Statements and Expressions in C++

In C++ programming, statements and expressions are the building blocks of your code.

Expressions

An expression is a piece of code that evaluates or calculates a value. It consists of variables, constants, and operators (+, -, *, /, etc.) combined in a meaningful way. Think of expressions as a simple math equation or a question that the program needs to answer.

Here are some examples of expressions:

5 + 3 // add
x * y // multiply
a > b // comparison

Statements

A statement, on the other hand, is a complete line of code that performs an action. It usually consists of one or more expressions joined together. Statements end with a semicolon (;), which tells the compiler that the line is complete.

Here are some examples of statements:

int x = 5; // Declaration and assignment statement
x = x + 3; // Assignment statement
std::cout << x; // Output statement (or function call)

Types of Statements

C++ has several types of statements, including:

1. Declaration Statements: These statements declare and define variables and their types. For example:

   int age; // Declares an integer variable named 'age'
   std::string name; // Declares a string variable named 'name'
   

2. Assignment Statements: These statements assign a value to a variable. For example:

   age = 25;
   name = "John Doe";
   

3. Control Statements: These statements control the flow of your program, such as loops and conditional statements. For example:

   if (age > 18) {
       std::cout << "You are an adult!";
   } else {
       std::cout << "You are a child!";
   }
   
   // Subtract age until it is no longer greater than 0.
   while (number > 0) {
       std::cout << number << std::endl;
       number--; // Equivalent to `number = number - 1;`
   }
   

4. Function Call Statements: These statements call or invoke a function in your program. For example:

   int result = add_numbers(5, 3); // Calls the 'add_numbers' function with arguments 5 and 3
   

Combining Statements and Expressions

In C++ programs, you'll often see expressions and statements combined. For example:

int x = 5; // Declaration and assignment statement
int y = x * 2 + 1; // Declaration, assignment, and expression combined

In this example, the expression x * 2 + 1 is combined with the declaration and assignment statement to create a new statement.