Lecture 4 c++

Basic Control Flow: Repetitions and Loop Statements

TCB2073Structured Programming & Database

Systems

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Objectives

By the end of this lecture, you will be able to: describe the C++ repetition structures (while, for, do..while)

design and implement a C++ program that involves repetition structures

use SENTINEL in a do .. while statement desk check loop statement

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Control Structures Revisit

Sequence Selection Repetition

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C++ Repetition Structures

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Terms

loop a control structure that repeats a group of steps in a program.

loop body the statements that are repeated in the loop.

counter-controlled loop (counting loop) a loop whose required number of iterations can be determined before loop execution begins

loop repetition condition the condition that controls loop repetition

loop control variable the variable whose value controls loop repetition

infinite loop a loop that executes forever

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General Flowchart for while Statement (counter-controlled loop)

initialisation

testing

updating

Loop body

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While Statement Syntax

SYNTAX: while (loop repetition condition)statement

EXAMPLE: /*display N asterisks */count_star = 0;while (count_star < N) {

cout << ” * ”;count_star = count_star + 1;

}

INTERPRETATION : The statements in the body loop are repeated as long as the loop repetition condition is true. The while loop is exited when the repetition condition is false

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Problem 1: Print N (qty) asterisks

Perform desk check!

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Problem 2: Descending order (N to 0)

Perform desk check!

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Problem 3: Sum a series of N numbers

Perform desk check!

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Problem 4: Find the average of a series of N numbers

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do .. while statement

executes the statements in the loop body at least once

Loop body

updating

testing

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for Statement Syntax

SYNTAX: for (initialisation expression;loop repetition condition;update expression)statement

EXAMPLE: /*display N asterisks */for (count_star = 0;

count_star < N;count_star++) {cout <<” * “;

}

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Problem 1: Print N (qty) asterisks

Perform desk check!

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Problem 2: Descending order (N to 0)

intialisation

testing

updating

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do .. while statement

executes the statements in the loop body at least once

Loop body

updating

testing

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do .. while statement syntax

SYNTAX: do {statement

} while(loop repetition condition);

EXAMPLE: /*display N asterisks */count_star = 0;do { cout <<“ * ”; count_star++;} while (count_star < 5);

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do .. while Counting Stars

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Problem 3: to sum N numbers, without knowing N

updating

testing

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SENTINEL

Sentinel value an end marker that follows the last item in a list of data

e.g#define SENTINEL 999

List of data:56 90 85 100 72 45 999

Sentinel value

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Problem #1

Write a nested loop to produce the following pattern if the user input is 5

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Problem #2

Write a nested loop to produce the following pattern if the user input is 5

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Problem #3

Write a nested loop to produce the following pattern if the user input is 5

TBB1073 : Basic Control Flow -Repetition and loop statements

Summary

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