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Chapter 6

Chapter 6. Loops. A control structure that causes a statement or group of statements to be executed repeatedly There are 3 types of loops while for do while. The While Statement. while (expression) Statement while (inputVal != 25) cin >> inputVal;. while and if.

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Chapter 6

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  1. Chapter 6

  2. Loops • A control structure that causes a statement or group of statements to be executed repeatedly • There are 3 types of loops • while • for • do while

  3. The While Statement while (expression) Statement while (inputVal != 25) cin >> inputVal;

  4. while and if • Not the same construct • If statements do not repeat • While statements will repeat until the expression becomes false • While statements should always have a statement that will eventually make the expression to become false

  5. Phases of Loop Execution • Loop entry – The point at which of the low of control reaches the first statement inside a loop. • Iteration – An individual pass through or repetition of, the body of a loop. • Loop test – The point at which the While expression is evaluated and a decision is made either to begin a new iteration or skip to the statement immediately following the loop. • Loop exit – the point at which the repetition of the loop ends and control passes the first statement following the loop. • Termination condition – The condition that causes the loop to be exited.

  6. Loops using the While Statement • Count-Controlled Loops • Event-Controlled Loops • Sentinel-Controlled Loops • End-of-File Controlled Loops • Flag-Controlled Loops

  7. Count Controlled Loops loopCount = 1; while (loopCount <= 10) { cout << “Hello!\n”; loopCount++; }

  8. Sentinel-Controlled Loops while(!(month == 2&&day == 31)) { cin >> month >> day; … }

  9. Sentinel-Controlled Loops cin >> month >> day; while(!(month == 2&&day == 31)) { cin >> month >> day; … }

  10. Sentinel-Controlled Loops cin >> month >> day; while(!(month == 2&&day == 31)) { … cin >> month >> day; }

  11. End-of-File Controlled Loop cin >> month >> day; while ( cin ) { … cin >> month >> day; }

  12. End-of-File Controlled Loop cin >> month >> day; while ( !cin.eof() ) { … cin >> month >> day; }

  13. Flag-Controlled Loop sum = 0; cin >> number; bool nonNegative = true; while ( nonNegative ) { if ( number > 0) sum = sum + number; else nonNegative = false; cin >> nonNegative; }

  14. Quiz • Write a code fragment that uses a loop to compute the sum of the squares of a series of numbers from 1 to a user entered number. Upon loop exit the sum of the squares should be printed.

  15. Looping Subtasks • Counting • Summing • Keeping track of the previous value

  16. Counting Loop Iteration Counter: A counter variable that is incremented with each iteration of a loop count = 0; cin.get( inChar ); while ( inChar != ‘.’ ) { count++; cin.get( inChar ); }

  17. Summing Loop sum = 0; cin >> number; bool nonNegative = true; while ( nonNegative ) { if ( number > 0) sum = sum + number; else nonNegative = false; cin >> nonNegative; }

  18. Remembering Loop count = 0; in.get ( prevChar ); in.get ( currChar ); while ( !in.eof() ) { if ( currChar == ‘=‘ && prevChar == ‘!’ ) count++; prevChar = currChar; in.get( currChar ); }

  19. Designing Loops • What is the condition that ends the loop? • How should the condition be initialized? • How should the condition be updated? • What is the process being repeated? • How should the process be initialized? • How should the process be updated? • What is the state of the program on exiting the loop?

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