2.4 Repetition statements, arrays and structured programming  (Page 3/8)

The break statement violates pure structured programming principles because it provides a second, nonstandard exit from a loop.

However, it is useful and valuable for breaking out of loops when an unusual condition is detected.

Continue statements

The continue statement halts a looping statement and restarts the loop with a new iteration.

while( count<30)

{

cout<<“Enter a grade: “;

cin>>grade;

if (grade<0 || grade>100)

continue;

total = total + grade;

count++;

}

In the above program, invalid grades are simply ignored and only valid grades are added to the total.

The null statement

All statements must be terminated by a semicolon. A semicolon with nothing preceding it is also a valid statement, called the null statement. Thus, the statement

;

is a null statement.

Example:

if (a>0)

b = 7;

else ;

The null statement is a do-nothing statement.

For loops

The for statement is used for repeating a statement or series of statements as long as a given conditional expression evaluates to true.

One of the main differences between while statement and for statement is that in addition to a conditional expression, you can also include code in the for statement

• to initialize a counter variable and
• changes its value with each iteration

The syntax of the for statement:

for ( initialization expression; condition; update statement){

statement(s);

}

In its most common form, the initialization expression consists of a single statement used to set the starting value of a counter variable, the condition contains the maximum or minimum value of the counter variable can have and determines when the loop is finished, and the update statement provides the increment value that is added to or subtracted from the counter variable each time the loop is executed.

The flowchart of the for statement is given below.

Example

#include<iostream.h>

int main()

{

int sum = 0;

for (int number = 2; number<= 100; number += 2)

sum += number;

cout<<“Sum is “<<sum<<endl;

return 0;

}

The output of the above program:

Sum is 2550

Example

In this example, we have to solve the following problem:

A person invests $1000.00 in a saving account with 5 percent interest. Assuming that all interest is left on deposit in the account, calculate and print the amount of money in the account at the end of each year for 10 years. Use the following formula for determining these amounts:

a = p(1 + r)^n

where p is the original amount invested, r is the annual interest rate and n is the number of years and a is the amount on deposit at the end of the nth year.

#include<iostream.h>

#include<iomanip.h>

#include<math.h>

int main()

{

double amount,

principal = 1000.0,

rate = 0.05;

cout<<"Year”<<setw(21)

<<"Amount on deposit"<<endl;

cout<<setiosflags(ios::fixed | ios::showpoint)<<setprecision(2);

for (int year = 1; year<= 10; year++)

{

amount = principal*pow(1.0 + rate, year);

cout<<setw(4)<<year

<<setw(21)<<amount<<endl;

}

return 0;

}

The output of the above program:

YearAmount on deposit

1 1050.00

1. 1102.50
2. 1157.62
3. 1215.51
4. 1276.28
5. 1340.10
6. 1407.10
7. 1477.46
8. 1551.33
9. 1628.89

Nested loops

In many situations, it is convenient to use a loop contained within another loop. Such loops are called nested loops .