Repetition Control Statements in C++

Also know as looping statements, or loops. These statements execute the statement(s) repeatedly until condition remains true. Allows programmer to specify that a program shall repeat an action while some condition remains true. Types of repetition control statement includes

While Statement

It executes the statement(s) repeatedly until condition remains true (Iteration). Statements contained in the while constitutes body of the while statement which can be a single statement or a block. As condition becomes false, loop is terminated and control is transferred to the statement after the repetition statement executes

Syntax:

initialization; 
while (loopContinuationCondition)
{
Statement;
Increment;
}

Example:

int product = 3;
while ( product <= 100 ) {
  product = 3 * product;
}

Assignment Exercise:

A class of ten students take a quiz. The grades ( integers in the range of 0 to 100) for this quiz are available to you. Calculates and display the total of all student grades and the class average on the quiz.

C++ Example

int main(void)
{
int counter = 1; // Declare and initialize loop variable
while (counter {
cout< counter++; // Incremental control variable by 1
} // End of while
getch();
return 0;
}

Another Example

int main(void)
{
int counter = 0; 	 // Declare and initialize loop variable
while (++counter <=10) {   // Loop continuation condition &
  // Increment
  cout<<counter<<"  ";
}
getch();
return 0;
}

For Statement

Another type of loop statement – for loop. It specifies the counter control repetition details in a single line of code. When the for statement begins execution, the control variable is declared and initialized. Then the loop – continuation condition is checked and if condition is true, body executes. At the end counter is incremented or decremented.

Syntax:

Example:

int main(void)
{
for (int counter = 1; counter <=10; counter++ ){
   cout<<counter<<"  ";
}
getch();
return 0;
}

Few Examples Using “for” statement

 for ( int i = 1;  i <=100;  i++ )

 for ( int i = 100;  i >=1;  i-- )

 for ( int i = 7;  i <=77;  i+=7 )

  for ( int i = 20;  i >=2;  i -=2 )

  for ( int i = 2;  i <=20;  i += 3 )

  for ( int i = 99;  i >=0;  i -= 11 )

do…while Statement

This control statement is similar to the while statement. In the while statement, the loop continuation condition is checked at the beginning of the loop before the body of loop executed. The do…while statement tests the loop-continuation condition after the loop body executes. Therefore the loop body always executes at least once.

When the do…while terminates, execution continues with the statement after the while clause. Note that it is not necessary to use braces in the do…while  if there is only one statement in the body. However most programmer include the braces to avoid confusion between the while and do…while statements.

We can use a do…while statement to implement the data-validation loop -  a loop that continues to prompt and read data until valid data item is entered.

Syntax:

initialization; 
do
{
  Statement;
  Increment;
}
while (loopContinuationCondition);

Example:

int main(void)
{
int counter = 1;
do
{
  cout<<counter<<"  ";
  counter++;
}
while (counter <=10);
getch();
return 0;
}

Review of repetition control statements

while loop

• Convenient when at least one repetition of loop body is needed

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