Earlier you learned about C++ program structure. In this article, you will learn to write about your first C++ program and program elements in detail.
The meat of the C++ is in main function, and before main we need to declare the header files.
Simple C++ Program
Let us consider an example program and then we discuss the program elements in detail. The program declare a header file required for standard input and output operations called iostream.
#include <iostream.h>
void main(void)
{
//Variable declaration
int number;
// Reading input values
cout << "Enter the a number:" ;
cin >> number;
// if block
if (number > 100)
{
cout << "Number is greater than 100;
}
}The above program prints only when the number is greater than 100. That is, when the user input a number that is more than 100.
Variable Declaration
The main program begins with variable declaration. In C++ , you must declare your variable first and the syntax to declare the variable is:
<date_type> <indentifier1>, <identifier2>, ... <identifierN>;For example,
int A; // variable declared as integer type
char ID1, ID2,ID3; // variable declared as character type
float Number; // variable declared as floating type
Statements
A statement in C++ program perform some action. Every statement ends with a semi colon (;). The C++ statements can be divided into following category.
- Simple statements
- Expressions
- Statement blocks
Simple Statements – This type of statement are instruction to get input, print output or any one line statement that ends with a semi-colon.
For example,
cout<< ” Hello World ! “;
int number;
Sometimes a simple expression can also be a simple statement.
Expressions – An expression is a mathematical expression or an assignment that evaluates to a single value and ends with semi-colon. This type of statements use C++ operators.
For example,
result = number1 + number2;
area_of_triangle = ( 1/2 * base) * height;
We can write any type of complex expressions which depends on the problem we are solving.
Statement blocks – In the above program, if block is an example of statement block which encloses many simple statements.
For example,
if ( x == 0)
{
area = 0;
}
else
{
area = x * x;
}
cout << "Area = " << " " << area ;
}The example above has two blocks – if block and else block. The if block contains only one statement – an expession and the else block contains two statements.
This the advantage of grouping the statements into blocks, so that you can execute then as part of a task. The else block above computes the area and prints the result. Two actions were performed within a block.
Comments
C++ comments are lines ignored by the compiler. The compiler understands that the comments are not to be executed. The comments are of two types
- Single line comment (//)
- Multiline comment ( /* …. */)
Single Line Comment – You can write a single line of text as comment after (//) symbol. See the program above.
For example,
// this is a comment ignored by the compiler
// this is another line
Multiline Comment – Inherited from C language, C++ allows to add multiple lines as comments. Anything in between /* and */ is ignored. The multiple line comment is used for describing the program details. There is not restriction on white space or new line for multiline comments.
For example,
/*
Program Name: Tax Calculator
Program Author: Notesformsc.org
Program Description: The program receives inputs such as yearly income, tax rates and computes total tax payable by the employees.
Version: 1.0
*/
Common Mistakes While Writing C++ Programs
These are some common mistakes by beginners of C++ programming language.
- Forget to add necessary header files
- Spelling mistakes
- Not initializing the variables
- Not following a naming convention for variables.
- Forget to add semi-colon at the end of the statement
- Block is not closed
If you avoid the above mistakes , then you will have a clean and error free programs.
