COMP 171: Data Types John Barr

Review - What is Computer Science? Problem Solving  Recognizing Patterns  If you can find a pattern in the way you solve different instances of a problem, you can create an algorithm so the computer can solve the problem for you.

Review - What is Computer Science? An Algorithm  Step-by-step procedure to solve the problem from beginning (start state) to end (end state)  Sequential  Some steps can repeat  High level: only list important details

Values Fundamental building block in a programming language Values are the “things” that we save and manipulate There are only a few basic types of values …but we can make our own types of values

Data Types in Python Integers  whole numbers, positive or negative (5, 42, -7) Floats  Decimal numbers ( , ) Strings  sequences of characters (‘dog’, “cat”, ‘’’rat’’’, ‘17’, “23.5” ) classes and types are the same thing (for now) Can use one two or three quotes

Variables A way to name a place in memory for data Legal Names:  No spaces  Can’t start with a number start with letter or underscore  Can’t use keywords middle of "Variables, Expressions and Statements" chapter for list e.g., class, int  Don’t use symbols $, %, # illegal

Variables Takes a value, and assigns it a variable age = 18 #puts the int 18 into the variable age name = "Joe" #puts the string "Joe" into the variable name Can be reused  age = 87 changes the value in the variable age

Variables What’s currently in a variable  Interpreter: just type variable name and return  Program: use the print() function

Input Takes a string in from the keyboard  always a string, even if you enter a number temp = input() #gets a string and saves into variable temp

Input Problem: input always returns a string. What if we want to get a number?  age = input(“Enter your age”)  type(age) Must convert to the type we want int (string), float(string), str(int or float)

Debugging – finding errors / faults syntax errors runtime errors semantic errors

Comments Programs can get very long and convoluted. Sometimes we’d like to put in some words to explain what we’re doing python comments start with the # character.  everything on the line after the # is ignored

Practice Write a program that creates a variable for your name and a variable for your age, and prints a sentence like this:  Toby is 32

Practice Add code to calculate and print your age in decades:  That's 3.2 decades

Practice Get first name from the keyboard

Practice Get age from the keyboard