1. Variables and Assignment CSIS 1595: Fundamentals of Programming and Problem Solving 1

2. Computing and Memory • All computing in terms of memory locations • Storing values into locations in memory • Readingvalues from locations in memory • Example: Converting Celsius temperature to Fahrenheit • Get Celsius temp from user, store in location 1 • Compute 1.8 x value in location 1, add 32, store in location 2 • Output value in location 2 to user

3. Variables • Variable name given to location in memory • Example: Converting Celsius temperature to Fahrenheit • Get Celsius temp from user, store in celsius_temperature • Compute 1.8 x celsius_temperature+ 32, store in fahrenheit_temperature • Output value of fahrenheit_temperatureto user

4. Namespaces • Python environment / operating system maps variables to locations in memory • Namespace: list of variables and corresponding values currently active in Python environment • Variable added to namespace when first used • Other languages require variable to be declared first • Can use id(variable) function to find actual numeric id Python uses for variable

5. Naming Variables • Rules (different in other languages) • Must start with letter or underscore • Rest may contain letters, underscores, and digits • Cannot contain spaces or other characters • Case sensitive • Cannot be Python keyword • Should be descriptive (readability)

6. Assignment • Storing values into variables • Syntax: variable = expression • Expression evaluates to a value • That value stored in the variable • Not same as = in math!x = 7 assigns the value 7 to x7 = x not legal!

7. Expressions • Expressions (on RHS of assignment) may contain: • Literals (fixed values) • Numbers 2, 3.5, -12.6, etc. • Strings (must be inside quotes) “John” • Booleans True, False • Variables • Must have already been assigned a value! • Functions • Must return a value

8. Functions • Predefined code with action based on list of arguments • Syntax: functionname(list of arguments) • multiple arguments separated by commas • May return a value (so can be part of expression) • Examples: • print(list of strings) Displays strings separated by spaces • input(prompt) Displays prompt, returns value entered by user • id(variable) Returns numeric id of variable in namespace

9. Expressions and Operators • Variables, literals, functions can be combined using operators • Most are binary operators combining 2 operands • Exception: unary minus sign -12 • Syntax: operandoperator operand • Example: Can append two strings using +string3 = string1 + string2

10. Example # Prompt the user for their first and last name first_name = input(“What is your first name? ”) last_name= input(“What is your last name? ”) # Combine the two into a full name # (separated by a space) full_name = first_name + “ “ + last_name # Display greeting to user with their full name print(“Hello”, full_name)