2.4 Repetition statements, arrays and structured programming  (Page 2/8)

statements;

}

The flow chart of the while statement is given below.

Example

// this program computes the sum of 10 first integers starting from 1

#include<iostream.h>

int main()

{

const int N = 10

int sum = 0;

int count = 1; // initialize count

while (count<= N){

sum = sum + count;

count++; // increment count

}

cout<<“The sum is “<<sum<<endl;

return 0;

}

The output of the above program:

The sum is 55

In the above program, the loop incurs a counter-controlled repetition. Counter-controlled repetition requires:

1. the name of a control variable (the variable count in this case);
2. the initial value of the control variable ( count is initialized to 1 in this case)
3. the condition that tests for the final value of the control variable (i.e., whether looping should continue) ;
4. the increment (or decrement) by which the control variable is modified each time through the loop.

Example

#include<iostream.h>

int main()

{

int i;

i = 10;

while (i>= 1)

{

cout<<i<<" ";

i--; // subtract 1 from i

}

return 0;

}

The output of the above program:

1. 9 8 7 6 5 4 3 2 1

Interactive while loops

Combining interactive data entry with the repetition capabilities of the while statement produces very adaptable and powerful programs.

Example

// Class average program with counter-controlled repetition

#include<iostream.h>

int main()

{

int total, // sum of grades

gradeCounter, // number of grades entered

grade, // one grade

average; // average of grades

// initialization phase

total = 0;

gradeCounter = 1; // prepare to loop

while ( gradeCounter<= 10 ) { // loop 10 times

cout<<"Enter grade: "; // prompt for input

cin>>grade; // input grade

total = total + grade; // add grade to total

gradeCounter = gradeCounter + 1; // increment counter

}

// termination phase

average = total / 10; // integer division

cout<<"Class average is "<<average<<endl;

return 0;

}

The following is a sample run of the above program:

Enter grade: 98

Enter grade: 76

Enter grade: 71

Enter grade: 87

Enter grade: 83

Enter grade: 90

Enter grade: 57

Enter grade: 79

Enter grade: 82

Enter grade: 94

Class average is 81

Sentinels

In programming, data values used to indicate either the start or end of a data series are called sentinels. The sentinel values must be selected so as not to conflict with legitimate data values.

Example

#include<iostream.h>

int main()

{

float grade, total;

grade = 0;

total = 0;

cout<<"\nTo stop entering grades, type in any number less than 0.\n\n";

cout<<"Enter a grade: ";

cin>>grade;

while (grade>= 0 )

{

total = total + grade;

cout<<"Enter a grade: ";

cin>>grade;

}

cout<<"\nThe total of the grades is "<<total<<endl;

return 0;

}

The following is a sample run of the above program:

To stop entering grades, type in any number less than 0.

Enter a grade: 95

Enter a grade: 100

Enter a grade: 82

Enter a grade: -2

The total of the grades is 277

Break statement

The break statement causes an exit from the innermost enclosing loop statement.

Example:

while( count<= 10)

{

cout<<“Enter a number: “:

cin>>num;

if (num>76){

cout<<“you lose!\n”;

break;

}

else

cout<<“Keep on trucking!\n”;

count++;

}

//break jumps to here