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Chapter 5: Looping

Chapter 5: Looping. Using the while Loop. Loop A structure that allows repeated execution of a block of statements Loop body A block of statements within a looping structure C# types of loops: while loop for loop do loop (or do...while loop). Using the while Loop (cont’d.).

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Chapter 5: Looping

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  1. Chapter 5: Looping

  2. Using the while Loop • Loop • A structure that allows repeated execution of a block of statements • Loop body • A block of statements within a looping structure • C# types of loops: • while loop • for loop • do loop (or do...while loop) Microsoft Visual C# 2012, Fifth Edition

  3. Using the whileLoop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  4. Using the while Loop (cont’d.) • while loop • Used to execute a body of statements continuously as long as some condition continues to be true • Infinite loop • A loop that never ends • Making a while loop end correctly • Initialize the loop control variable • Test the control variable in the while expression • Alter the value of the control variable in the code block Microsoft Visual C# 2012, Fifth Edition

  5. Using the while Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  6. Using the while Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  7. Using the while Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  8. Using the while Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  9. Using the while Loop (cont’d.) • Empty body • A body with no statements in it • Alter the control variable by: • Incrementing, or adding to it • Decrementing, or subtracting from it • Definite loop or counted loop • A loop for which the number of iterations is predetermined • Indefinite loop • The value of a loop control variable is not altered by arithmetic, but instead is altered by user input Microsoft Visual C# 2012, Fifth Edition

  10. Using the while Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  11. Using the for Loop • for loop • A shorthand way to create definite loops • Sections of the loop • Control variable initialization • Control variable testing • Control variable updating Microsoft Visual C# 2012, Fifth Edition

  12. Using the for Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  13. Using the do Loop • do loop • Checks at the “bottom” of the loop after one repetition has occurred • Convenient when you know you want to perform some task at least one time Microsoft Visual C# 2012, Fifth Edition

  14. Using the do Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  15. Using the do Loop (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  16. Microsoft Visual C# 2012, Fifth Edition

  17. Using Nested Loops • When loops are nested, each pair contains an inner loop and an outer loop • The inner loop must be entirely contained within the outer loop • Loops can never overlap Microsoft Visual C# 2012, Fifth Edition

  18. Using Nested Loops (cont’d.) Microsoft Visual C# 2012, Fifth Edition

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  20. Microsoft Visual C# 2012, Fifth Edition

  21. Accumulating Totals • Totals are accumulated • Gathered together and added into a final sum by processing individual records one at a time in a loop Microsoft Visual C# 2012, Fifth Edition

  22. Accumulating Totals (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  23. Accumulating Totals (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  24. Improving Loop Performance • Make sure the loop does not include unnecessary operations or statements • Example: A loop should execute while x is less than the sum of two integers, a and b • Initial solution while(x < a + b) // loop body • Better solution int sum = a + b; while(x < sum) // loop body Microsoft Visual C# 2012, Fifth Edition

  25. Improving Loop Performance (cont’d.) Microsoft Visual C# 2012, Fifth Edition • Comparing to zero • Making a comparison to 0 is faster than making a comparison to any other value

  26. Improving Loop Performance (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  27. Improving Loop Performance (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  28. Improving Loop Performance (cont’d.) Microsoft Visual C# 2012, Fifth Edition • Using prefix incrementing rather than postfix incrementing • A common operation in forloops

  29. Improving Loop Performance (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  30. Improving Loop Performance (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  31. Looping Issues in GUI Programs • Using a loop within a method in a GUI application is no different from using one in a console application • Event-driven programs sometimes require fewer coded loops • Some events are determined by the user’s actions when the program is running, rather than by the programmer’s coding Microsoft Visual C# 2012, Fifth Edition

  32. Looping Issues in GUI Programs (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  33. Looping Issues in GUI Programs (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  34. Looping Issues in GUI Programs (cont’d.) Microsoft Visual C# 2012, Fifth Edition

  35. Looping Issues in GUI Programs (cont’d.) Microsoft Visual C# 2012, Fifth Edition

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