CSE 101 Lecture Notes - Lecture 4: Equals Sign, Concatenation, Newline
19 Jun 2018
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When we want to give a value to a variable, we write an assignment statement
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An assignment statement consists of a variable name, the equals sign, and a value or expression
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Number = 3 ("number is 3" or "number becomes 3")
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Total = 3.85 + 12.9
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First_name = 'Susan'
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Examples:
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These examples show three different data types: an integer, a real number, and a string
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Total = 5 + 8 + 3
.… other code here ….
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Total = 17 + 6
.… etc. .…
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After assigning a value to a variable, you can change the value of the variable with another
assignment statement:
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Next_year = this_year + 1
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Total_bill = subtotal + tax + tip
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Variables can also appear on the right-hand side (RHS) of an assignment statement:
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Assignment Statements
Suppose we wanted to compute the area of a square countertop with one corner cut off
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Assume that the triangular cut-out begins halfway along each edge
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If we needed to perform the computation only once, say for a 100 cm-long countertop, we might
write an expression like this: area = 100**2 - 50*50/2
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It's just a formula of sorts with no explanation of what the numbers mean
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The code only works for countertops exactly 100 cm long. What if we had countertops of
other sizes?
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Note that this code has a few issues with it:
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# area = area of square - area of triangle
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# area of triangle is 1/2 base*height
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area = 100**2 - 50*50/2
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Let's address the first issue: lack of clarity
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Comments are notes that the programmer writes to explain what the program does
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Comments do not affect the input or output of the program or anything about how it runs
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The lines beginning with the # symbol are called comments
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side = 100
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square = side**2
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triangle = (side/2)**2 / 2
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area = square –triangle
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Now let’s address the other issue: lack of generality
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To compute the area for a countertop of a different size, all we need to change is the first line:
side = 100
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This is an example of self-documenting code
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This code is also more readable; comments aren’t needed
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The spacing in between variables, numbers and operators is optional, but is included here to make
the formulas easier to read
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Example: Area Calculation
To improve this code even further, let’s make it interactive so that the user can provide the value
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Aside: Input Statements
Unit 2 - Computer Programming Fundamentals
Sunday, June 17, 2018
10:48 PM
CSE 101 Page 1
