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SECTION 08 / 15
Procedures, parameters and return values
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A procedure is a named set of steps we can reuse. Think of asking a helper to do one well-defined job. Parameters tell the helper which version of the job to do. A return value brings the answer back.
Separate a value from a field name
In SumMarks(F, Mathematics), F is a value used in a comparison with Gender. Mathematics is the name of the field to extract. Inside the procedure, the parameter GenderValue receives F and Field receives Mathematics. X[Field] means “read the field whose name is stored in Field”.
Procedure SumMarks(Rows, GenderValue, Field)
Sum = 0
for each row X in Rows {
if (X.Gender == GenderValue) {
Sum = Sum + X[Field]
}
}
return Sum
End Procedure
GirlsMaths = SumMarks(Scores, "F", "Mathematics")
BoysMaths = SumMarks(Scores, "M", "Mathematics")REAL COURSE DATA · FOLLOW THE PROCEDURE
Call SumMarks with different parameters
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| Call | Returned value |
|---|---|
| SumMarks(Scores,F,Mathematics) | 951 |
| SumMarks(Scores,M,Mathematics) | 1220 |
| SumMarks(Scores,F,Chemistry) | 1064 |
| SumMarks(Scores,M,Chemistry) | 1250 |
Sum starts at zero on every call. Changing parameters does not require rewriting the loop. return Sum sends the computed number to the caller; writing it into GirlsMaths preserves it for later. Equal code does not mean equal answers when the parameters differ.
The groups contain 13 F and 17 M records. Raw sums alone do not establish which group has a higher average. Divide each group sum by its own count for that question.
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Which argument is an attribute name in SumMarks(F,Chemistry)?
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Chemistry. F is the category value to compare.
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What does return Sum do?
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It sends the computed Sum back to the code that called the procedure.
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Should Sum keep its value from the previous call?
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No. Each new sum computation initializes its own Sum to zero.
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Do larger total group marks necessarily mean a larger average?
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No. Groups can have different numbers of records.