Unit 4 Repetition and Loops

Key Concepts Flowcharting a loop Types of loops Counter-controlled loops while statement Compound assignment operator for statement Sentinel-controlled loops Endfile-controlled loops Nested loops do-while statement Flag-controlled loops Debuggers Diagnostic statements Common errors

Figure 5.1 Flow Diagram of Loop Choice Process

Types of Loops Table 5.1

Counter-Controlled Loops Used when you know the number of times the loop must execute General steps: 1.Set loop control variable to 0 2.While loop control variable < final value Execute statements Increase loop control variable by 1

Figure 5.3 Flowchart for a while Loop

Figure 5.2 Program Fragment with a Loop

Figure 5.4 Program to Compute Company Payroll

Figure 5. Program to Compute Company Payroll (cont’d)

Compound Assignment Operators Table 5.3

Figure 5.5 Using a for Statement in a Counting Loop

for Loop Style Separate lines for each expression for (count_emp = 0; count_emp < number_emp; count_emp += 1 ) {…} All expressions on one line for (i = 0; i < max; i += 1) {…}

Figure 5.6 Comparison of Prefix and Postfix Increments

Figure 5.7 Function to Compute Factorial

Figure 5.8 Displaying a Celsius- to- Fahrenheit Conversion Table

Conditional Loops Execute until a condition is no longer true or becomes true. Example using a while statement: printf("Enter number of values> "); scanf("%d", &num_obs); while (num_obs < 0) { printf("Negative, try again> "); scanf("%d", &num_obs); }

Figure 5.9 Program to Monitor Gasoline Storage Tank

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

Sentinel-Controlled Loop Data value is used to determine end- point. General format 1.Get a line of data 2.While the sentinel value has not been encountered a.Process the data line. b.Get another line of data.

Correct vs. Incorrect Sentinel Loop Correct 1.Initialize sum to 0 2.Get first score 3.while score is not the sentinel a.Add score to sum b.Get next score Incorrect 1.Initialize sum to 0 2.while score is not the sentinel a.Get score b.Add score to sum

Figure 5.10 Sentinel-Controlled while Loop

Sentinel Loop with a for Statement /* Accumulate sum of all scores. printf(“Enter first score (or %d to quit)> “, SENTINEL); for(scanf(“%d”, &score); score != SENTNEL; scanf(“%d”, &score)) { sum += score; printf(“Enter next score (%d to quit)> ”, SENTINEL);

Endfile-Controlled Loops Used to read a file into memory. Loop until EOF. General format: 1.Get the first data value and save input status. 2.While input status does not indicate that end of file has been reached. a.Process data value. b.Get next data value and save input status.

Figure 5.11 Batch Version of Sum of Exam Scores Program

Figure 5.12 Program to Process Bald Eagle Sightings for a Year

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

Figure 5.13 Nested Counting Loop Program

do-while Statement Example 5.9 do { printf(“Enter a letter from A through E> “); scanf(“%c”, &letter_choice); } while (letter_choice ‘E’);

Flag-Controlled Loops Declare a flag variable of type int. Initialize the flag to a value that is not the exit condition. Loop on the flag becoming true or false. Set the flag within the loop to indicate exit condition.

Figure 5.14 Validating Input Using do-while Statement

Figure 5.15 Structure Chart for Computing Solar Collecting Area Size

Figure 5.16 Program to Approximate Solar Collecting Area Size

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

Debugger Debugger allows: – Single-step execution – Setting breakpoints on a statement – Variable inspections

Diagnostic Calls Use printf to output intermediate results. Define a constant named DEBUG and use a conditional: #define DEBUG 1 if (DEBUG) printf("*** score is %d, sum is %d\n", score, sum);

Off by One Errors This loop executes n+1 times: for (count = 0; count <= n; ++count) sum += count; Always test at the loop boundaries to verify the loop does the right thing.

Common Errors Forgetting to use curly braces around multiple steps Termination condition never met (infinite loop) Mistyping an equality operator (==) as an assignment operator (=) Confusing do-while and while Mistakes related to operator precedence – Avoid increment, decrement, and compound assignment operators in complex expressions. – Use parentheses to control evaluation order.