Mastering While Loops in C++ Programming

1. GAME102 - IntroWHILE LOOPS G. MacKay

2. Fundamental Control Structures • STRAIGHT LINE • CONDITIONAL • LOOPS

3. What is LOOP? • Logic that repeats itself • Usually verbally identified by “while” or “until”

4. In human terms? • while (the light is red) waitwhile the meat is raw cook

5. Flowchart of a WHILE LOOP • NoteONE ENTRANCEONE EXITfrom structure

6. C++ Code of a WHILE LOOP • As followswhile (test) statement;

7. C++ Code for Counter • As followscount = 1;while (count<=10){cout << count<<endl; count = count +1;}

8. C++ Code for Counter • As followscount = 1;while (count<=10){cout << count<<endl; count = count +1;} • NOTE:initialize count BEFORE LOOP • INCREMENT count INSIDE loop • TEST FOR COUNT

9. C++ Code for Counter • As followscount = 1;while (count<=10){cout << count<<endl; count = count +1;} LOOP RULE • Test should make progress towards completion WATCH FOR • Incorrect test direction • No increment

10. C++ Code for Counter – ++ • As followscount = 1;while (count<=10){cout << count<<endl; count ++;} Operator ++ Means add one to the variablecount = count + 1;count ++;// SAME!!!

11. C++ Code for Counter - PROBLEM • As followscount = 1;while (count<=10)cout << count<<endl; count = count +1; What happens? • There are no braces, so ONE statement goes with the whileIncrement is OUTSIDE the while • INFINITE LOOP!!!!!

12. C++ Code for Counter - PROBLEM • As followscount = 1;while (count>=10){cout << count<<endl; count = count +1;} What happens? • The test direction is incorrect • When count=1, test is FALSE so the loop is not entered!!!

13. C++ Code for Counter – by twos • As followscount = 1;while (count<=10){cout << count<<endl; count = count +2;} What happens? • When count=1, test is TRUE so the loop is entered. • Display 1 • Count becomes 3… and Display 3 • Then.. 5, 7, 9 • EXIT… (on 11)

14. C++ Code for Counter – by twos • As followscount = 1;while (count<=10){cout << count<<endl; count += 2;} Operator += Means add whatever is on the right side to whatever is on the left sidecount = count + 2;count += 2;// SAME!!!

15. PROBLEM using loops • Add 10 numberstogether and display the sum

16. Requirements? • Read 10 numbers • Add the numbers • Display sum

17. Design • Flowchart

18. Design • Pseudo-code Prompt user Set count to 1 Set sum to 0 While count <=10 Read number Add number to sum Add to 1 to count Display sum

19. CODING #include <iostream> using namespace std; int main() { int number; int sum; int count; cout << "Enter 10 integer numbers: "; count = 1; sum = 0; while ( count <= 10) { cin >> number; sum += number; count++; } cout << "Sum is " << sum << endl; return 0; }

20. Testing your code? • Identify the limits of your code • Maximum number of reads • Minimum number of reads • Illegal reads • High values entered • Low values entered • Test NORMAL case ANDlimits

21. Testing your code? • In large projects, test groups actually plan tests around the REQUIREMENTS of the project

22. Testing does not work? • LOGIC ERROR • Check that code matches design • FIX code • Check the design is correct • FIX design

23. The OTHER loop….. • do{ statement1; statement2;} while(test);

24. DO…WHILE Design Difference • PROCESS BLOCK is ALWAYS PERFORMED AT LEAST ONCE

25. DO…WHILE Design Usage • Do you want to play again?MAJOR USAGE

26. DO…WHILE Design Usage • Studies have shown that 90% of all programming loops are WHILE type rather than DO…WHILE • Use DO…WHILE only when it makes sense