Repetition Structure PSUT重复结构的阵发性室上性心动过速课件.ppt

Chapter 6: The Repetition Structure The Repetition Structure (Looping)Lesson A Objectives Code the repetition structure using the For...Next and Do...Loop statements Write pseudocode for the repetition structure Create a flowchart for the repetition structure Initialize and update counters and accumulators The Repetition Structure Use the repetition structure to repeatedly process one or more program instructions until some condition is met, at which time the repetition ends The repetition structure is referred to as a loop The Repetition Structure (continued) Pretest loop: evaluation occurs before the instructions within the loop are processed Posttest loop: evaluation occurs after the instructions within the loop are processed The For…Next Loop Use the For…Next statement to code a loop that repeats for a specific number of times The For…Next Loop (continued) The For…Next Loop (continued) counter is a numeric variable that keeps track of how many times the loop instructions are repeated startvalue, endvalue, and stepvalue Must be numeric Can be positive or negative, integer or non-integer Default stepvalue is 1 The For…Next Loop (continued) The For…Next Loop (continued) The Do…Loop Statement Unlike the For…Next statement, the Do…Loop statement can be used to code both a pretest loop and a posttest loop The Do…Loop statement begins with the Do clause and ends with the Loop clause The Do…Loop Statement (continued) The Do…Loop Statement (continued) The Do…Loop Statement (continued) The Do…Loop Statement (continued) Using Counters and Accumulators Counters and accumulators are used within a repetition structure to calculate subtotals, totals, and averages A counter is a numeric variable used for counting something and is typically updated by 1 An accumulator is a numeric variable used for accumulating and is updated by an amount that varies Using Counters and Accumulators (continued) Initializing: assigning a beginning value to the counter or accumulator Updating (i