C++ program is a collection of objects which communicates each other via methods. It is a collection of statements which gets executed in a sequence, hence it is called a sequential programming language. Each statement is combination of various legal symbols. These symbols are smallest individual unit of a program. These are called as C++ tokens and classified into
- Keywords – re-existing, reserved words, each holding its own position and power and has a specific function associated with it. These can not be used as variable name.
- Identifiers – a name that identifies (that is, labels the identity of) a variable, arrays, functions, data structures, unique object and a unique class of objects.
- Constants/Literals – referred to as fixed values that cannot change their value during the entire program run as soon as we define them
- Strings – an array of characters as well as an individual data type.
- Operators – tools or symbols which are used to perform a specific operation on data. Operations are performed on operands.
- Special Symbols – [] () {} , # * ~ . are special symbols, which help you manipulate or perform data operations. Each special symbol has a specific meaning to the C++ compiler.
Rules for C++ Identifiers
There are certain rules to be followed by the user while naming identifiers, otherwise, you would get a compilation error. These rules are:
- First character: The first character of the identifier in C++ should positively begin with either an alphabet or an underscore. It means that it strictly cannot begin with a number.
- No special characters: C++ does not encourage the use of special characters while naming an identifier. It is evident that we cannot use special characters like the exclamatory mark or the “@” symbol.
- No keywords: Using keywords as identifiers in C++ is strictly forbidden, as they are reserved words that hold a special meaning to the C++ compiler. If used purposely, you would get a compilation error.
- No white spaces: Leaving a gap between identifiers is discouraged. White spaces incorporate blank spaces, newline, carriage return, and horizontal tab.
- Word limit: The use of an arbitrarily long sequence of identifier names is restrained. The name of the identifier must not exceed 31 characters, otherwise, it would be insignificant.
- Case sensitive: In C++, uppercase and lowercase characters connote different meanings.
List Of Special Symbols
Special Character | Trivial Name | Function |
| [ ] | Square brackets | The opening and closing brackets of an array symbolize single and multidimensional subscripts. |
| () | Simple brackets | The opening and closing brackets represent function declaration and calls, used in print statements. |
| { } | Curly braces | The opening and closing curly brackets to denote the start and end of a particular fragment of code which may be functions, loops or conditional statements |
| , | Comma | We use commas to separate more than one statements, like in the declaration of different variable names |
| # | Hash / Pound / Preprocessor | The hash symbol represents a preprocessor directive used for denoting the use of a header file |
| * | Asterisk | We use the asterisk symbol in various respects such as to declare pointers, used as an operand for multiplication |
| ~ | Tilde | We use the tilde symbol as a destructor to free memory |
| . | Period / dot | The use the dot operator to access a member of a structure |
Comments
Explanatory statements, included in the C++ code, help anyone reading the source code.
Like any other language C++ supports comments and classifies comments into single-line and multi-line comments. All characters available inside any comment are ignored by C++ compiler.
C++ comments start with /* and end with */. For example −
/* This is a comment */ /* C++ comments can also * span multiple lines */
A comment can also start with // extending to the end of the line.
#include <iostream>
using namespace std;
main() {
cout << "Hello World"; // prints Hello World
return 0;
}
When the above code is compiled, it will ignore // prints Hello World and final executable will produce the following result −
Within a /* and */ comment, // characters have no special meaning. Within a // comment, /* and */ have no special meaning. Thus, you can “nest” one kind of comment within the other kind. For example −
Hello World
/* Comment out printing of Hello World: cout << "Hello World"; // prints Hello World */
