Introduction to Variables

In C++, variables are used to store and manipulate data. They allow us to assign values to a memory location and perform operations on those values. Variables can hold different types of data, such as numbers, characters, and strings.

To declare a variable in C++, we specify the data type followed by the variable name. For example, to declare an integer variable named age, we would write:

1int age;

This creates a variable named age of type int, which can store whole numbers. We can then assign a value to age using the assignment operator =:

1age = 25;

We can also initialize a variable at the time of declaration by providing an initial value:

1int height = 180;

Once a variable is declared and assigned a value, we can use it in expressions. For example:

1int width = 10;
2int area = width * height;

In this example, we multiply the value of width by the value of height and store the result in the variable area.

C++ also provides different data types for other kinds of values, such as floating-point numbers, characters, and boolean values. We can declare variables of these types using the appropriate keywords:

1float pi = 3.14;
2char grade = 'A';
3bool isPassed = true;

Using variables in C++ allows us to write dynamic and reusable code. We can store and manipulate values as needed, making our programs more flexible and adaptable.

In the next lesson, we will explore the different data types in C++ and learn how to use them effectively.

Data Types in C++

In C++, data types are used to specify the type and size of data that can be stored in variables. Each data type has a different set of values it can represent and occupies a specific amount of memory.

Here are some of the commonly used data types in C++:

• int: Used to store whole numbers (e.g., 10, -5, 1000).
• float: Used to store floating-point numbers with a decimal part (e.g., 3.14, -0.5, 2.0).
• char: Used to store single characters (e.g., 'a', 'X', '@').
• bool: Used to store boolean values (either true or false).

These data types can be used to declare variables and assign values to them. Here's an example:

1#include <iostream>
2using namespace std;
3
4int main() {
5  int age = 30;
6  float height = 180.5;
7  char grade = 'A';
8  bool isProgrammer = true;
9
10  // Output the values
11  cout << "My age is " << age << endl;
12  cout << "My height is " << height << endl;
13  cout << "My grade is " << grade << endl;
14  cout << "Am I a programmer? " << boolalpha << isProgrammer << endl;
15
16  return 0;
17}

The code above declares variables of different data types and assigns them values. It then outputs the values using the cout statement. When using cout to output boolean values, the boolalpha manipulator is used to display true or false instead of 1 or 0.

By understanding the different data types in C++, you can effectively store and manipulate various types of data in your programs.

Next, we will explore control flow in C++ and learn how to use conditional statements and loops to control the flow of execution in our programs.

xxxxxxxxxx

#include <iostream>

using namespace std;

​

int main() {

  int age = 30;

  float height = 180.5;

  char grade = 'A';

  bool isProgrammer = true;

​

  cout << "My age is " << age << endl;

  cout << "My height is " << height << endl;

  cout << "My grade is " << grade << endl;

  cout << "Am I a programmer? " << boolalpha << isProgrammer << endl;

​

  return 0;

}

Control Flow in C++

Control flow refers to the order in which statements are executed in a program. In C++, control flow can be managed using conditional statements and loops.

Conditional Statements

Conditional statements allow you to perform different actions based on specific conditions. The most commonly used conditional statement in C++ is the if statement.

Here's an example of using an if statement to determine whether a number is even or odd:

1#include <iostream>
2using namespace std;
3
4int main() {
5  int num;
6  cout << "Enter a number: ";
7  cin >> num;
8
9  if (num % 2 == 0) {
10    cout << "The number is even." << endl;
11  } else {
12    cout << "The number is odd." << endl;
13  }
14
15  return 0;
16}

In the code above, the user is prompted to enter a number. The if statement checks if the number is divisible by 2 (i.e., the remainder is 0), and if so, it outputs that the number is even. Otherwise, it outputs that the number is odd.

Loops

Loops allow you to repeat a block of code multiple times. There are different types of loops in C++, including for loops, while loops, and do-while loops.

Here's an example of using a for loop to print the numbers from 1 to 5:

1#include <iostream>
2using namespace std;
3
4int main() {
5  for (int i = 1; i <= 5; i++) {
6    cout << i << " ";
7  }
8
9  return 0;
10}

In the code above, the for loop initializes a variable i to 1, checks if i is less than or equal to 5, executes the block of code inside the loop (printing the value of i and a space), and increments i by 1 in each iteration.

By using conditional statements and loops, you can control the flow of execution in your C++ programs and implement different logic based on specific conditions or repeat certain actions multiple times.

xxxxxxxxxx

#include<iostream>

using namespace std;

​

int main() {

  int num;

  cout << "Enter a number: ";

  cin >> num;

​

  if (num % 2 == 0) {

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

  } else {

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

  }

​

  return 0;

}

Functions in C++

In C++, a function is a block of code that performs a specific task. Functions are used to break down a program into smaller and more manageable pieces, making the code more organized and modular.

Defining a Function

To define a function in C++, you need to specify the function's return type, name, and parameters (if any). The return type indicates the data type of the value that the function returns, if any.

Here's an example of a function that calculates and returns the sum of two numbers:

1// Function to add two numbers
2int add(int a, int b) {
3  return a + b;
4}

In the code above, the function add takes two integer parameters a and b and returns their sum.

Calling a Function

To call a function in C++, you need to use the function name followed by parentheses. If the function has parameters, you need to provide the values for the parameters.

Here's an example of calling the add function from the previous example:

1int num1 = 5;
2int num2 = 10;
3int sum = add(num1, num2);

In the code above, the add function is called with the values of num1 and num2 as arguments, and the returned sum is stored in the variable sum.

Output

The console output of the above example will be:

1The sum of 5 and 10 is: 15

xxxxxxxxxx

#include <iostream>

using namespace std;

​

// Function to add two numbers

int add(int a, int b) {

  return a + b;

}

​

int main() {

  int num1 = 5;

  int num2 = 10;

  int sum = add(num1, num2);

​

  cout << "The sum of " << num1 << " and " << num2 << " is: " << sum << endl;

​

  return 0;

}