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Learn C++: The Complete Course for Beginners

Variables in C++

Explore how to declare and initialize integer variables in C++, learn about identifiers, and see practical examples of updating variable values within a program. This lesson helps you grasp fundamental variable concepts needed for effective C++ coding.

We'll cover the following...

Variable declaration

A variable declaration means that we want the compiler to reserve a space for a data with the given name and type.

The basic syntax for declaring a variable in C++ is:

📝Note: Don’t worry about the data types yet. We will cover these in detail in the next chapter. For this chapter, we will just work with int. int is used to store an integer value in a variable. A variable declared with an int data type cannot store floating-point values.

To declare a variable that can store an integer value, we will write the following line:

C++
#include <iostream>
using namespace std;
int main() {
  int number;
}

In the above line, we have declared a variable with the name number, and it can store data of type int. Here, the number is an identifier.

We can declare more than one variable in a single line.

int number1, number2, number3;

The above line declares three variables: number1, number2, and number3.

Variable initialization

Variable initialization means to actually store value in the reserved space.

The basic syntax for initializing a variable in C++ is given below:

In C++, we will write the following lines for initializing the variable of integer type:

C++
#include <iostream>
using namespace std;
int main() {
  int number;
  number = 100;
}

In the above code, we have defined the variable number that can store integer values, and it is assigned an initial value of 100.

💡Do you know? C++ is a statically-typed language. In a statically-typed language, a variable is declared with its type before its first use.

Variable declaration and initialization in one step

At this point, you’re probably wondering if you can simply just declare a variable and assign it a value in one go? The answer is yes! We can do this in the following way:

C++
#include <iostream>
using namespace std;
int main() {
  int number = 100;
}

Example program

We can use a variable to keep track of the current amount in our bank account. Suppose you have $100 in your bank account. After some time, your friend transfers $20 to it. Now, the current amount is $120. Let’s write a code in C++ that can keep track of your account balance.

Run the code below and see the output!

C++
#include <iostream>
using namespace std;
int main() {
  // Declares a variable current_amount
  int current_amount;
  // Initialize a variable current_amount to 100
  current_amount = 100;
  // Prints the value of current_amount
  cout << "Your current amount is: " << current_amount << endl;
  // Updates the value of current_amount
  current_amount = 120;
  // Prints the updated value of current_amount
  cout << "Your current amount is: " << current_amount << endl;
}

Line No. 7: Declares a variable current_amount that will store the integer value.

Line No. 9: Initially, there is $100 in a bank account. Therefore, we store 100 in variable current_amount.

Line No. 11: Displays the value of current_amount.

📝 To print the value of a variable, use cout followed by the insertion operator << and variable name.

Line No. 13: When your friend transfers $20 to your account, the current_amount becomes $120. Therefore, we update the value of the current_amount to 120, changing the value of a variable during the program execution.

Line No. 15: Displays the updated value of current_amount.

Quiz

1.

In which of the following ways can we declare and initialize a variable var with a value of 1000?

(You can select multiple correct answers) Multi-select

A.

var = 1000;

B.

int var;

var = 1000;

C.

int var = 1000;

D.

int var = 1000

1 / 1

Interesting so far? Let’s move on to the next lesson where we will discuss identifiers in C++.