Variable declaration and initialization in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a variable declaration in C++?

A variable declaration tells the computer to create a space in memory to store a value of a specific type, but it does not assign a value yet.

beginner

What does variable initialization mean?

Variable initialization means giving a variable its first value at the time it is created.

beginner

How do you declare and initialize an integer variable named age with the value 25 in C++?

You write: int age = 25; This creates the variable age and sets its value to 25.

intermediate

What happens if you declare a variable without initializing it?

The variable has an undefined value (garbage) until you assign a value to it. Using it before assignment can cause errors.

intermediate

Show two ways to initialize a variable in C++.

1. Using assignment: int x = 10;<br>2. Using constructor style: int x(10);

Which of the following is a correct variable declaration and initialization in C++?

A number = 5;

B int number = 5;

C int number;

D int = 5 number;

Option B declares an integer variable named 'number' and initializes it with 5. Option C declares but does not initialize. Option A is an assignment without declaration. Option D is invalid syntax.

What is the value of an uninitialized local variable in C++?

A Compiler error

B Zero

C Always one

D Undefined (garbage value)

Local variables not initialized have undefined values, which means they contain whatever was in memory before.

Which keyword is used to declare a variable in C++?

A int, float, char (type names)

B let

C declare

D var

In C++, variables are declared by specifying their type like int, float, char, etc.

What does this line do? double price(19.99);

A Declares and initializes price with 19.99

B Declares a double variable named price without value

C Assigns 19.99 to an existing variable price

D Syntax error

This is constructor-style initialization of the variable price with the value 19.99.

Which of these is NOT a valid variable name in C++?

A total_sum

B value3

C 2ndValue

D _count

Variable names cannot start with a number, so '2ndValue' is invalid.

Explain the difference between variable declaration and variable initialization in C++.

Think about creating a box versus putting something inside it.

Write an example of declaring and initializing a variable of type float with the value 3.14.

Use the syntax: type name = value;