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within the process being repeated that changes the value of the flag (through an assignment statement). Because the update depends on what the process does, at times we have to design the process before we can decide how to update the condition. |
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Designing the Process Within the Loop |
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Once we've determined the looping structure itself, we can fill in the details of the process. In designing the process, we first must decide what we want a single iteration to do. Assume for a moment that the process is going to execute only once. What tasks must the process perform? |
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What is the process being repeated? |
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To answer this question, we have to take another look at the problem statement. The definition of the problem may require the process to sum up data values or to keep a count of data values that satisfy some test. For example: |
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Count the number of integers in the file howMany. |
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This statement tells us that the process to be repeated is a counting operation. |
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Read a stock price for each business day in a week and compute the average price. |
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In this case, part of the process involves reading a data value. We have to conclude from our knowledge of how an average is computed that the process also involves summing the data values. |
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In addition to counting and summing, another common loop process is reading data, performing a calculation, and writing out the result. Many other operations can appear in looping processes. We've mentioned only the simplest here; we'll look at some other processes later on. |
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After we've determined the operations to be performed if the process is executed only once, we design the parts of the process that are necessary for it to be repeated correctly. We often have to add some steps to take into account the fact that the loop executes more than once. This part of the design typically involves initializing certain variables before the loop and then reinitializing or updating them before each subsequent iteration. |
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How should the process be initialized? |
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How should the process be updated? |
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For example, if the process within a loop requires that several different counts and sums be performed, each must have its own statements to initialize variables, increment counting variables, or add values to sums. Just deal with each counting or summing operation by itselfthat is, first write the initialization statement, and then write the incrementing or summing statement. After you've done this for one operation, you go on to the next. |
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