13.1. Using Decisions with Strings

We can use conditional statements in code to produce different strings for different situations and to treat different strings in different ways. As a first example, here is a program that prints a different message depending on how many item(s) a person orders. Try this program a few times and enter different values for the input.

numItems = int( input("How many items do you want?") ) if numItems > 1: message = "You ordered " + str(numItems) + " items" elif numItems == 1: message = "You ordered 1 item" else: message = "That is not a valid number to order!" print(message)

In the program, notice that we have to use the int function to turn the input from a string into an integer. Anytime we use input to get some input from the user, it will be read as a string. If the user types 20, that will be stored by Python as the string "20" and not as the numeric value 20. Any time we get input, if we want to work with it as a number and not as a string (a piece of text that may have digits in it) we will need to use this trick.

Similarly, when we go to construct the string that is the elif response, we are trying to combine the string "You ordered " with numItems a number. As we have seen before, to make this work, we need to call the str function to make a string out of the number that can be added to the other strings.

What will happen if you change the first line to remove the int function by making it numItems = input("How many items do you want?")?

• It runs the same
• Try it!
• It sometimes produces the wrong answer because it is comparing a string to a number
• Try it!
• There is an error because we are comparing a string to a number
• Correct. You are not allowed to compare a string to a number. Even if the string is something like "2" that looks like a number.

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