CHAPTER 4 REPETITION CONTROL STRUCTURE CSC 126Fundamental of

CHAPTER 4: REPETITION CONTROL STRUCTURE CSC 126|Fundamental of Algorithms & Computer Problem Solving

TABLE OF CONTENT • Introduction • Requirement of repetition structure • while statement • Basic iterative problems • for statement • Nested loops

INTRODUCTION

INTRODUCTION • It is used when a statement or a block of statements need to be executed several times. • Programmers use the repetition structures, referred to more simply as a loop, when they need the computer to repeatedly process one or more program instructions until some condition is met, at which time the repetition structures end. • Repetition is also known as iteration or loop. Write I LOVE YOU 100 times

ITERATION CONTROL STRUCTURE Write an algorithm that will ask user to input 5 numbers, then calculate the average of it. Output the average value. Start initialize sum with 0 display “Enter 5 number : “ read no 1, no 2, no 3, no 4, no 5 sum = no 1+no 2+no 3+no 4+no 5 average = sum / 5 display “The total is“, average End What will happen if the algorithm need the user to repeat inserting more then 5 numbers? 10 numbers ? 100 numbers? 1000 numbers?

REQUIREMENT OF REPETITION STRUCTURE • Execution of the loop body is controlled by 3 operation: • Initialization • Evaluation/ condition/ end value • Update

REQUIREMENT OF REPETITION STRUCTURE: INITIALIZATION • Process of assigning value to a loop control variable. • Example of statement: counter = 0 number = 2 Loop Control Variable (LCV)

REQUIREMENT OF REPETITION STRUCTURE: EVALUATION/ CONDITION/ END VALUE • It controls the number of times the statement or the block of statements is being executed. • Examples: counter <=10 status != ‘N’ number != 999

REQUIREMENT OF REPETITION STRUCTURE: UPDATE • Is done by adding/ subtracting a constant, such as 1 or 2, to the value of a variable. • Examples: counter = counter + 1 counter ++ counter = counter - 1 counter -- number = number – 2

REQUIREMENT OF REPETITION STRUCTURE Pseudocode Depend on type of loop structure use (while or for) Initialize LCV Begin counter = 1 Repeat (counter <= 5) output “I love C++” counter ++ End evaluate LCV update LCV Variable counter is known as LCV

REQUIREMENT OF REPETITION STRUCTURE Flow Chart Loop body Start Initialize LCV Counter = 1 Counter <= 5 F Evaluate LCV (loop condition) T I love C++ Counter ++ End Update LCV

while LOOP • The pseudocode for while…end. While statement for loop: Initial value of a loop (initialization) while (condition) statement(s) to be repeated statement to update the condition (update statement) end. While

while LOOP • The flowchart for while…end. While statement for loop:

while LOOP • There are two types of repetition can be implemented. • Counter Loop • where the number of repetition is identified • Sentinel Loop • Where the number of repetition is unknown The while loop can be used to implement both type of repetition control structure.

WHILE LOOP (COUNTER CONTROL)

while LOOP • General syntax: LCV = initial_value; //initialize the LCV while(LCV <= final_value)//expression test the LCV { statement_to_be_executed; : LCV = LCV + step; //update the LCV }

while LOOP LCV = initial_value; while(LCV <= final_value) { statement_to_be_executed; : LCV = LCV + step; } • Loop condition acts as a decision maker and is usually a logical expression. • A Boolean expression that controls the execution of the body of the loop • statement executes if the condition initially evaluates to true • loop condition is then reevaluated • statement continues to execute until the condition is no longer true

while LOOP • Consider: int count = 0; //initialize the LCV while (count < 3) //test the LCV { cout << “Hi” << endl; //Loop Body count = count + 1; //Update LCV } • Loop body executes how many times? count = 0 count < 3 Output count (count = count + 1) 0 0 < 3 (T) Hi 1 1 < 3 (T) Hi 2 2 < 3 (T) Hi 3 3 < 3 (F) exit So, loop body executes 3 times

EXERCISES MAR 2017

BASIC ITERATIVE PROBLEMS • Summation • Average • Counting • Minimum • Maximum

SUMMATION • Calculate sum or total: Task: To calculate total of 5 numbers total = 0; i = 1; while(i <= 5){ cin>>number; total = total + number; i++; } cout<<“ The total is : ”<<total; • Accumulator – to find totals. sum = sum + variable • Is done by adding a variable to another variable. *Accumulator

SUMMATION total = 0; i = 1; while(i <= 5){ cin>>number; total = total + number; i++; } cout<<“ The total is : ”<<total; Sample data: 10 5 4 6 8 Produce tracing table for the above sample data total = 0 i=1 i<=5 cin>>number total=total+number i++ 0 1 T 10 10=0+10 2 T 5 15=10+5 3 T 4 19=15+4 4 T 6 25=19+6 5 T 8 33=25+8 6 F - - - cout<<total 33

SUMMATION - EXERCISE APR 2009

AVERAGE • Calculate average: Task: To calculate average of 5 numbers total = 0; average = 0; i = 1; while(i <= 5){ cin>>number; total = total + number; i++; } average = total/i; cout<<“ The average is : ”<<average;

AVERAGE total = 0; average = 0; i = 1; while(i <= 5){ cin>>number; total = total + number; i++; } Sample data: 10 25 4 6 30 Produce tracing table for the above sample data average = total/(i-1); cout<<“ The average is : ”<<average; Depends on how u initialize your LCV total = 0 i=1 i<=5 cin>>number total=total+number i++ average=total /(i-1) cout<<avera ge

AVERAGE – EXERCISE APR 2009

MAXIMUM • To find maximum value: Task: To find maximum value of 5 numbers *count start at 2 because first number had been entered before the loop Style 1 cin>>number; max = number; i=2 while( i <= 5) { cin>>number; if(number>max) max = number; i++; } cout<<“ The maximum value is : ”<<max; Assume -1 is the maximum value Style 2 max = -1; i=1 while( i <= 5) { cin>>number; if(number>max) max = number; i++; } cout<<“ The maximum value is : ”<<max;

MAXIMUM cin>>number; max = number; i=2 while( i <= 5) { cin>>number; if(number>max) max = number; i++; } cout<<“ The maximum value is : ”<<max; Sample data: 10 50 4 6 30 Produce tracing table for the above sample data

MAXIMUM max = -1; i=1 while( i <= 5) { cin>>number; if(number>max) max = number; i++; } cout<<“ The maximum value is : ”<<max; Sample data: 25 4 6 30 10 Produce tracing table for the above sample data

MINIMUM • To find minimum value: Task: To find minimum value of 5 numbers *count start at 2 because first number had been entered before the loop cin>>number; min = number; i = 2; while( i <= 5) { cin>>number; if(number<min) min = number; i++; } cout<<“ The minimum value is : ”<<min; Assume current minimum value 1000 min = 1000; i = 1; while( i <= 5) { cin>>number; if(number<min) min = number; i++; } cout<<“ The minimum value is : ”<<min;

MINIMUM - EXERCISE OCT 2012

COUNTING • Count Task: user requires to input 5 numbers. Calculate and entered. display how many even numbers in a group of 5 numbers *counter used to count amount of even number count. E = 0; i=1 while( i <= 5) { cin>>number; if(number%2==0) count. E= count. E + 1; i++; } cout<<“ The amount of even numbers are : ”<<count. E;

COUNTING - EXERCISE • Write a complete C++ program to allow user to input 10 numbers using while loop. Count and display how many numbers that can be divisible by 3 and by 5.

WHILE LOOP – SENTINEL CONTROL

WHILE LOOP • A sentinel-controlled while loop uses a special value called sentinel to control the loop. • Sentinel value is a special value that indicates the end of a set of data or of a process • Sentinel variable is tested in the condition and loop ends when sentinel is encountered

WHILE LOOP • General syntax:

• Example #include <iostream> #include <conio> int main() { char answer; initialization Evaluation cout << "Do you want to quit (Y - yes, N - no) : cin >> answer; "; } Sentinel value while (answer != 'Y') { cout << "Welcome to the program. " << endl; cout << "Do you want to quit (Y - Yes, N - No) : cin >> answer; Update statement } cout << "Bye. "; getch(); return 0; ";

WHILE LOOP • Exercise 1: to create a program to calculate and print total of a few numbers and the program will stop and display the result when a value 333 is read.

void main() { int number, total; total= 0; cout << "Enter a number : "; cin >> number; while (number != 333) { total = total + number; cout << "Enter a number : "; cin >> number; } cout <<"You have entered 333 to terminate” <<“the program. “<<endl; cout <<“the total is “<<total; } getch(); Sample data: 10 25 4 6 333 Produce tracing table for the above sample data

EXERCISE OCT 2016

EXERCISE MAR 2013

THE END