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Keywords and Identifiers in C++

1. What is Keywords and Identifiers in C++?​

Keywords:​

  • Keywords are predefined words that have special meanings to the C++ compiler.
  • They are part of the language syntax and serve specific purposes.
  • They are always written in lowercase in C++.
  • It have a fixed set(around 32 in C++)that doesn't change.
  • For example, int, if, while, and class are keywords.
  • Keywords cannot be used as identifiers (variable names, function names, etc.) because they already have predefined meanings.

Identifiers:​

  • Identifiers are unique names given to variables, functions, classes, and other entities by the programmer.
  • They help us create meaningful and descriptive names for program elements.
  • Examples of identifiers: money, accountBalance, studentAge, and calculateSum.
  • Must follow the below specific naming rules:

Rules for naming identifiers:​

  • Can consist of letters (A-Z or a-z), digits (0-9), and underscores (_).
  • Must begin with a letter or an underscore.
  • Are case-sensitive (e.g., Num and num are different).
  • Cannot use reserved keywords as identifiers.
  • Must be unique within their namespace (e.g., no two variables with the same name in the same scope)31.

2. Why do we use Keywords and Identifiers in C++?​

we use keywords:​

  • Syntax: Keywords define the syntax and structure of the language. They help the compiler understand the code.
  • Reserved Meanings: Each keyword has a reserved purpose (e.g., if for conditional statements, while for loops, class for defining classes).
  • Consistency: Using keywords ensures consistency across different C++ programs.
  • Efficiency: Keywords allow the compiler to optimize code execution.
  • Readability: They make the code more readable and self-explanatory.

we use identifiers:​

  • Descriptive Names: Identifiers give meaningful names to program entities (e.g., totalAmount, calculateAverage).
  • Readability: Well-chosen identifiers enhance code readability for both programmers and collaborators.
  • Avoid Magic Numbers: Instead of using raw numbers (e.g., 42), we use identifiers (e.g., MAX_SCORE) to make the code self-documenting.
  • Modularity: Identifiers help organize code into logical units (functions, classes, etc.).
  • Avoid Confusion: Descriptive identifiers prevent confusion and improve maintainability.

3. Write a simple program to demonstrate the use of Keywords and Identifiers in C++.​

#include <iostream>

using namespace std;

int main() {
  // Integer variable to store age (identifier)
  int age = 25;

  // `if` is a keyword for conditional statement
  if (age >= 18) {
    cout << "You are eligible to vote." << endl;
  }

  // `for` is a keyword for loop
  for (int i = 0; i < 3; i++) {
    cout << "Iteration: " << i << endl;
  }

  // `double` is a keyword for floating-point numbers (identifier)
  double pi = 3.14159;
  cout << "Value of pi: " << pi << endl;

  // `calculateArea` is a user-defined identifier (function name)
  int area = calculateArea(5, 4); // Assuming calculateArea is defined elsewhere
  cout << "Area of rectangle: " << area << endl;

  return 0;
}

// This function (identifier) is not defined here, but for demonstration purposes
int calculateArea(int length, int width) {
  return length * width;
}

keywords-and-identifiers-in-cpp

4. List of Keywords in C++​

C++ has a set of around 32 keywords that have special meanings within the language. Here's a list for your reference:

  • Basic data types: int, float, double, char, bool
  • Storage specifiers: auto, register, static, extern
  • Type specifiers: void, const, volatile
  • Control flow: if, else, for, while, do, switch, case, break, continue, return
  • Function definitions: inline, friend, virtual
  • Object-oriented programming: class, struct, public, private, protected, this, new, delete
  • Exception handling: try, catch, throw
  • Other: sizeof, namespace, template, typedef Note: This is not an exhaustive list, and the exact number of keywords may vary slightly depending on the C++ version you're using. It's always a good practice to refer to the official C++ documentation for the latest keyword definitions.

5. Rules for defining Identifiers in C++​

Remember these rules when defining identifiers:

  • Must start with a letter or underscore. Cannot start with a digit.
  • Consist of letters, digits, and underscores.
  • Avoid using reserved keywords as identifiers.
  • Be case-sensitive (e.g., myVar and MyVar are different).
  • No limit on the length of an identifier.
  • Cannot be the same as keywords in C++.

6. Examples of Identifiers in C++​

Valid Identifiers:​

  • Starts with letter or underscore age, _temporary, myObject
  • Can contain letters, digits, and underscores calculate_area, x123
  • Case-sensitive age, Age
  • Cannot be a keyword cpp_keyword (not recommended)

Invalid Identifiers:​

  • Starts with a number 1st_place
  • Contains hyphen my-function
  • Keywords int,while

7. Difference between Keywords and Identifiers in C++​

  • Keywords are predefined words with specific meanings in the language , while identifiers are user-defined names for program elements.
  • Keyword can control flow and structure but Identifiers, identify program elements.
  • Keywords cannot be used as identifiers.On the other hand, identifiers used for variables , functions , classes , etc.
  • Keywords have fixed set, lowercase only but , identifiers defined by programmer , case sensitive.
  • Examples of keyword: int,if,while,class.
  • Examples of identifier: age,calculateArea,myObject.