2 – Crunching Numbers

• Describe the meaning of assignment statements
• Use simple arithmetic expressions in assignment statements to calculate values
• Receive input from the keyboard and convert it to a numerical value

• Input
• output
• variables
• operators

• expressions
• integer and string
• execution
• walk-through

Last lesson, you…

• Defined what algorithms and programs are
• Wrote and executed your first Python programs (and weeded out syntax errors)

In this lesson, you will…

• Use arithmetic expressions to calculate values
• Use variables to store and reference values
• Follow walk-throughs of code and keep track of variable values
• Write programs that receive numerical input from the keyboard

• Assignments are not equations.
• This assignment does not mean that the days variable always equals 365.
• Assignments are instructions to be executed.
• The screenshot on the right is an instruction to assign the value 365 to the days variable.
• A subsequent assignment can assign a new value to the days variable, replacing the previous value.

• You can use expressions in assignments.
• This is an instruction to evaluate the expression on the right and then assign the value to the days variable on the left.
• A subsequent assignment can assign a new value to the days variable, replacing the previous value.

Symbol	Meaning	Examples	Meaning
+	addition	a + 1	a plus 1
–	difference	b – c	b minus c
*	multiplication	3 * d	3 times d
/	division	9 / 4	9 divided by 4 (value: 2.25)
//	integer division	15 // 2	quotient of 15÷2 (value: 7)
%	remainder of integer division	15 % 2	remainder of 15÷2 (value: 1)
**	exponentiation	2 ** 8	2 to the power of 8 (value: 256)

• An expression can refer to the values of variables.
• To evaluate this expression, the days variable must have been assigned a value.
• During program execution, a variable must have been assigned a value before that value is referred to.

• You will be given a program that is supposed to convert a length of time from seconds to minutes.
• Rearrange (change the order of) the statements, so that the program runs to completion without errors.

• Work on programs that receive numerical input from the keyboard and process it.
• Use the trinket.io assignment to follow the instructions on the worksheet.

In this lesson, you…

• Used arithmetic expressions to calculate values
• Used variables to store and reference values
• Followed walk-throughs of code and kept track of variable values
• Wrote programs that receive numerical input from the keyboard

Next lesson, you will…

• Use selection (if statements) to control the flow of program execution
• Introduce elements of randomness into your programs

• Complete the base tasks in activity 4 and upload the worksheet to bournetolearn.com.

• Complete the Gold badge tasks in the worksheet by adding some extra features to your code.

• Complete the Platinum badge tasks in the worksheet by changing how your weight on the moon is calculated.