C++ Syntax

Syntax is the set of rules that defines how C++ statements, expressions, functions, classes, and other language elements must be written.

int age = 20;

The above statement follows valid C++ syntax.

#include <iostream>

int main() {

    std::cout << "Hello C++";

    return 0;
}

A simple program can contain a header, the main function, statements, and a return statement.

A statement is an instruction that tells the program to perform an operation.

int age = 20;
std::cout << age;

Many C++ statements end with a semicolon.

The semicolon ; is used to terminate many C++ statements.

int number = 10;
std::cout << number;

Forgetting a required semicolon can result in a compilation error.

Curly braces { } are used to define blocks of code. Functions, loops, conditional statements, classes, and other constructs can contain blocks.

int main() {

    std::cout << "Hello";

}

The main() function is the normal entry point of a C++ program.

int main() {

    return 0;
}

Execution of a normal C++ program begins from main.

Header files provide declarations and facilities that can be used by a C++ program.

#include <iostream>

The iostream header is commonly used for standard input and output streams.

The #include directive is a preprocessor directive used to include a header.

#include <iostream>

This makes declarations from the selected header available during compilation.

Keywords are reserved words that have special meaning in the C++ language.

Examples include:

• int
• if
• else
• for
• while
• class
• return

int age = 20;

Here, int is a C++ keyword.

Identifiers are names given to program elements such as variables, functions, classes, and objects.

int studentAge = 20;

Here, studentAge is an identifier.

Common rules for C++ identifiers include:

• They can contain letters, digits, and underscores.
• They cannot begin with a digit.
• They cannot contain spaces.
• They cannot be C++ keywords.
• They are case-sensitive.

studentName
student_name
age2

Valid identifiers:

age
studentName
student_name
number1

Invalid examples:

2number
student name
class

The first two invalid examples violate identifier rules, while class is a reserved keyword.

C++ is case-sensitive. Uppercase and lowercase letters are treated as different characters.

int age = 20;
int Age = 30;
int AGE = 40;

Here, age, Age, and AGE are different identifiers.

Comments are notes written in source code. They are ignored as executable code.

Single-line comment:

// This is a comment

Multi-line comment:

/*
   This is a
   multi-line comment
*/

A single-line comment starts with // and continues until the end of the line.

int age = 20; // Student age

The text after // on that line is treated as a comment.

Multi-line comments begin with /* and end with */.

/*
   This program
   displays a message.
*/

They can span multiple lines.

Text is commonly written inside double quotation marks.

std::cout << "Hello C++";

The text Hello C++ is a string literal.

A character literal is commonly written inside single quotation marks.

char grade = 'A';

Here, 'A' is a character literal.

Numbers can be written directly in C++ source code.

int age = 20;
double price = 99.50;

Here, 20 and 99.50 are numeric literals.

A variable can be declared and assigned a value using valid C++ syntax.

int age = 20;

Here, int specifies the type, age is the variable name, and 20 is the initial value.

Operators are symbols used to perform operations on values and variables.

int sum = a + b;

The + operator performs addition in this expression.

An expression is a combination of values, variables, operators, and other elements that produces a value.

int result = a + b * 2;

The right side of the assignment contains an expression.

The if statement is used to execute code when a condition is true.

if (age >= 18) {

    std::cout << "Adult";

}

The condition is written inside parentheses.

A for loop contains an initialization, condition, and update expression.

for (int i = 1; i <= 5; i++) {

    std::cout << i;

}

A function declaration or definition includes a return type, function name, parameter list, and function body.

int add(int a, int b) {

    return a + b;

}

Here, int is the return type and add is the function name.

C++ uses namespaces to organize names and reduce naming conflicts. The standard library uses the std namespace.

std::cout << "Hello";
std::string name = "Rahul";

The std:: prefix specifies the standard namespace.

Spaces, tabs, and line breaks can improve readability. Proper indentation makes the structure of a program easier to understand.

if (age >= 18) {

    std::cout << "Adult";

}

Consistent formatting is especially useful when programs become large.

Common beginner syntax mistakes include:

• Missing semicolons
• Missing braces
• Missing quotation marks
• Misspelled keywords
• Incorrect capitalization
• Incorrect parentheses
• Using an invalid identifier

std::cout << "Hello"   // Missing ;

#include <iostream>

int main() {

    int age = 20;

    if (age >= 18) {

        std::cout << "You are an adult.";

    } else {

        std::cout << "You are a minor.";

    }

    return 0;
}

This example demonstrates headers, the main function, variables, conditions, braces, statements, operators, and output.

Learning these basic syntax rules will make it easier to understand the remaining C++ lessons.