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Input and Output
Upsorn Praphamontripong
CS 1110
Introduction to Programming
Spring 2017
Program Development Cycle
Design the
program
Write the
code
Correct
syntax errors
Test the
program
review
Correct
logic errors
• Understand the task the program will perform
• Break down the task into a series of steps
• Algorithm
• Translate an algorithm into code
• Two Representation
• Pseudocode
• Flowchart
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Algorithm  Pseudocode
review
Exercise:
Get 2 numbers from the user and display the larger number
Algorithm:
1. Get the first number
2. Get the second number
3. Compare the 2 numbers
4. Display the larger number
CS 1110
Pseudocode:
1. Input the first number
2. Input the second number
3. If the first number > the second
number, display the first number
4. Otherwise, display the second
number
(what if the first number is equal to the
second number?)
3
review
Algorithm  Flowchart
Exercise:
Get 2 numbers from the user and display the larger number
Start
Algorithm:
1. Get the first number
2. Get the second number
3. Compare the 2 numbers
4. Return the larger
number
Input the
first number
Input the
second number
Yes
the first number
is greater than
the second number
Display the
first number
No
Display the
second number
End
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Input – Process – Output
Exercise:
Get 2 numbers from the user and display the larger number
Input
The first
number
The second
number
input() function
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Process
Output
Check if the first number
is greater than
the second number
The larger
number
print() function
5
Reading Input from the Keyboard
input(prompt)
input(“What is your name? ”)
• Display the string “What is your name? ” on the screen
• Wait for the user to enter something and press Enter
• The user’s input is returned as a string
name = input(“What is your name? ”)
• The user’s input is returned as a string and assigned to the variable
name
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Variables
• A name that represents a value stored in the computer’s
memory
• Creating variables with assignment statements
statement = "Python is awesome!!!!"
Assignment operator
statement
• Python is dynamic typed language
Python is awesome
String literal
statement = "Python is awesome!!!!”
statement = 4
Numeric literal
Type: string
Type: int
Variable reassignment
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Variable Naming Rules
• No Python’s key words
• No spaces
• First character must be one of the letters (a…z or A…Z)
or an underscore character ( _ )
• Case sensitive
• Descriptive
• Consider t (or x) vs temp vs temperature
• How about payrate vs pay_rate vs payRate
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Displaying Output on the Screen
print(zero or more parameters)
print(“Hello World”)
• Display the string “Hello World” on the screen
print(“Hello ” + ”World”)
• Display the string “Hello World” on the screen
print(“Hello”, ”World”)
• Display the string “Hello World” on the screen
print()
• Display an empty line
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How about
print(print())?
9
Strings and String Literals
• String = a sequence of characters
• E.g., “Hello World”
• String literal = a value/string that appears in a program, the
actual value of the thing it represents
• E.g., print(“Hello World”)
• Must be surrounded by quotation marks
• Quotation marks used
• print("Python is awesome!")
• print('Python is awesome!')
• print('"Python is awesome!"')
• print('Python\'s awesome!')
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