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Simple Input

December 9, 2016

Remember the traditional program flow: 


Input -> Processing -> Output


Input is defined in this context as data the user gives to the program. The program then uses that data in some way - manipulates it or just stores it in memory. Finally the program creates output. A program without output would be downright boring.


Picture a program that asks a user for his or her name and responds appropriately: 

(in this example, the user input is italicized)


What is your name?


Hello, Michael! Have a good day.


The first line is called the prompt - some output that elicits user input. The user inputs his name which is stored in the computer's memory. Finally the program uses that input in an output line.


Here's a short program to achieve this goal: 


name=input("What is your name?")

print("Hello, %s! Have a good day." % name)


Points to note: 

name is a variable. You know that because it is on the left side of the equal sign. 

input() produces a value. You know that because it's on the right side of the equal sign. Actually it "returns" a value.

name's type is str or String. The input() function always gives you strings, even if you input numbers. Try this one to see the error it produces. 


age=input("What is your age?")

print("In 5 years you'll be %i years old." % age+5 )


It says that %i is for ints but you seem to want a string there. Go ahead and change the %i to a %s and see the familiar error message. 


In this case you'll need a cast.


Next Post: Dealing With Input as a String


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