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What is a loop?. A loop is a repetition control structure. it causes a single statement or block to be executed repeatedly. Two Types of Loops. count controlled loops repeat a specified number of times event-controlled loops

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Presentation Transcript
what is a loop
What is a loop?
  • A loop is a repetition control structure.
  • it causes a single statement or block to be executed repeatedly
two types of loops
Two Types of Loops

count controlled loops

repeat a specified number of times

event-controlled loops

some condition within the loop body changes and this causes the repeating to stop

while pretest loop
While (pretest loop)

SYNTAX

while ( Expression)

{ .

. // loop body

.

}

NOTE: Loop body can be a single statement, a null statement, or a block.

slide4
When the expression is tested and found to be false, the loop is exited and control passes to the statement which follows the loop body.

WHILE LOOP

FALSE

Expression

TRUE

body

statement

slide5

Count-controlled loop contains

an initialization of the loop control variable

an expression to test for continuing the loop

an update of the loop controlvariable to be executed with each iteration of the body

count controlled loop
Count-controlled Loop

int count ;

count = 4; // initialize loop variable

while (count > 0) // test expression

{

cout << count << endl ; // repeated action

count = count – 1;// update loop variable

}

cout << “Done” << endl ;

count controlled loop1

count

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count = count - 1;

}

cout << “Done” << endl ;

OUTPUT

count controlled loop2

count

4

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

count controlled loop3

count

4

Count-controlled Loop

int count ;

count = 4;

while (count > 0) TRUE

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

count controlled loop4

count

4

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

count controlled loop5

count

3

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

count controlled loop6

count

3

Count-controlled Loop

int count ;

count = 4;

while (count > 0) TRUE

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

count controlled loop7

count

3

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

count controlled loop8

count

2

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

count controlled loop9

count

2

Count-controlled Loop

int count ;

count = 4;

while (count > 0) TRUE

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

count controlled loop10

count

2

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

2

count controlled loop11

count

1

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

2

count controlled loop12

count

1

Count-controlled Loop

int count ;

count = 4;

while (count > 0) TRUE

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

2

count controlled loop13

count

1

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

2

1

count controlled loop14

count

0

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

2

1

count controlled loop15

count

0

Count-controlled Loop

int count ;

count = 4;

while (count > 0) FALSE

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

2

1

count controlled loop16

count

0

Count-controlled Loop

int count ;

count = 4;

while (count > 0)

{

cout << count << endl ;

count --;

}

cout << “Done” << endl ;

OUTPUT

4

3

2

1

Done

example
Example
  • Use a while loop to read the 100 blood pressures and find their total
  • int thisBP ;
  • int total ;
  • int count ;
  • count = 0 ; // initialize
  • while ( count < 100 )// test expression
  • {
  • cin >> thisBP ;
  • total = total + thisBP ;
  • count++ ; // update
  • }
  • cout << “The total = “ << total<<endl;
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