Chapter 7 The Repetition Structure Introduction to Programming

Chapter 7: The Repetition Structure Introduction to Programming with C++ Fourth Edition Introduction to Programming with C++, Fourth Edition

Objectives • Include a repetition structure in pseudocode and in a flowchart • Code a pretest loop using the C++ while statement • Initialize and update counters and accumulators • Code a pretest loop using the C++ for statement Introduction to Programming with C++, Fourth Edition 2

Using the Repetition Structure • Repetition structure or loop - allows repeated processing of one or more program instructions until some condition is met • Repetition structure can be either a pretest loop or a posttest loop – Pretest loop: evaluation occurs before loop instructions are processed – Posttest loop: evaluation occurs after loop instructions are processed Introduction to Programming with C++, Fourth Edition 3

Pretest Loops Introduction to Programming with C++, Fourth Edition 4

Pretest Loops (continued) Introduction to Programming with C++, Fourth Edition 5

Pretest Loops (continued) • Every loop has: – a loop condition – a loop body • Loop body: – instructions within a loop • Loop condition: – appears at the beginning of a pretest loop – determines the number of times instructions within the loop are processed Introduction to Programming with C++, Fourth Edition 6

Pretest Loops (continued) • Sentinel value – special value to end the loop • Priming read: – Appears above the loop – Used to prepare or set up the loop Introduction to Programming with C++, Fourth Edition 7

Components of a Loop Introduction to Programming with C++, Fourth Edition 8

O’Donnell Incorporated Algorithm Shown in Flowchart Form Introduction to Programming with C++, Fourth Edition 9

Using the while Statement to Code the Pretest Loop • While statement: programmer must supply the loop condition to be evaluated • Loop condition: – must be a Boolean expression (true or false) – can contain variables, constants, functions, methods, arithmetic operators, comparison operators, and logical operators • Endless or infinite loop – one that processes its instructions indefinitely Introduction to Programming with C++, Fourth Edition 10

Syntax of the C++ while Statement Introduction to Programming with C++, Fourth Edition 11

Using Counters and Accumulators • Counter - a numeric variable used for counting • Accumulator - a numeric variable used for accumulating a value • Initializing - assigning a beginning value to the counter or accumulator • Updating or incrementing - adding a number to the value stored in the counter or the accumulator Introduction to Programming with C++, Fourth Edition 12

Counter-Controlled Pretest Loops Introduction to Programming with C++, Fourth Edition 13

Using the for Statement to Code a Pretest Loop • Most common use for the for statement: – Code pretest loops whose processing is controlled by a counter • For statement: – Begins with the for clause – Followed by the body of the loop • If the loop body contains more than one statement: – Statements must be entered as a statement block i. e. , enclosed in braces ({}) Introduction to Programming with C++, Fourth Edition 14

Syntax of the C++ for statement Introduction to Programming with C++, Fourth Edition 15

for Statement Displays the Numbers 1 Through 3 Introduction to Programming with C++, Fourth Edition 16

for Statement Calculates and Displays a Commission Introduction to Programming with C++, Fourth Edition 17

for Statement Calculates and Displays a Bonus Introduction to Programming with C++, Fourth Edition 18

Summary • Repetition structure or loop - allows repeated processing of one or more program instructions until some condition is met – Repetition structures contain a condition and a loop body Introduction to Programming with C++, Fourth Edition 19