MSAS5104 Programming with Data Structures and Algorithms

1. MSAS5104Programming with Data Structures and Algorithms Week 6 Scott Marino Scott Marino MSMIS Kean University

2. Iteration Pretest loops Post test loops Counter controlled loops Nested loops Lab 6 and 7 / Homework Topics Scott Marino MSMIS Kean University

3. Iteration • A computer is good for handling repetitive tasks • The process of repeating a set of sequence instructions is known as an iteration sequence or a loop • Each loop requires a test/condition for exiting the loop, else it will run forever • Each iteration of a loop is commonly referred to as a cycle Scott Marino MSMIS Kean University

4. Iteration • The exit test for a loop can come at the beginning or end of the looping cycle • Pretest or top-tested loops have the exit test before the loop cycle starts • Top tested loops may never execute if the exit condition is present before the loop starts • Posttest or bottom-tested loops have the exit test at the end of the loop cycle • Bottom tested loops will always execute at least one time since the test is at the end of the cycle Scott Marino MSMIS Kean University

5. Iteration • From the payroll example: • Gather time card datawhile more employees compute payrollend-while • Gather time card datado compute payrollwhile more employees Scott Marino MSMIS Kean University

6. Pretest Loops • Syntax: • while (condition) statement; • while (condition) {statement(s);} • This top-tested looping code will execute the statements as long as the condition evaluates to true Scott Marino MSMIS Kean University

7. Posttest Loops • Syntax: • do statement; while (condition); • do {statement(s); } while (condition); • This bottom-tested looping code will always execute at least one cycle • All loops should have some change of the variable in the condition to allow exit from the loop Scott Marino MSMIS Kean University

8. Sentinel Values • A sentinel value is an expected value, usually entered via the keyboard, used to exit a loop • It is always a value that would not occur during the normal course of processing • A sentinel value controlled loop is a common programming construct Scott Marino MSMIS Kean University

9. Counter Controlled Loops • There are instances where a loop would need to be executed a specific number of times • Usually done when the number of input or output items is known • Elements in an array • Characters in a string • Lines on a report • Underscores or asterisks on a report • Using a counter controlled loop, a set of sequence instructions is executed n times Scott Marino MSMIS Kean University

10. Counter Controlled Loops • The following elements are required for a counter controlled loop • Initialization - to start the counter with a specified value • Test - to exit the loop when the number of iterations is complete • Body - the sequence instructions • Counter - the count of the number of cycles • End - denotes the end of the cycle Scott Marino MSMIS Kean University

11. Counter Controlled Loops • loopctr = 0;while (loopctr < 4) { cout << loopctr << “\n”; loopctr++;} • Will execute the loop four times • What will the value of loopctr be after the loop is exited? Scott Marino MSMIS Kean University

12. Counter Controlled Loops - FOR • for (initialization; test; counter) statement; • for (initialization; test; counter) {statement(s);} // end for • The for loop is a specific construct to handle counter based looping • “FOR” loops have a top tested condition Scott Marino MSMIS Kean University

13. Counter Controlled Loops - FOR • for (loopctr = 0; loopctr < 4; loopctr++) { cout << loopctr << “\n”;} • Will execute the loop cycle four times • Cleaner coding than the while loop with “manual” counter incrementing • What will it print? Scott Marino MSMIS Kean University

14. Nested Looping • There are instances where a loop inside a loop needs to be executed • The loops are typically called inner and outer loops • For each iteration of the outer loop, a complete cycle of the inner loop is performed Scott Marino MSMIS Kean University

15. Nested Looping • for (outerctr = 1; outerctr <= 5; outerctr++) { for (innerctr = 1; innerctr <= 10; innerctr++) { cout << “*”; } // end inner loop cout << “\n”;} // end outer loop • Will print a block of asterisks 10 columns wide by 5 lines • The new line character is executed as part of the outer loop Scott Marino MSMIS Kean University

16. Homework / Lab 6 • Enhance the Celsius / Fahrenheit conversion program • Add a loop to continue execution until the user requests an exit • Add an exit value to the prompt that asks for the conversion of F -> C or C -> F to include an exit value Scott Marino MSMIS Kean University

17. Homework / Lab 7 • Write a program the prints the multiplication (times) table up to 10x • 1 2 3 41 1 2 3 42 2 4 6 83 3 6 9 124 4 8 12 16 • Hints: • Use the setw() operator to control the spacing • A nested loop is required to produce the output Scott Marino MSMIS Kean University