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CS1 Python Subgoals

Section 2.4 Basic Knowledge

Subgoals for evaluating an assignment statement.

  1. Decide order of operations
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    1. Decompose as necessary
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  2. Determine operator behavior based on operands
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    1. Operator and operands must be compatible
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  3. Solve arithmetic, expression, or operation
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    1. Decompose as necessary
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Subsection 2.4.1

Given the following code snippet, evaluate the final statement (the last line). If invalid, give the reason. If valid, what value is assigned to the variable?
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alpha = 2
beta = 3.0
delta = 3
gamma = alpha + delta
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Subsection 2.4.2 SG1: Decide order of operations

There is only one operator (an addition +) so that will be evaluated first.
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Subsection 2.4.3 SG2: Determine operator behavior based on operands

The expression alpha + delta is an addition between two integer values. This is a valid operation, and will produce an integer.
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Subsection 2.4.4 SG3: Solve arithmetic, expression, or operation

The variable alpha is substituted for the value 2 and the variable delta is substituted for the value 3. Adding them together produces the value 5. This value is stored in gamma.
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Subsection 2.4.5 Questions to check understanding

  1. Is the left-hand-side (LHS) of the statement a variable? What type?
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    Answer.
    Yes, the variable gamma holds an integer value.
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  2. What is the resulting type after evaluating the right-hand-side (RHS)?
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    Answer.
    The RHS evaluates to an integer.
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  3. Would adding beta instead of delta instead change the resulting type?
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    Answer.
    Yes, the variable beta holds a float value, and adding together a float and an integer produces a float instead of an integer.
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