Standard Input Output Stream

C++ Standard Input Output Stream

In this C++ tutorial, you will learn about standard input stream and standard output stream explained along with syntax and examples.

C++ programming language uses the concept of streams to perform input and output operations using the keyboard and to display information on the monitor of the computer.

What is a Stream?

A stream is an object where a program can either insert or extract characters to or from it. The standard input and output stream objects of C++ are declared in the header file iostream.

Standard Input Stream

Generally, the device used for input is the keyboard. For inputting, the keyword cin is used, which is an object. The overloaded operator of extraction, >>, is used on the standard input stream, in this case: cin stream. Syntax for using the standard input stream is cin followed by the operator >> followed by the variable that stores the data extracted from the stream.

For example:

Int prog;
cin >> prog;

In the example above, the variable prog is declared as an integer type variable. The next statement is the cin statement. The cin statement waits for input from the user’s keyboard that is then stored in the integer variable prog. 

The input stream cin wait before proceeding for processing or storing the value. This duration is dependent on the user pressing the RETURN key on the keyboard. The input stream cin waits for the user to press the RETURN key then begins to process the command. It is also possible to request input for more than one variable in a single input stream statement. A single cin statement is as follows:

cin >> x >> y;

is the same as:

cin >> x;
cin >> y;

In both of the above cases, two values are input by the user, one value for the variable x and another value for the variable y.

// This is a sample program         This is a comment Statement #include <iostream.h>                  Header File Inclusion Statement void main() { int sample, example; cin >> sample; cin >> example; }

If a programmer wants to write comments in C++ program, the comments should follow after a pair of slashes denoted by //. All the characters after the // are ignored by C++ compiler and the programmer can choose to comment after the //.

In the above example, two integer variables are input with values. The programmer can produce input of any data type. It is also possible to input strings in C++ program using cin. This is performed using the same procedures. The vital point to note is cin stops when it encounters a blank space. When using a cin, it is possible to produce only one word. If a user wants to input a sentence, then the above approach would be tiresome. For this purpose, there is a function in C++ called get line.

Standard Output Stream

By default, the device used for output is the screen of the computer. For outputting values the keyword cout is used, which is an object. The insertion operator << is used on the standard output cout stream.  The syntax for using the standard output stream is cout followed by the operator << followed by the value to be inserted or output by the insertion operator.

For example:

Int prog;
cin >> prog;
cout << prog;

In the above example, the variable prog is declared as an integer type variable. The next statement is the cin statement that waits for input from the user’s keyboard. This information is then stored in the integer variable prog. The value of prog is displayed on the screen by the standard output stream cout.  It is also possible to display a sentence as follows:

Cout << “Training given by Item”;

The above gives output as:

Training given by Item

If a programmer chooses to use constant strings of characters, they must be enclosed between double quotes “”.

In this situation, it is important to note the difference between the two statements below:

Cout << "item";
cout << item;

In the above, the first statement displays on the screen as item. The second statement outputs the value of the variable item.  As previously explained, the extraction operator >> can be used more than once in a single cin statement. Similarly, it is possible to use the insertion operator << more than once in a cout statement.

For example

Cout << "Item" << "gives" << "excellent training";

This produces output on the screen as:

Item gives excellent training

The above concept is mainly used if the programmer chooses to print string constants followed by variables.

In this next example, the programmer chooses to display a combination of string constants and variables.

For example

int a=50; cout << "Item has given" << a << "numbers of trainings";

This produces the output as:

Item has given 50 numbers of trainings

Below is one more example:

cout << “Item”; cout << “Training”;

The above produces output as:

Item Training

An important point to note from the above example is cout does not give a line break unless specified.  If the programmer chooses to display output in a new line, it must be explicitly specified in cout by using the \n which denotes newline character.

For example

Cout << "Item\n ";
cout << "Training";

Gives output as

Item
Training

There is also another way for specifying newline that is by using endl manipulator.

For example

cout << "Item" << end;
cout << "Training";

Gives the same output as

Item
Training

Example to demonstrate the use of input and output streams

// Example to demonstrate the use of Input and Output streams #include <iostream.h> void main() {    int a,b;    cout << “Enter the value of a:”;    cin >> a;    b=a+10;    cout << “Value of b is:”<<b;