Control Flow in C++ - Complete Guide

Table of Contents

1. Introduction
2. Decision Making - if-else
3. Switch Case Statement
4. Loops
5. Break and Continue
6. Best Practices
7. Practice Problems

Introduction

Control flow statements allow your program to make decisions and repeat actions. Think of them as traffic signals and road signs that direct the flow of your program's execution.

Three main categories:

• Decision Making: if-else, switch (choosing a path)
• Loops: for, while, do-while (repeating actions)
• Jump Statements: break, continue (controlling loop behavior)

Decision Making - if-else

Basic if Statement

Executes code only if a condition is true.

Syntax:

if (condition) {
    // code to execute if condition is true
}

Example:

int age = 18;

if (age >= 18) {
    cout << "You are an adult." << endl;
}

if-else Statement

Provides an alternative when the condition is false.

Syntax:

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

Example:

int marks = 45;

if (marks >= 50) {
    cout << "You passed!" << endl;
} else {
    cout << "You failed. Try again!" << endl;
}

if-else if-else Ladder

Tests multiple conditions in sequence.

Syntax:

if (condition1) {
    // code if condition1 is true
} else if (condition2) {
    // code if condition2 is true
} else if (condition3) {
    // code if condition3 is true
} else {
    // code if all conditions are false
}

Example: Grade Calculator

#include <iostream>
using namespace std;

int main() {
    int marks;
    cout << "Enter your marks (0-100): ";
    cin >> marks;
    
    if (marks >= 90) {
        cout << "Grade: A+ (Excellent!)" << endl;
    } else if (marks >= 80) {
        cout << "Grade: A (Very Good)" << endl;
    } else if (marks >= 70) {
        cout << "Grade: B (Good)" << endl;
    } else if (marks >= 60) {
        cout << "Grade: C (Average)" << endl;
    } else if (marks >= 50) {
        cout << "Grade: D (Pass)" << endl;
    } else {
        cout << "Grade: F (Fail)" << endl;
    }
    
    return 0;
}

Nested if Statements

if statements inside other if statements.

Example: Login System

string username, password;
cout << "Enter username: ";
cin >> username;

if (username == "admin") {
    cout << "Enter password: ";
    cin >> password;
    
    if (password == "1234") {
        cout << "Login successful! Welcome, Admin." << endl;
    } else {
        cout << "Incorrect password!" << endl;
    }
} else {
    cout << "User not found!" << endl;
}

Ternary Operator (Shorthand if-else)

A compact way to write simple if-else statements.

Syntax:

condition ? value_if_true : value_if_false;

Example:

int age = 20;
string status = (age >= 18) ? "Adult" : "Minor";
cout << status << endl;  // Output: Adult

// Equivalent to:
string status;
if (age >= 18) {
    status = "Adult";
} else {
    status = "Minor";
}

More Examples:

int a = 10, b = 20;
int max = (a > b) ? a : b;  // max = 20

int marks = 75;
cout << "Result: " << (marks >= 50 ? "Pass" : "Fail") << endl;

Logical Operators in Conditions

Combine multiple conditions:

Basic Examples:

int age = 25;
bool hasLicense = true;

// AND operator
if (age >= 18 && hasLicense) {
    cout << "You can drive!" << endl;
}

// OR operator
string day = "Sunday";
if (day == "Saturday" || day == "Sunday") {
    cout << "It's the weekend!" << endl;
}

// NOT operator
bool isRaining = false;
if (!isRaining) {
    cout << "Let's go outside!" << endl;
}

// Complex condition
int marks = 85;
int attendance = 75;
if (marks >= 50 && attendance >= 75) {
    cout << "Eligible for certificate" << endl;
}

Short-Circuit Evaluation (IMPORTANT!)

C++ uses short-circuit evaluation for logical operators. This is a crucial concept for writing efficient and safe code.

How && (AND) Short-Circuits

Rule: If the first condition is FALSE, the remaining conditions are NOT evaluated.

Why? If one condition in AND is false, the entire expression is false. No need to check further.

Example 1: Basic Short-Circuit

int x = 5;
int y = 10;

// Second condition is NOT checked because first is false
if (x > 10 && y > 5) {
    cout << "This won't print" << endl;
}
// x > 10 is false, so y > 5 is never evaluated

Example 2: Demonstrating with Functions

#include <iostream>
using namespace std;

bool checkFirst() {
    cout << "Checking first condition..." << endl;
    return false;
}

bool checkSecond() {
    cout << "Checking second condition..." << endl;
    return true;
}

int main() {
    cout << "Testing AND (&&):" << endl;
    if (checkFirst() && checkSecond()) {
        cout << "Both true" << endl;
    }
    
    // Output:
    // Testing AND (&&):
    // Checking first condition...
    // (checkSecond() is NEVER called!)
    
    return 0;
}

Example 3: Preventing Division by Zero

int a = 10;
int b = 0;

// ✅ SAFE: b != 0 is checked first
if (b != 0 && a / b > 2) {
    cout << "Division result is greater than 2" << endl;
}
// If b is 0, the division never happens!

// ❌ DANGEROUS: Would crash if written the other way
// if (a / b > 2 && b != 0) {  // WRONG! Division happens first!

Example 4: Null Pointer Check

int* ptr = nullptr;

// ✅ SAFE: Check pointer before dereferencing
if (ptr != nullptr && *ptr > 10) {
    cout << "Value is greater than 10" << endl;
}
// If ptr is null, *ptr is never accessed

// ❌ DANGEROUS: Would crash
// if (*ptr > 10 && ptr != nullptr) {  // WRONG! Dereferencing null pointer!

How || (OR) Short-Circuits

Rule: If the first condition is TRUE, the remaining conditions are NOT evaluated.

Why? If one condition in OR is true, the entire expression is true. No need to check further.

Example 1: Basic Short-Circuit

int x = 15;
int y = 10;

// Second condition is NOT checked because first is true
if (x > 10 || y > 15) {
    cout << "At least one condition is true" << endl;
}
// x > 10 is true, so y > 15 is never evaluated

Example 2: Demonstrating with Functions

#include <iostream>
using namespace std;

bool checkFirst() {
    cout << "Checking first condition..." << endl;
    return true;
}

bool checkSecond() {
    cout << "Checking second condition..." << endl;
    return false;
}

int main() {
    cout << "Testing OR (||):" << endl;
    if (checkFirst() || checkSecond()) {
        cout << "At least one is true" << endl;
    }
    
    // Output:
    // Testing OR (||):
    // Checking first condition...
    // At least one is true
    // (checkSecond() is NEVER called!)
    
    return 0;
}

Example 3: Default Value Check

string username;
cout << "Enter username: ";
cin >> username;

// Check if empty first (fast check)
if (username.empty() || username == "guest") {
    username = "Anonymous";
}
// If username is empty, the comparison never happens

Example 4: Permission Check

bool isAdmin = false;
bool isOwner = true;
bool hasPermission = false;

// ✅ Efficient: Checks in order of likelihood
if (isAdmin || isOwner || hasPermission) {
    cout << "Access granted!" << endl;
}
// If isAdmin is true, other checks are skipped

Short-Circuit Evaluation Comparison

#include <iostream>
using namespace std;

int callCount = 0;

bool expensive_check() {
    callCount++;
    cout << "Expensive check called (count: " << callCount << ")" << endl;
    return true;
}

int main() {
    callCount = 0;
    
    // Test 1: AND with false first
    cout << "\n=== Test 1: AND with false first ===" << endl;
    if (false && expensive_check()) {
        cout << "This won't execute" << endl;
    }
    cout << "Expensive check was called " << callCount << " times" << endl;
    // Output: 0 times (never called!)
    
    // Test 2: AND with true first
    callCount = 0;
    cout << "\n=== Test 2: AND with true first ===" << endl;
    if (true && expensive_check()) {
        cout << "This will execute" << endl;
    }
    cout << "Expensive check was called " << callCount << " times" << endl;
    // Output: 1 time
    
    // Test 3: OR with true first
    callCount = 0;
    cout << "\n=== Test 3: OR with true first ===" << endl;
    if (true || expensive_check()) {
        cout << "This will execute" << endl;
    }
    cout << "Expensive check was called " << callCount << " times" << endl;
    // Output: 0 times (never called!)
    
    // Test 4: OR with false first
    callCount = 0;
    cout << "\n=== Test 4: OR with false first ===" << endl;
    if (false || expensive_check()) {
        cout << "This will execute" << endl;
    }
    cout << "Expensive check was called " << callCount << " times" << endl;
    // Output: 1 time
    
    return 0;
}

Best Practices for Logical Operators

1. Order Matters for Safety

Rule: Always put safety checks FIRST in AND operations.

// ✅ CORRECT: Check for null/zero first
if (ptr != nullptr && *ptr > 10) { }
if (denominator != 0 && numerator / denominator > 5) { }
if (!array.empty() && array[0] == 10) { }

// ❌ WRONG: Dangerous operations first
if (*ptr > 10 && ptr != nullptr) { }  // Crash if ptr is null!
if (numerator / denominator > 5 && denominator != 0) { }  // Division by zero!
if (array[0] == 10 && !array.empty()) { }  // Access invalid memory!

Real-World Example:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string* namePtr = nullptr;
    
    // ✅ SAFE: Check pointer first
    if (namePtr != nullptr && namePtr->length() > 0) {
        cout << "Name: " << *namePtr << endl;
    } else {
        cout << "No name available" << endl;
    }
    
    // ❌ This would CRASH:
    // if (namePtr->length() > 0 && namePtr != nullptr) { }
    
    return 0;
}

2. Order Matters for Performance

Rule: Put cheap/fast checks FIRST, expensive checks LAST.

int age = 25;
bool hasComplexPermission() {
    // Imagine this function does expensive database lookup
    // Takes 100ms to execute
    return true;
}

// ✅ EFFICIENT: Fast check first
if (age >= 18 && hasComplexPermission()) {
    cout << "Access granted" << endl;
}
// If age < 18, expensive function is never called

// ❌ INEFFICIENT: Expensive check first
if (hasComplexPermission() && age >= 18) {
    cout << "Access granted" << endl;
}
// Expensive function ALWAYS called, even if age < 18

Another Example:

string username = "john";
bool isDatabaseUserValid(string user) {
    // Expensive: queries database
    cout << "Querying database..." << endl;
    return true;
}

// ✅ EFFICIENT: Check local variable first
if (!username.empty() && username.length() > 3 && isDatabaseUserValid(username)) {
    cout << "Valid user" << endl;
}
// Database only queried if basic checks pass

// ❌ INEFFICIENT: Database check first
if (isDatabaseUserValid(username) && username.length() > 3) {
    cout << "Valid user" << endl;
}
// Database queried every time, even for invalid usernames

3. Order for OR Operations

Rule: Put most likely to be true conditions FIRST.

bool isWeekend(string day) {
    // ✅ EFFICIENT: Most common cases first
    if (day == "Saturday" || day == "Sunday") {
        return true;
    }
    return false;
}

// In a user role check:
bool hasAccess() {
    // Put most common role first
    // ✅ If 80% users are "member", check that first
    if (role == "member" || role == "admin" || role == "moderator") {
        return true;
    }
    return false;
}

4. Readability vs Performance Trade-off

Sometimes clarity is more important than micro-optimization:

// Option 1: Optimized but less clear
if (ptr && *ptr > 10 && calculate(ptr)) { }

// Option 2: Clearer with separate checks
if (ptr != nullptr) {
    if (*ptr > 10) {
        if (calculate(ptr)) {
            // do something
        }
    }
}

Best approach: Balance both:

// ✅ GOOD: Clear AND efficient
bool isValid = (ptr != nullptr);
bool hasValue = isValid && (*ptr > 10);
bool passesCalculation = hasValue && calculate(ptr);

if (passesCalculation) {
    // do something
}

5. Complex Conditions - Use Parentheses

// ❌ Confusing
if (a && b || c && d) { }

// ✅ Clear with parentheses
if ((a && b) || (c && d)) { }

// Even better with meaningful variables
bool firstConditionMet = (a && b);
bool secondConditionMet = (c && d);
if (firstConditionMet || secondConditionMet) { }

6. Avoid Side Effects in Conditions

int count = 0;

// ❌ BAD: Side effect (incrementing) in condition
if (count++ > 5 && someFunction()) {
    // count might not increment if first condition is false!
}

// ✅ GOOD: Separate side effects
count++;
if (count > 5 && someFunction()) {
    // Clear and predictable
}

Practical Scenarios

Scenario 1: Form Validation

#include <iostream>
#include <string>
using namespace std;

int main() {
    string email, password;
    
    cout << "Enter email: ";
    cin >> email;
    cout << "Enter password: ";
    cin >> password;
    
    // ✅ GOOD: Check simple conditions first
    if (!email.empty() && 
        email.find('@') != string::npos && 
        password.length() >= 8) {
        cout << "Registration successful!" << endl;
    } else {
        cout << "Invalid email or password too short" << endl;
    }
    
    return 0;
}

Scenario 2: Safe Array Access

#include <iostream>
using namespace std;

int main() {
    int scores[] = {85, 90, 78, 92, 88};
    int size = 5;
    int index;
    
    cout << "Enter index to view (0-4): ";
    cin >> index;
    
    // ✅ SAFE: Check bounds before accessing
    if (index >= 0 && index < size && scores[index] >= 80) {
        cout << "High score: " << scores[index] << endl;
    } else if (index >= 0 && index < size) {
        cout << "Score: " << scores[index] << endl;
    } else {
        cout << "Invalid index!" << endl;
    }
    
    return 0;
}

Scenario 3: User Permissions

#include <iostream>
#include <string>
using namespace std;

int main() {
    string role = "user";
    int accountAge = 30;  // days
    bool emailVerified = true;
    
    // ✅ Efficient: Check from least to most restrictive
    // Most users will fail early checks quickly
    if (emailVerified && 
        accountAge >= 7 && 
        (role == "admin" || role == "moderator" || role == "premium")) {
        cout << "Access to premium features granted!" << endl;
    } else {
        cout << "Upgrade to premium for this feature" << endl;
    }
    
    return 0;
}

Scenario 4: Game Damage Calculation

#include <iostream>
using namespace std;

int main() {
    int playerHealth = 50;
    int armor = 30;
    int incomingDamage = 40;
    bool hasShield = true;
    
    // ✅ Process shields first (cheaper check)
    if (hasShield && incomingDamage > 0) {
        cout << "Shield absorbed the damage!" << endl;
        hasShield = false;
    } else if (armor > 0 && incomingDamage > armor) {
        incomingDamage -= armor;
        armor = 0;
        playerHealth -= incomingDamage;
        cout << "Armor damaged! Health: " << playerHealth << endl;
    } else if (armor > 0) {
        armor -= incomingDamage;
        cout << "Armor absorbed damage. Remaining: " << armor << endl;
    } else {
        playerHealth -= incomingDamage;
        cout << "Direct hit! Health: " << playerHealth << endl;
    }
    
    if (playerHealth <= 0) {
        cout << "Game Over!" << endl;
    }
    
    return 0;
}

Summary: Logical Operators

Key Takeaways:

1. Safety first: Always check null/zero/bounds before using
2. Performance: Put cheap checks before expensive ones
3. Readability: Use parentheses for complex conditions
4. Predictability: Avoid side effects in conditions
5. Short-circuit is your friend: Use it to write safer, faster code

Switch Case Statement

Executes different code blocks based on the value of a variable. Better than multiple if-else when checking one variable against many values.

Basic Syntax

switch (expression) {
    case value1:
        // code for value1
        break;
    case value2:
        // code for value2
        break;
    case value3:
        // code for value3
        break;
    default:
        // code if no case matches
}

⚠️ Important:

• break is crucial - without it, execution "falls through" to next case
• switch works with int, char, and enum (NOT with string or float)
• default is optional but recommended

Example 1: Menu System

#include <iostream>
using namespace std;

int main() {
    int choice;
    cout << "=== Menu ===" << endl;
    cout << "1. Coffee" << endl;
    cout << "2. Tea" << endl;
    cout << "3. Juice" << endl;
    cout << "4. Water" << endl;
    cout << "Enter your choice (1-4): ";
    cin >> choice;
    
    switch (choice) {
        case 1:
            cout << "You ordered Coffee. Price: $3" << endl;
            break;
        case 2:
            cout << "You ordered Tea. Price: $2" << endl;
            break;
        case 3:
            cout << "You ordered Juice. Price: $4" << endl;
            break;
        case 4:
            cout << "You ordered Water. Price: Free!" << endl;
            break;
        default:
            cout << "Invalid choice!" << endl;
    }
    
    return 0;
}

Example 2: Day of the Week

char day;
cout << "Enter first letter of day (M/T/W/F/S): ";
cin >> day;

switch (day) {
    case 'M':
        cout << "Monday" << endl;
        break;
    case 'T':
        cout << "Tuesday or Thursday" << endl;
        break;
    case 'W':
        cout << "Wednesday" << endl;
        break;
    case 'F':
        cout << "Friday" << endl;
        break;
    case 'S':
        cout << "Saturday or Sunday" << endl;
        break;
    default:
        cout << "Invalid input!" << endl;
}

Fall-Through Cases (Intentional)

Sometimes you want multiple cases to execute the same code:

int month;
cout << "Enter month number (1-12): ";
cin >> month;

switch (month) {
    case 12:
    case 1:
    case 2:
        cout << "Winter" << endl;
        break;
    case 3:
    case 4:
    case 5:
        cout << "Spring" << endl;
        break;
    case 6:
    case 7:
    case 8:
        cout << "Summer" << endl;
        break;
    case 9:
    case 10:
    case 11:
        cout << "Fall" << endl;
        break;
    default:
        cout << "Invalid month!" << endl;
}

Calculator Example

double num1, num2;
char operation;

cout << "Enter first number: ";
cin >> num1;
cout << "Enter operation (+, -, *, /): ";
cin >> operation;
cout << "Enter second number: ";
cin >> num2;

switch (operation) {
    case '+':
        cout << "Result: " << (num1 + num2) << endl;
        break;
    case '-':
        cout << "Result: " << (num1 - num2) << endl;
        break;
    case '*':
        cout << "Result: " << (num1 * num2) << endl;
        break;
    case '/':
        if (num2 != 0) {
            cout << "Result: " << (num1 / num2) << endl;
        } else {
            cout << "Error: Division by zero!" << endl;
        }
        break;
    default:
        cout << "Invalid operation!" << endl;
}

↑ Back to Table of Contents

Loops

Loops allow you to execute code repeatedly. C++ has three types of loops.

1. for Loop

Best when you know how many times to repeat.

Syntax:

for (initialization; condition; update) {
    // code to repeat
}

Execution Flow:

1. Initialization: Runs once at the start
2. Condition: Checked before each iteration
3. Code Block: Executes if condition is true
4. Update: Runs after each iteration
5. Repeat steps 2-4 until condition is false

Example 1: Print 1 to 10

for (int i = 1; i <= 10; i++) {
    cout << i << " ";
}
// Output: 1 2 3 4 5 6 7 8 9 10

Example 2: Multiplication Table

int num;
cout << "Enter a number: ";
cin >> num;

cout << "Multiplication table of " << num << ":" << endl;
for (int i = 1; i <= 10; i++) {
    cout << num << " x " << i << " = " << (num * i) << endl;
}

Example 3: Sum of Numbers

int n, sum = 0;
cout << "Enter a number: ";
cin >> n;

for (int i = 1; i <= n; i++) {
    sum += i;  // sum = sum + i
}
cout << "Sum of first " << n << " numbers: " << sum << endl;

Example 4: Counting Down

for (int i = 10; i >= 1; i--) {
    cout << i << " ";
}
cout << "Blast off!" << endl;
// Output: 10 9 8 7 6 5 4 3 2 1 Blast off!

Example 5: Nested Loops (Pattern)

// Print a square pattern
for (int row = 1; row <= 5; row++) {
    for (int col = 1; col <= 5; col++) {
        cout << "* ";
    }
    cout << endl;
}
// Output:
// * * * * *
// * * * * *
// * * * * *
// * * * * *
// * * * * *

2. while Loop

Best when you don't know how many times to repeat (condition-based).

Syntax:

while (condition) {
    // code to repeat
}

Example 1: Basic Counter

int i = 1;
while (i <= 5) {
    cout << i << " ";
    i++;
}
// Output: 1 2 3 4 5

Example 2: User Input Validation

int password;
cout << "Enter password (1234): ";
cin >> password;

while (password != 1234) {
    cout << "Wrong password! Try again: ";
    cin >> password;
}
cout << "Access granted!" << endl;

Example 3: Menu System

int choice = 0;

while (choice != 4) {
    cout << "\n=== Menu ===" << endl;
    cout << "1. Start Game" << endl;
    cout << "2. Load Game" << endl;
    cout << "3. Settings" << endl;
    cout << "4. Exit" << endl;
    cout << "Choice: ";
    cin >> choice;
    
    switch (choice) {
        case 1:
            cout << "Starting game..." << endl;
            break;
        case 2:
            cout << "Loading game..." << endl;
            break;
        case 3:
            cout << "Opening settings..." << endl;
            break;
        case 4:
            cout << "Goodbye!" << endl;
            break;
        default:
            cout << "Invalid choice!" << endl;
    }
}

Example 4: Sum Until Negative

int num, sum = 0;

cout << "Enter numbers (negative to stop):" << endl;
cin >> num;

while (num >= 0) {
    sum += num;
    cin >> num;
}

cout << "Sum: " << sum << endl;

3. do-while Loop

Similar to while, but always executes at least once (checks condition at the end).

Syntax:

do {
    // code to repeat (runs at least once)
} while (condition);

Example 1: Basic Usage

int i = 1;
do {
    cout << i << " ";
    i++;
} while (i <= 5);
// Output: 1 2 3 4 5

Example 2: Menu (Guaranteed to Show Once)

char choice;

do {
    cout << "\n=== Options ===" << endl;
    cout << "A. Add" << endl;
    cout << "B. Delete" << endl;
    cout << "C. View" << endl;
    cout << "Q. Quit" << endl;
    cout << "Choice: ";
    cin >> choice;
    
    switch (choice) {
        case 'A':
        case 'a':
            cout << "Adding..." << endl;
            break;
        case 'B':
        case 'b':
            cout << "Deleting..." << endl;
            break;
        case 'C':
        case 'c':
            cout << "Viewing..." << endl;
            break;
        case 'Q':
        case 'q':
            cout << "Exiting..." << endl;
            break;
        default:
            cout << "Invalid choice!" << endl;
    }
} while (choice != 'Q' && choice != 'q');

Example 3: Input Validation

int age;

do {
    cout << "Enter your age (1-120): ";
    cin >> age;
    
    if (age < 1 || age > 120) {
        cout << "Invalid age! Please try again." << endl;
    }
} while (age < 1 || age > 120);

cout << "Age accepted: " << age << endl;

Loop Comparison

Choosing the Right Loop:

// for - when you know the count
for (int i = 0; i < 10; i++) { }

// while - checking condition first
while (userInput != "quit") { }

// do-while - must run at least once (like menus)
do {
    showMenu();
} while (choice != 0);

Break and Continue

Special statements that control loop execution.

break Statement

Purpose: Immediately exits the loop completely.

Example 1: Exit on Condition

for (int i = 1; i <= 10; i++) {
    if (i == 6) {
        break;  // Stop loop when i equals 6
    }
    cout << i << " ";
}
// Output: 1 2 3 4 5

Example 2: Search in Loop

int numbers[] = {10, 20, 30, 40, 50};
int target = 30;
bool found = false;

for (int i = 0; i < 5; i++) {
    if (numbers[i] == target) {
        cout << "Found " << target << " at index " << i << endl;
        found = true;
        break;  // No need to continue searching
    }
}

if (!found) {
    cout << target << " not found!" << endl;
}

Example 3: Exit on User Command

while (true) {  // Infinite loop
    string command;
    cout << "Enter command (type 'exit' to quit): ";
    cin >> command;
    
    if (command == "exit") {
        cout << "Goodbye!" << endl;
        break;  // Exit the infinite loop
    }
    
    cout << "You entered: " << command << endl;
}

Example 4: break in switch (already seen)

switch (choice) {
    case 1:
        cout << "Option 1" << endl;
        break;  // Prevents fall-through
    case 2:
        cout << "Option 2" << endl;
        break;
}

continue Statement

Purpose: Skips the rest of current iteration and moves to the next iteration.

Example 1: Skip Specific Values

for (int i = 1; i <= 10; i++) {
    if (i == 5) {
        continue;  // Skip when i is 5
    }
    cout << i << " ";
}
// Output: 1 2 3 4 6 7 8 9 10 (5 is skipped)

Example 2: Print Only Odd Numbers

for (int i = 1; i <= 10; i++) {
    if (i % 2 == 0) {
        continue;  // Skip even numbers
    }
    cout << i << " ";
}
// Output: 1 3 5 7 9

Example 3: Skip Negative Numbers

int numbers[] = {5, -2, 8, -1, 10, -3, 7};

cout << "Positive numbers: ";
for (int i = 0; i < 7; i++) {
    if (numbers[i] < 0) {
        continue;  // Skip negative numbers
    }
    cout << numbers[i] << " ";
}
// Output: Positive numbers: 5 8 10 7

Example 4: Input Validation

int sum = 0;
for (int i = 0; i < 5; i++) {
    int num;
    cout << "Enter number " << (i+1) << ": ";
    cin >> num;
    
    if (num < 0) {
        cout << "Negative numbers not allowed. Skipping..." << endl;
        continue;  // Skip this iteration
    }
    
    sum += num;
}
cout << "Sum of valid numbers: " << sum << endl;

break vs continue Comparison

// Example demonstrating both

cout << "Using break:" << endl;
for (int i = 1; i <= 10; i++) {
    if (i == 6) {
        break;  // Exit loop completely
    }
    cout << i << " ";
}
// Output: 1 2 3 4 5

cout << "\n\nUsing continue:" << endl;
for (int i = 1; i <= 10; i++) {
    if (i == 6) {
        continue;  // Skip only 6
    }
    cout << i << " ";
}
// Output: 1 2 3 4 5 7 8 9 10

Visual Difference:

Nested Loop Control

// break only exits the innermost loop
for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        if (j == 2) {
            break;  // Only exits inner loop
        }
        cout << i << "," << j << " ";
    }
    cout << endl;
}
// Output:
// 1,1
// 2,1
// 3,1

// continue only affects current loop
for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        if (j == 2) {
            continue;  // Skip j=2 in inner loop
        }
        cout << i << "," << j << " ";
    }
    cout << endl;
}
// Output:
// 1,1 1,3
// 2,1 2,3
// 3,1 3,3

Best Practices

1. Choosing the Right Control Structure

// ✅ Use switch for multiple discrete values
switch (menuChoice) {
    case 1: /* ... */ break;
    case 2: /* ... */ break;
}

// ✅ Use if-else for ranges or complex conditions
if (score >= 90) {
    // ...
} else if (score >= 80) {
    // ...
}

// ✅ Use for loop when iteration count is known
for (int i = 0; i < 10; i++) { }

// ✅ Use while when condition-based
while (userInput != "quit") { }

// ✅ Use do-while for at-least-once execution
do {
    showMenu();
} while (choice != 0);

2. Always Use Braces

// ❌ Dangerous (easy to make mistakes)
if (condition)
    doSomething();

// ✅ Safe and clear
if (condition) {
    doSomething();
}

3. Avoid Deep Nesting

// ❌ Hard to read
if (condition1) {
    if (condition2) {
        if (condition3) {
            // deeply nested code
        }
    }
}

// ✅ Better - early returns
if (!condition1) return;
if (!condition2) return;
if (!condition3) return;
// main code here

4. Initialize Loop Variables

// ✅ Always initialize
for (int i = 0; i < 10; i++) { }

// ❌ Uninitialized variable
int i;
for (i; i < 10; i++) { }  // i has garbage value initially

5. Avoid Infinite Loops (Unless Intentional)

// ❌ Accidental infinite loop
for (int i = 0; i < 10; i--) {  // i decreases!
    // never ends
}

// ✅ Intentional infinite loop with break
while (true) {
    if (exitCondition) {
        break;
    }
}

6. Use Meaningful Variable Names

// ❌ Unclear
for (int i = 0; i < n; i++) { }

// ✅ Clear
for (int studentIndex = 0; studentIndex < totalStudents; studentIndex++) { }

// ✅ Or use range-based for loop
for (auto student : students) { }

7. Avoid Magic Numbers

// ❌ What does 7 mean?
for (int i = 0; i < 7; i++) { }

// ✅ Use constants
const int DAYS_IN_WEEK = 7;
for (int day = 0; day < DAYS_IN_WEEK; day++) { }

8. break and continue Guidelines

// ✅ Use break to exit when found
for (int i = 0; i < size; i++) {
    if (array[i] == target) {
        found = true;
        break;  // No need to continue searching
    }
}

// ✅ Use continue to skip invalid data
for (int i = 0; i < size; i++) {
    if (data[i] < 0) {
        continue;  // Skip negative values
    }
    processData(data[i]);
}

Practice Problems

Test your understanding with these exercises:

Problem 1: Even or Odd Checker

Write a program that asks for a number and tells if it's even or odd.

Problem 2: Simple Calculator

Create a calculator using switch-case that performs +, -, *, / operations.

Problem 3: Factorial Calculator

Calculate factorial of a number using a loop. (5! = 5 × 4 × 3 × 2 × 1 = 120)

Problem 4: Prime Number Checker

Check if a number is prime (only divisible by 1 and itself).

Problem 5: Pattern Printing

Print the following pattern:

*
**
***
****
*****

Problem 6: Number Guessing Game

Create a game where the computer picks a random number (1-100) and the user guesses. Use loops and break/continue appropriately.

Summary

Decision Making:

• Use if-else for conditions and ranges
• Use switch-case for multiple discrete values
• Use ternary operator ? : for simple conditions

Loops:

• for: When you know iteration count
• while: Condition checked first
• do-while: Runs at least once

Control Statements:

• break: Exit loop completely
• continue: Skip current iteration

Key Takeaways:

• Always use braces {} for clarity
• Initialize variables before loops
• Avoid infinite loops (unless intentional)
• Use meaningful variable names
• Comment complex logic
• Choose the right control structure for the task

With these fundamentals, you can now control the flow of any C++ program! 🚀