Condition Statements

C++ Conditional Statements: if, if...else, and Nested if...else

C++ provides several ways to implement decision-making in programs through conditional statements. The most common are the if, if...else, and nested if...else statements. Below, we will explore the syntax and provide examples for each type.

if Statement

The simplest form of decision-making is the if statement, which executes a block of code if a specified condition evaluates to true.

Syntax:

if (condition) {

// Code to execute if condition is true

}

Example:

#include <iostream>

using namespace std;

int main() {

int x = 18;

if (x % 2 == 0) {

cout << "The number is even." << endl;

}

return 0;

}

Output:

The number is even.

In this example, since 18 mod 2=0, the condition is true, and the message is printed.

if...else Statement

The if...else statement allows for two paths of execution: one for when the condition is true and another for when it is false.

Syntax:

if (condition) {

// Code to execute if condition is true

} else {

// Code to execute if condition is false

}

Example:

#include <iostream>

using namespace std;

int main() {

int age = 17;

if (age > 18) {

cout << "The person is an adult." << endl;

} else {

cout << "The person is not an adult." << endl;

}

return 0;

}

Output:

The person is not an adult.

Here, since the age is less than 18, the else block executes.

Nested if...else Statements

Nested if...else statements allow you to place one or more if statements inside another if or else block. This structure increases flexibility but can also complicate the code.

Syntax:

if (condition1) {

// Outer if block

if (condition2) {

// Inner if block

} else {

// Inner else block

}

} else {

// Outer else block

}

Example:

#include <iostream>

using namespace std;

int main() {

int age = 16;

if (age > 14) {

if (age >= 18) {

cout << "Adult" << endl;

} else {

cout << "Teenager" << endl;

}

} else {

cout << "Child" << endl;

}

return 0;

}

Output:

Teenager

In this case, since the age is greater than 14 but less than 18, the inner else block executes, indicating that the person is a teenager.

Summary

if Statement: Executes a block of code based on a true condition.
if...else Statement: Provides two paths of execution based on whether a condition is true or false.
Nested if...else: Allows for more complex decision-making by placing additional conditions inside existing ones.

C++ Ternary Operator

The ternary operator in C++ is a concise way to evaluate a condition and return one of two values based on whether the condition is true or false. It is also known as the conditional operator and is represented by the symbols ? :.

Syntax

The syntax for the ternary operator is as follows:

condition ? expression1 : expression2;

condition: This is the expression that gets evaluated.
expression1: This expression is executed if the condition evaluates to true.
expression2: This expression is executed if the condition evaluates to false.

Example of Ternary Operator

Here's a simple example that demonstrates how to use the ternary operator:

#include <iostream>

using namespace std;

int main() {

double marks;

cout << "Enter your marks: ";

cin >> marks;

// Using the ternary operator

string result = (marks >= 40) ? "passed" : "failed";

cout << "You " << result << " the exam." << endl;

return 0;

}

In this example:

If the user enters 80, the output will be:

You passed the exam.

If the user enters 39.5, the output will be:

You failed the exam.

Comparison with if...else

The ternary operator can often replace simple if...else statements, making code more concise. For instance, consider this equivalent code using if...else:

#include <iostream>

using namespace std;

int main() {

int age = 20;

string status;

// Using if...else

if (age >= 18) {

status = "Adult";

} else {

status = "Minor";

}

cout << "Status: " << status << endl;

return 0;

}

This can be simplified using the ternary operator:

#include <iostream>

using namespace std;

int main() {

int age = 20;

// Using ternary operator

string status = (age >= 18) ? "Adult" : "Minor";

cout << "Status: " << status << endl;

return 0;

}

Nested Ternary Operators

You can also nest ternary operators, although this can make your code harder to read. Here’s an example that determines whether a number is positive, negative, or zero:

#include <iostream>

using namespace std;

int main() {

int number = 0;

// Nested ternary operator

string result = (number > 0) ? "Positive" : (number < 0 ? "Negative" : "Zero");

cout << "Number is " << result << endl;

return 0;

}

In this case, if number is 0, it will output:

Number is Zero

Conclusion

The ternary operator in C++ provides a compact syntax for conditional expressions and can enhance code readability for simple conditions. However, it’s advisable to use it judiciously; for more complex conditions, traditional if...else statements may be preferable to maintain clarity.

Switch Case

The switch statement in C++ is a control flow statement that allows the execution of different blocks of code based on the value of a single variable or expression. It provides an alternative to using multiple if...else statements, especially when dealing with multiple discrete values.

Syntax

The basic syntax of a switch statement is as follows:

switch (expression) {

case constant1:

// Code to execute if expression equals constant1

break; // Optional

case constant2:

// Code to execute if expression equals constant2

break; // Optional

// You can have any number of case statements

default:

// Code to execute if none of the cases match

}

Key Components

Expression: The variable or expression evaluated once. It must be of an integral type (like int or char).
Case Labels: Each case label must be a constant expression that matches the type of the switch expression.
Break Statement: The break statement exits the switch block. Without it, execution will continue ("fall through") to subsequent cases.
Default Case: The default case is optional and executes if none of the specified cases match.

Example

Here’s a simple example demonstrating the use of a switch statement:

#include <iostream>

using namespace std;

int main() {

int num;

cout << "Enter a number (1-3): ";

cin >> num;

switch (num) {

case 1:

cout << "You entered One." << endl;

break;

case 2:

cout << "You entered Two." << endl;

break;

case 3:

cout << "You entered Three." << endl;

break;

default:

cout << "Invalid input!" << endl;

}

return 0;

}

Output:

Enter a number (1-3): 2

You entered Two.

Nested Switch Statements

You can also nest switch statements within one another. Here’s an example:

#include <iostream>

using namespace std;

int main() {

int i = 10, j = 20;

switch (i) {

case 10:

cout << "i is 10" << endl;

switch (j) {

case 20:

cout << "j is 20" << endl;

break;

default:

cout << "j is not 20" << endl;

}

break;

default:

cout << "i is not 10" << endl;

}

return 0;

}

Output:

i is 10

j is 20

Advantages of Using Switch Statements

Readability: Switch statements can be easier to read than long chains of if...else statements.
Performance: They can be optimized by compilers for faster execution compared to multiple if...else checks.
Structured Logic: They help organize code better when handling multiple discrete values.

Conclusion

The switch statement in C++ is a powerful tool for control flow, especially when dealing with multiple potential values for a single variable. It enhances code clarity and can improve performance in certain scenarios.

Loops

C++ provides several types of loops that allow programmers to execute a block of code multiple times. The main types of loops in C++ are for loops, while loops, and do-while loops. Each type serves different use cases depending on the requirements of the program.

For Loop

The for loop is particularly useful when the number of iterations is known beforehand. Its syntax is as follows:

for (initialization; condition; update) {

// body of loop

}

Initialization: This part is executed once at the beginning and is typically used to initialize a counter variable.
Condition: Before each iteration, this condition is evaluated. If true, the loop body executes; if false, the loop terminates.
Update: This statement updates the counter variable after each iteration.

Example

Here’s a simple example that prints numbers from 0 to 4:

#include <iostream>

using namespace std;

int main() {

for (int i = 0; i < 5; i++) {

cout << i << "\n";

}

return 0;

}

In this example:

The initialization sets i to 0.
The condition checks if i is less than 5.
The update increments i by 1 after each iteration.

Nested For Loop

C++ also allows for nested loops, where one for loop is placed inside another. This can be useful for tasks that require multiple levels of iteration.

for (int i = 1; i <= 3; i++) {

for (int j = 1; j <= 2; j++) {

cout << "i: " << i << ", j: " << j << "\n";

}

This will produce:

i: 1, j: 1

i: 1, j: 2

i: 2, j: 1

i: 2, j: 2

i: 3, j: 1

i: 3, j: 2

While Loop

The while loop continues to execute as long as a specified condition remains true. Its syntax is:

while (condition) {

// body of loop

}

Example

#include <iostream>

using namespace std;

int main() {

int i = 0;

while (i < 5) {

cout << i << "\n";

i++;

}

return 0;

}

This loop will produce the same output as the previous for loop example.

Do-While Loop

The do-while loop is similar to the while loop but guarantees that the body of the loop executes at least once before checking the condition. Its syntax is:

do {

// body of loop

} while (condition);

Example

#include <iostream>

using namespace std;

int main() {

int i = 0;

do {

cout << i << "\n";

i++;

} while (i < 5);

return 0;

}

This will also print numbers from 0 to 4, ensuring that even if the condition were false initially, the loop would execute at least once.

Range-Based For Loop

Introduced in C++11, the range-based for loop simplifies iterating over collections such as arrays and vectors. Its syntax is:

for (variable : collection) {

// body of loop

}

Example

#include <iostream>

using namespace std;

int main() {

int num_array[] = {1, 2, 3, 4, 5};

for (int n : num_array) {

cout << n << " ";

}

return 0;

}

This will output:

1 2 3 4 5

Conclusion

Loops are fundamental constructs in C++ that enable efficient code execution by allowing repeated execution of code blocks under specified conditions. Understanding when and how to use each type of loop can significantly enhance programming efficiency and clarity.