day)
10    {
11        case 1:
12            cout << "Monday";
13            break;
14
15        case 2:
16            cout << "Tuesday";
17            break;
18
19        case 3:
20            cout << "Wednesday";
21            break;
22
23        default:
24            cout << "Invalid Day";
25    }
26
27    return 0;
28}

Output

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1Wednesday

Note: The break statement prevents execution from continuing into the next case.

5. Conditional (Ternary) Operator

The conditional operator (?:) is a shorthand version of the if...else statement.

Syntax

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1condition ? expression1 : expression2;

Example

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1#include <iostream>
2
3using namespace std;
4
5int main()
6{
7    int age = 18;
8
9    string result = (age >= 18) ? "Adult" : "Minor";
10
11    cout << result;
12
13    return 0;
14}

Output

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1Adult

Comparison of Decision Statements

Best Practices

• Use meaningful conditions.
• Keep nested if statements to a minimum for better readability.
• Always include break in switch cases unless fall-through is intentional.
• Use the ternary operator only for simple conditions.
• Indent code properly to improve readability.

Common Mistakes

Using = Instead of ==

❌ Incorrect

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1if (age = 18)

✅ Correct

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1if (age == 18)

Forgetting break in switch

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1switch (choice)
2{
3    case 1:
4        cout << "Option 1";
5        break;
6
7    case 2:
8        cout << "Option 2";
9        break;
10}

Without break, execution continues into the next case.

Practice Exercises

1. Check whether a person is eligible to vote.
2. Find the larger of two numbers using if...else.
3. Check if a year is a leap year.
4. Create a simple calculator using switch.
5. Use the ternary operator to determine whether a number is even or odd.

Interview Questions

1. What is decision making in C++?
2. What is the difference between if and if...else?
3. When should you use a nested if?
4. What is the purpose of the switch statement?
5. Why is the break statement used in a switch?
6. What is the conditional (ternary) operator?
7. When is the ternary operator preferred over if...else?

Summary

In this module, you learned:

• How the if statement executes code based on a condition.
• How if...else provides two possible execution paths.
• How nested if statements evaluate multiple conditions.
• How the switch statement selects from multiple choices.
• How the conditional (ternary) operator offers a concise alternative to if...else.

In the next module, you'll learn Loops in C++, including for, while, do...while, range-based for loops, nested loops, and pattern printing.