In this tutorial, you will learn about C++ basics and some important notes on the main function.
C++ is a superset of the C language with extensions and improvements. Extensions are the new feature in the language, whereas improvements are better ways of doing that C already does. Below is an example of a very basic C++ program:
main() { }
It is the smallest possible C program as well. Because C++ is a superset of the C language, you can use a C++ compiler to develop and compile C programs.
C++ Basics: Hello World Program
The above minimum program does not do anything. It contains no more than one function, which as in C, must be named main
. Below is a C++ program that does something:
hello.cpp
#include <iostream.h> main() { cout << "Hello, world"; }
The hello.cpp
program includes iostream.h
and it uses an unfamiliar syntax with the undefined variable name cout
, the bitwise shift left operator (<<), and the only familiar part of the example, a literal string expression that greets the world.
Important Note
The above examples declare the main
function with no return type, which implies that the main
returns an integer, yet the main
functions in the examples have no return statement. The C++ language specification says that the main
function type is implementation-dependent. Traditionally, the main
returns an integer value, which the program returns to the system.
If the main
returns no value, the compiler assumes a void return, and the system receives an undefined return value when the program terminates by a return from the main
.
Some C++ compilers issue the warning. The Symantec C++ compiler issues an error and refuses to compile programs with main
functions that are declared to return something but do not return anything.
C++ Basics: Input/Output Streams
The C++ compiler products use classes to implement an improved stream input/output system. That design has become a de facto standard in C++ programs and is a part of the proposed standard C++. You use these improved streams to read and display information.
Standard Output Stream
The cout
variable, seen in the above example, is the C++ standard output stream, which writes to the console:
cout << "Hello, world";
The <<
operator is the output operator. It points symbolically from what is being sent to where it is going.
Standard Input Stream
For the input stream in C++, use the cin
object with >>
operator. Below is an example:
#include <iostream.h> main() { int amount; cout << "Enter an amount..."; cin >> amount; cout << "The amount you entered was " << amount; }
Output:
Enter an amount...74 The amount you entered was 74
In the above program, it sends a string to cout
to prompt you for input. The cin
device writes the value that you enter into the amount
integer variable. The exercise then displays the amount variable on cout.
Standard Error Stream
The cerr
object uses the same syntax as cout
, except that cerrs
output goes to the standard error device. This technique allows you to display error messages on the console.
C++ Basics: Comments
C++ supports the standard C comment format. The /*
character sequence begins a comment, and the */
sequence ends it. But C++ has another comment format. The C++ token is the double-slash (//
) sequence. Wherever this sequence appears, everything to the end of the current line is a comment. Below is an example:
#include <iostream.h> main() { /* C++ basics - comments example */ char name[20]; // declare a name string cout << "Enter a name..."; // request a name cin >> name; // read the name // display the name cout << "The name you entered was " << name; }
C++ Basics: Keywords
C++ reserves the standard C keywords and adds some of its own. The below list is having the standard C keywords and the common keywords that C++ adds. This tutorial is to just give the introduction of the C++ basics so I am not giving many details of each command for now. But in future posts definitely, you will be learning all about these keywords.
asm | double | new | switch |
auto | else | operator | template |
break | enum | private | this |
case | extern | protected | throw |
catch | float | public | try |
char | for | register | typedef |
class | friend | return | union |
const | goto | short | unsigned |
continue | if | signed | virtual |
default | inline | sizedof | void |
delete | int | static | volatile |
do | long | struct | while |
Conclusion
This post gave you the first exposure to the C++ basics. Mainly about the main
function and how it works in the C++ program, I/O streams, comments, and C++ keywords.