Chapter 5: Repetition and Loop Statements By: Suraya Alias

5.1 Repetitions in Program Loop –a control structure that repeats a group of steps in a program 3 loop control statements  While, for, do-while Loop body contains the statements to be repeated

Figure 5.1 Flow Diagram of Loop Choice Process 1-3

1-4 Loop types 1) Counting loopCan be determines before loop execution, exactly how many loop repetition will be needed to solve the problem While for 2) sentinel- controlled loop Input of a list of data of any length ended by a special value While, for 3) endfile- controlled loop Input of a single list of data of any length from a a data file While, for 4) Input validation loop Repeated interactive input of data value until a a value within the valid range is entered do-while 5) General conditional loop Repeated processing of data until a desired condition is met While, for

5.2 Counting loops and the while statement Counter-controlled loop (counting loop) is a loop whose required number of iterations can be determined before loop execution begins Format Set loop control variable = 0 While loop control variable < final value Increase loop control variable by 1

The While Statement while (count_emp < 7)  (count_emp < 7) is the loop repetition condition, a condition which control the loop repetition  The loop is repeated when the condition is true, the loop exited when false  count_emp is the loop control variable because it determines whether the loop body is repeated.  The loop control variable must be; Initialized, count_emp = 0 Tested, count_emp is tested before the start of each loop repetition Updated, count_emp is updated (value increased by 1) during each iteration

Syntax of while statement Syntax : while (loop repetition condition) Statement Example - /* display N star*/ count_star = 0; while (count_star < N) { printf(“*”); count_star = count_star + 1; }

Figure 5.2 Program Fragment with a Loop 1-8

Figure 5.3 Flowchart for a while Loop 1-9

5.3 Computing a Sum or a product in a Loop Accumulator – a variable used to store a value being computed in increments during the execution of a loop total_pay = total_pay + pay; /* add next pay*/ The value of total_pay increases with each loop iteration. To write general loops, the loop repetition condition can be manipulated  count_emp < number_emp  The number of employees must be scanned into variable number_emp before the while statement executes.  We also can use loop to compute the product of a list product = product * item;

Figure 5.4 Program to Compute Company Payroll 1- 11

Figure 5.4 Program to Compute Company Payroll (cont’d) 1- 12

Compound Assignment Operators Statement with simple assignment operator Equivalent statement with compound assignment operator count_emp = count_emp + 1;Count_emp +=1; time = time – 1;time -= 1; total_time = total_time + timetotal_time += time product = product * item;product *= item; n = n * (x + 1);n *= (x + 1);

5.4 The For Statement A for statement has 3 loop control component that is initialization, testing and update in one place. for (count_emp = 0; /*initialization*/ count_emp < number_emp; /*loop repetition condition*/ Count_emp +=1) /*update*/ Syntax : for (initialization expression; Loop repetition condition; Update expression) statement

Figure 5.5 Using a for Statement in a Counting Loop 1- 15

Increment and decrement operators for (counter = 0; counter < limit; ++counter) The side effect of applying the ++ operator is that the value of its operand is incremented by one. The value of the expression in which the ++ is used depends on the position of the operator  Prefix increment : j = ++i The value of the expression is the variables value after incrementing  Postfix increment : j = i++ The value of the expression is the variables value before incrementing

Figure 5.6 Comparison of Prefix and Postfix Increments 1- 17

Figure 5.7 Function to Compute Factorial 1- 18

Figure 5.8 Displaying a Celsius-to-Fahrenheit Conversion Table 1- 19

5.5 Conditional Loops Is used to control the number of time the loop executes/repeats. Such as continue prompting the user for data as long as the response is unreasonable. The loop can be process in a function subprogram, it simplifies the main function.

Figure 5.9 Program to Monitor Gasoline Storage Tank 1- 21

Figure 5.9 Program to Monitor Gasoline Storage Tank (cont’d) 1- 22

Figure 5.9 Program to Monitor Gasoline Storage Tank (cont’d) 1- 23

5.6 Loop design Sentinel-Controlled Loops  Sentinel value is an end marker that follows the last item in a list of data  Sentinel loop 1. Initialize sum to zero 2. Get first score 3. While score is not the sentinel 1. Add score to sum 2. Get next score

Figure 5.10 Sentinel-Controlled while Loop 1- 25

Sentinel Loop using For printf(“enter first score(or %d to quit) >”, sentinel); for (scanf(“%d”, &score); score !=sentinel; scanf(“%d”, &score)) { sum += score; printf(“Enter next score (%d to quit)>”,sentinel); }

Endfile-Controlled Loop & Infinite loops on faulty data Figure 5.11 Batch Version of Sum of Exam Scores Program Figure 5.11 Batch Version of Sum of Exam Scores Program 1- 27

5.7 Nested loops Figure 5.12 Program to Process Bald Eagle Sightings for a Year Figure 5.12 Program to Process Bald Eagle Sightings for a Year 1- 28

Figure 5.12 Program to Process Bald Eagle Sightings for a Year (cont’d) 1- 29

5.8 the do-while statement and Flag-Controlled Loops Syntax : do Statement while (loop repetition condition); Example : Do Status = scanf(“%d”,num); While (status > 0 && (num % 2) !=0); Flag = is a type int variable used to represent whether or not a certain event has occurred. The flag has the value of true(1) and false(0);

Figure 5.13 Nested Counting Loop Program 1- 31

Figure 5.14 Validating Input Using do-while Statement 1- 32

Figure 5.15 Structure Chart for Computing Solar Collecting Area Size 1- 33

Figure 5.16 Program to Approximate Solar Collecting Area Size 1- 34

Figure 5.16 Program to Approximate Solar Collecting Area Size (cont’d) 1- 35

Figure 5.16 Program to Approximate Solar Collecting Area Size (cont’d) 1- 36

Figure 5.16 Program to Approximate Solar Collecting Area Size (cont’d) 1- 37

5.10 How to debug and test Programs Using debugger programs  Using Single step execution or breakpoints Debugging without a debugger  Using printf or diagnostic call Loop boundaries = initial and final values of the loop control variable Test by running program using multiple test data

New C construct Counting for loop For (num=0; num < 26; ++num) { Square = num * num; Printf(“%5d %5d\n”, num, square); } Counting for loop with negative steps For (volts=20; volts>=-20; volts -=10) { current = volts/resistance; printf(“%5d %8.3f\n”, volts, current); } Sentinel controlled while loop product = 1; printf(“Enter %d to quit\n”, senval); printf(“Enter first number”); scanf(“%d, &dat”); while (dat != senval) { product *=dat; printf(“next number”); scanf(“%d”, &dat);} Endfile controlled while loop sum=0; status = fscanf(infil, “%d”, &n); while (status ==1){ sum += n; status = fscanf(infil, “%d”, &n); }

New C construct do-while loop do { Printf(“positive number < 10”); sacnf(“%d”, &num); } while (num = 10); Increment/ decrement Z= ++j * k--; Compound Assignment Ans *= a – b;