An overview of structured forms

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In structured programming theory, only three basic control logic structures are required to program any function:

  • Sequences
  • Selection
  • Iteration.

A sequence is the processing of one function after the other, as shown in Figure 1. No special logic is required because processing is always sequential.

Figure 1. Sequence: Processing Code Sequentially Alternative text description not available.

A selection is the choice between two or more functions to be processed based on a condition.

For example, the IF macro group, shown in Figure 2, is used for selection.

Figure 2. Selection: Using a Condition Alternative text description not available.

The CASE macro group, shown in Figure 3, is another example of a macro group used for selection.

Figure 3. Selection: Using a Case Number Alternative text description not available.

An iteration is the repeated processing of the same code while, or until, a condition is true, as shown in Figure 4.

Figure 4. Simple Iteration: The Difference between DO WHILE and DO UNTIL Alternative text description not available.

Note:
  • The code can be bypassed (never processed) if condition is false on entry to the DO WHILE loop.
  • The code is processed at least once before the DO UNTIL condition is tested.