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

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`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:

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.

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`

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