Page 151 - Computer Science V2.0 Class 11

The following syntax describes the use of input()function to assign the user input to a variable. input() is used to
accept input from the user.
<variable> = input([<message-to-prompt-user-to-enter-input>])
The input() function reads the text entered by a user until a newline is encountered. In the above syntax description,
input is the keyword and message-to-prompt-user-to-enter-input is the message that is displayed on
the screen, followed by the cursor. Note that message-to-prompt-user-to-enter-input is enclosed within
square brackets, indicating that its use is optional. Indeed, we have already seen an example of the use of input()
function where we did not specify any message-to-prompt-user-to-enter-input. In the above description,
variable is to be replaced with a variable name. The function input() accepts user input from the keyboard.
On seeing the cursor, the user enters the required inputs and hits the enter key to indicate the end of input. Once
the user presses the enter key, the input() function yields the user input, which is assigned to the variable on the
left-hand side of the assignment operator. Python considers user inputs as strings. The use of the input() function
is illustrated below:

>>> rollNo = input('Enter your roll number: ')
Enter your roll number: 12
>>> name = input('Enter your name : ')
Enter your name: Kabir
>>> print(rollNo, name)
12 Kabir
In the above example, the variable rollNo is assigned the value 12 entered by the user. Similarly, the variable name
is assigned the value Kabir. As mentioned above, Python interprets the user inputs as strings. Thus, each
of the values 12 and Kabir, entered (by the user) is an example of a string. Next, suppose we wish to calculate the
perimeter of a rectangle based on the input length and breadth entered by a user.
>>> length = input('Enter length of rectangle: ')
Enter length of rectangle: 6
>>> breadth = input('Enter breadth of rectangle: ')
Enter breadth of rectangle: 4
>>> perimeter = (length + breadth)*2
>>> perimeter
'6464'
Recall that Python considers the user inputs entered interactively as strings. So, the variables length and breadth were
assigned the values '6' and '4' respectively. Therefore, (length + breadth) resulted in the string '64'. Finally,
(length + breadth)*2 resulted in '6464'. However, we were interested in the perimeter of the rectangle. So,
we need to convert length and breadth to numeric values before applying the arithmetic operations. This can
be done using the function int() as follows:

>>> perimeter = (int(length) + int(breadth))*2
>>> perimeter
20
Alternatively, we could transform the string inputs to integer values while reading from the user as follows:
>>> length = int(input('Enter length of rectangle: '))
Enter length of rectangle: 6
>>> breadth = int(input('Enter breadth of rectangle: '))
Enter breadth of rectangle: 4
>>> perimeter = (length + breadth)*2
>>> perimeter
20
6.6.2 print()

As the computer screen is the default device for displaying the results, the output produced on invoking the print()
function is displayed on the screen.

Basics of Python Programming 137