Chapter 4 Control Structure: Loop Knowledge: Understand the various concepts of loop control...

Chapter 4 Control Structure: Loop

Knowledge:Understand the various concepts of loop control structure

Skill:Be able to develop a program involving loop control structure

Prof. Kuanquan Wang

The School of Computer Science and Technology

Harbin Institute of technology

Outline

4.1 Review and introduction to loop flow control structure

4.2 Loop control with counter4.3 Loop control with condition test4.4 Loop control with sentinel

4.1 Review and introduction to loop flow control structure

How many basic flow control structure?

There are 3 kinds of basic flow control structure.

Sequence Selection Repetition or loop

C Programming LanguageC Programming Language 44

How Loops are Controlled?How Loops are Controlled?

Sentinel ControlledCounter Controlled

•1, 2, 3, 4, …•…, 4, 3, 2, 1

Condition Controlled

4.2 Counter Controlled Loop4.2 Counter Controlled Loop

counter ← initial Value

test counter value

Step n

Step x

Update counter

Counter Controlled LoopCounter Controlled Loop

counter = initialValue

test counter value

Step n

Step x

Update counter

counter ← initial Value

Example:Example:

Can you identify the input and output???

Draw a flowchart for the following problem:

Read 5 integer and display the

value of their summation.

Input : 5 integer n1, n2, n3, n4, n5 Output: The summation of

n1, n2, .., n5

Input example: 2 3 4 5 6

Output example: 20

Input n1

Input n2

Input n3

input n4

input n5

output sum

sum ← n1+n2+n3+n4+n5

Assume input example: 2 3 4 5 6

This flowchart does not use loop, hence

we need to use 6 different variables

Counter-Counter-Controlled Controlled LoopLoop

counter ← 1, sum ← 0

counter < 6

sum ← sum + n

counter++

output sum

input n

1counter

1 < 6 true

0 + 22

2 < 6 true

2 + 35

3 < 6 true

5 + 49

4 < 6 true

9 + 514

5 < 6 true

14 + 620

6 < 6 false

Assume input example:

2 3 4 5 6

This loop iscounter-controlled

The counter Increases by 1

Uses only 3 variables

Decreasing Counter-Controlled LoopDecreasing Counter-Controlled Loop

counter ← 5, sum ← 0

counter > 0

sum←sum+ x

counter--

output sum

input x

Loop : Loop : forfor

Condition is tested first Loop is controlled by a counter Syntaxes

for (initial value ; condition; update counter) statement;

for (initial value ; condition; update counter) {statement;statement;

i ← 0, sum ← 0

sum←sum+ x

output sum

input x

int x, sum, i;sum = 0;for (i = 0; i < 5; i++) {

scanf(“%d”,&x);sum = sum + x;

}printf(“%d”,sum);

forfor statement statement

Example:

for ( num = 1; num <= 3; num++ ) printf(“%d\t”, num);

1 _printf(“have come to exit\n”);

Example:

for (num = 1; num <= 3; num++ ) printf(“%d\t”, num);

printf(“have come to exit\n”);

Example:

1 2 3 _

Example:

1 2 3 _

Example:

1 2 3 _

Example:

1 2 3 have come to exit_

Loop StructureLoop Structure

Condition is tested first Condition is tested later

4.3 Loop control with condition test

Testing Condition First

condition

Step x

Step y

Step a

Step n

Testing Condition First

condition

Step x

Step y

Step a

Step n

Loop: whileLoop: while

Condition is tested first Loop is controlled by condition or a counter Syntax

while (condition) statement;

Orwhile (condition) {

statement;statement;

Step a

condition

Step n

Step x

Step y

Testing condition later

Step a

condition

Step n

Step x

Step y

Testing condition later

Do-while LoopDo-while Loop Statements in the loop are executed first (at least

once), and condition is tested last Loop is controlled by a condition or counter Syntax

do { statement;statement;

} while (condition);statement;

Example: Draw a flowchart for this problem;

Given an exam marks as input, display the appropriate message based on the rules below:

If marks is greater than 49, display “PASS”, otherwise display “FAIL”

However, for input outside the 0-100 range, display “WRONG INPUT” and prompt the user to input again until a valid input is entered

Condition-ControlledCondition-Controlled LoopLoop

input m

m<0 || m>100

m>49 “PASS”

“FAIL”

“WRONG INPUT”

Assume m=110

110 < 0 || 110 >100

WRONG INPUT

Assume m=5

5 < 0 || 5 >100

5 > 49

Assume m=57

57 < 0 || 57 >100

57 > 49

Condition-controlled loop with its condition being tested at the end

input m

m<0 || m>100

m>49 “PASS”

“FAIL”

“WRONG INPUT”

input m

Condition-controlled loop with its condition being tested first

int marks;scanf(“%d”,&marks);while (marks<0) | | (marks>100) {

printf(“WRONG INPUT”);scanf(“%d”,&marks);

}if (marks>49) {

printf(“PASS”);else

printf(“FAIL”);}

DoubleSelection

do-while statementdo-while statement

Example :printf(“Input start and end value : “);scanf(“%d %d”, &start, &end);do {

printf(“%c (%d)\n“, start, start);start++;

} while (start <= end) ;

Input start and end value : _Input start and end value : 65 67_

Input start and end value : 65 67A (65)_

66 <= 67

Input start and end value : 65 67A (65)B (66)_

67 <= 67

Input start and end value : 65 67A (65)B (66)C (67)_

68 <= 67

4.4 Sentinel-Controlled Loop4.4 Sentinel-Controlled Loop

Draw a flowchart for a problem which:

Receive a number of positive integers and display the summation and average of these integers.

A negative or zero input indicate the end of input process

Can you identify the input and output???

Input: A set of integers ending with a

negative integer or a zero

Output: Summation and Average of these integers

Input Example:

30 16 42 -9

Output Example:

Sum = 88

Average = 29.33

Sentinel Value

Now…What have you

understand?

sum←sum+x

input x

sum←0

input x

display sum

Try to understand What will happen if this statement is deleted???

What happened if these 2

statements exchange

places

sum←sum+x

input x

ExerciseExercise Given a set of integers

with the last one being 999 Display the summation of

all the integers.

Input example: 1 3 23 999

Output example: Sum = 27

Draw the flowchart for this problem

Sentinel-controlled loop

x!=999

sum←sum+x

input x

output sum

#include <stdio.h>

void main() {

int sum, x;

sum = 0;

scanf(“%d”, &x);

while (x != 999) {

sum = sum + x;

scanf(“%d”, &x);

printf(“The sum : %d\n”, sum);

int sum, x; sum = 0; scanf(“%d”, &x); while (x != 999) { sum = sum + x; scanf(“%d”, &x); } printf(“\nThe sum : %d\n”, sum);

1 != 999

33 != 999

1 3 23

2323 != 999

4+2327

1 3 23 999

999999 != 999

The sum : 27

Now…Let us have a

summary!The concept of Loop Structure

3 methods to control loop structure

Counter Controlled, Condition Controlled, Sentinel Controlled

3 statements in C language

for, while, do while

Thank you for your attention!

Now let us have a break!

Chapter 4 Control Structure: Loop Knowledge: Understand the various concepts of loop control...

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