1. Loops A loop is a repetition control structure.
body - statements to be repeated
control statement - decides whether another repetition needs to be made
leading decision loop - control statement before body
trailing decision loop - control statement after body
Counted loop- for
Logical loop – while or do..while

2. Leading Decision prime the loop //START while (condition) //TEST {
body of loop – //ACTION
group of one or more statements
indent one level
//RESTART }
loops

3. When the expression is tested and found to be false, the loop is exited and control passes to the statement which follows the loop body.
while LOOP
FALSE
Expression
TRUE
body
statement

4. 1-2-3-4 for While Loops Initial condition //START TEST - while(…)
ACTION (steps needed to solve the problem)
RESTART (often the same as step 1)
loops

5. Example cout <<"Do you want to play?(y/n)"; //START
cin >> ans;
while ((ans == 'y') || (ans == 'Y'))// TEST {
… //body // ACTION
cout <<"Do you want to continue(y/n)?";//RESTART }
cout <<"Thanks for playing! " << endl;
loops

6. Loops Sentinel controlled
keep processing data until a special value is entered to indicate that processing should stop
Read blood pressures until a special value
(like -1) selected by you is read.
Count Controlled
keep processing data for a specified number of times
Read 100 blood pressures.
End-of-file Controlled
keep processing data as long as there is more data in the file
Read all the blood pressures from a file no matter how many are there
Flag Controlled
keep processing data while a flag condition is true
Read blood pressures until a dangerously high BP (200 or more) is read.
loops

7. A Sentinel-controlled Loop
Read numbers until -1, 999
Not always easy to determine sentinel value
requires a "priming read"
"priming read" means you read one set of data before the while

8. 1-2-3-4 Sentinel Value Initial condition (START) TEST - while(…)
Get first value
TEST - while(…)
while (val != sentinel)
ACTION
RESTART- often the same as step 1
Get next value
loops

9. // Sentinel controlled loop
total = 0;
cout << "Enter the price of the item (-1 to stop ) ";//START
cin >> itemPrice;
while (itemPrice > 0) // while not sentinel TEST {
total = total + itemPrice; // ACTION
cout <<"Enter item price(-1 to stop ) "; // RESTART }
cout << total;

10. Example cin >> number; while (number < 0) {
cout << "Enter positive values only! "; }
loops

11. Reading from a file first open file (later)
infile points to file (can be any name)
infile >> fahrTemp; 1
infile >> cityName >> fahrTemp;
loops

12. Reading from a file with a sentinel value
infile >> fahrTemp; //read from a file start
while (fahrTemp != 999) //test {
celsTemp = (5 * (fahrTemp – 32))/9 ; //action
cout << fahrTemp << celsTemp;
infile >>fahrTemp; //restart }
loops

13. End-of-File Controlled Loop
depends on fact that a file goes into fail state when you try to read a data value beyond the end of the file
No trailer record
while (there is a record)
while (not end of file)
while (infile) // this is c
Computer indicates there are no more records by sending a signal to the program
Must read record before entering loop – there may be no records

14. 1-2-3-4 Reading from file START : Read first record
TEST- while (infile)
ACTIONS
RESTART - Read next record- often the same as step 1
loops

15. Example infile >> fahrTemp; //start while (infile) //test {
celsTemp = (5 * (fahrTemp – 32))/9;//actions
cout << fahrTemp <<celsTemp;
infile >> fahrTemp ; //restart }
loops

16. // End-of-file controlled loop
//Open file
total = 0;
infile >> thisBP; // priming read Start
while (infile) //test {
total = total + thisBP; //action
infile >> thisBP; // read another - restart loop }
cout << total;

17. Do something a set number of times Need counter
Count-controlled loop
Do something a set number of times
Need counter
initialize
increment
iteration counter - incremented during each iteration of the loop
event counter - incremented each time a particular event occurs

18. 1-2-3-4 Count Start: Initialize counter
Test - while (counter < limit)
Actions
Restart: Increment counter
loops

19. Known Count //Print Hello 10 times int count ; count = 0; //start
while (count < 10) //test {
cout << "Hello "; //action count = count + 1; //restart }

20. variable count //Print Hello 10 times int count ;
cout << "How many times should we print Hello?"
cin >> count;
while (count > 0) {
cout << "Hello "; 3
count = count -1 ; 4 }

21. Accumulators and Counters
To find the average of a group of numbers-need running total and how many numbers
Counter – storage area in which we count
Initialize: count = 0;
Increment:
count = count + 1 or count++
Accumulator – storage area for keeping cumulative or running totals
Initialize: total = 0;
Update:
total = total + number
total_wages_paid = total_wages_paid + net_pay
loops

22. Counter:
initialize : count = 0;
increment : count++;

23. Sentinel-Controlled While Loop
Adding a Counter to a
Sentinel-Controlled While Loop
int count;
count = 0; // initialize
cin >> item;
while (item != sentinel) {
count++; // increment
Process(item); }

24. Accumulator:
Initialize: total = 0;
Update: total = total + num;

25. Adding a Running Total to a Sentinel-Controlled While Loop
cin >> item;
while (item != Sentinel) {
total = total + item; }

26. int thisBP, total, count ; //Open file count = 0; // initialize 1
infile >>thisBP ;
while ( count < 100 && infile) {
total = total + thisBP ;
count= count + 1
infile >> thisBP; 4 }
cout << "The total = " << total << endl;
if (count != 0)
cout << "The average is " << (float)total/count ; 26

27. Infinite Loop index = 1; while (index < 5)
cout << "Good Morning!“ << endl;
loops

28. Never executed while (ans == "yes" ) { ….
cout << “Add another number? ";
cin >> answer; }
loops

29. Don't forget to prime the loop!
Initialize initial condition by reading in or setting value
cin >> ans
while (ans == 'y')
index = 0
while (index < 10)
infile >> name >> ssNum >>phone; //read record
while (infile)
loops

30. cout << "No numbers entered“ << endl; else
int count;
float total, avg, num;
total = 0;
count = 0;
infile >> num;
while (infile) {
total = total + num;
count = count + 1; }
if (count == 0)
cout << "No numbers entered“ << endl;
else
avg = total/count;
cout << "The average is “ << avg << endl;
loops

31. Flag Controlled Loop countGoodReadings = 0;
isDangerous = false; // initialize Boolean flag
while (!isDangerous)                                              //test {
     cin >> thisBP;                                                  //action
     if ( thisBP >= 200 )
          isDangerous = true; // change flag value
else
          countGoodReadings++; }
cout << countGoodReadings << endl;

32. Trailing Decision Loopdo {
Body
} while (condition);
Test at the bottom
Statements are executed at least once
loops

33. Trailing decision loop
Body
condition
TRUE
FALSE
loops

34. Example do { cout << "Enter two numbers“;
cin >> num1 >>num2;
cout <<num1 << " + " << num2
<< " = " << num1+num2 << endl;
cout << "Do you want to enter two numbers again? ";
cin >> ans;
} while (ans == "yes" );
loops

35. do {
DisplayMenu();
cin >> choice;
switch (choice)
case 1:
PlayBeginner();
break;
case 2:
PlayAdvBeginner();
break
case 3:
PlayIntermediate();
case 4:
default:
cout << “ Invalid option” << endl; }
} while (choice != 4);

36. Counted loop Fixed number of iterations
Use a variable as a counter which starts at a specified number and increments the variable each time the loop is processed
Repeats until the counter is greater than an ending number
Beginning value, ending value, increment value
loops

37. Counted Loop 1 2 4 for (initial step; cond; expression) body (3)
for (initial step; cond; expression)
body (3)
Automatic:
initial step: counter = initVal
Check cond: counter < finalVal
3. If true execute body, else exit
4. Expression: counter++
Back to 2
loops

38. Examples for (count = 1; count <= 10; count++)
cout <<"Hello“ << endl;
cout << count << endl;
for (num = 10; num > 0; num--)
cout >>num
cout << "Blast off“ << endl;
loops

39. Nested Loops
placing of one loop inside the body of another loop is called nesting.
When you "nest" two loops, the outer loop takes control of the number of complete repetitions of the inner loop.  
All types of loops may be nested, the most commonly nested loops are for loops.
When working with nested loops, the outer loop changes only after the inner loop is completely finished

40. NESTED LOOPS

41. Exercises:
Show screen output: for (outer = 0; outer < 2; outer++) {      for (inner = 0; inner <=2; inner++)     {         cout<< outer<< '\t' << inner << '\n';      } }
Show screen output: for (outer = 0; outer < 3; outer++) {      for(inner = 2; inner <=4; inner++)     {           cout<< inner << ' ';      }      cout<< '\n'; }

42. 3. The following set of nested loops is NOT working
3. The following set of nested loops is NOT working. Can you find what is wrong?? for (ctr1 = 1; ctr1 <=10; ctr1++); {       for(ctr2 = 1; ctr2 <=5; ctr2++)      {            number = ctr1 * ctr2;            cout<< number << '\n';      } }
  4.  Show the output for the following program fragment: for (ctr1 = 8; ctr1 > 5; ctr1--) {      for(ctr2 = 1; ctr2 < 3; ctr2++)      {            cout<<ctr1<<" "<<ctr2<<" ";       }       cout<<"\n"; }
5.  Show the output: for(j=0; j<=5; j++) {      for(k=1; k<=j; k++)      {           cout<<"&";      }      cout<<"\n"; } 

43. 6.  Write a program using nested loops to produce the following design:
     *      **      ***      ****      *****      ******
7.  Write a program using nested loops to produce the following design:
     A      AB      ABC      ABCD      ABCDE      ABCDEF 
  8.  Write a program using nested loops to produce a rectangle of *'s with 6 rows and  20 *'s per row.