Looping

	A loop executes the same statement (simple or compound) over and over, as long as a condition or set of conditions is satisfied.
	A loop is a control structure that causes a statement or group of statements to be executed repeatedly.

The while Statement

	WhileStatement
		While (Expression)
			Statement
	Example:
		while (inputVal != 25)
			cin >> inputVal;
	If the expression has a value of false, the program skips the loop body and execution continues at the statement immediately following the loop.

Phases of Loop Execution

	Loop test – the point at which the while expression is evaluated.
	Loop entry – the point at which the flow of control reaches the first statement of the loop body
	Iteration – an individual repetition of the body of a loop
	Loop exit – the point at which control passes to the first statement following the loop
	Termination condition – the condition causing a loop exit

Loops Using the While Statement

	Count-controlled loop
		Executes a specified number of times
	Event-controlled loop
		Terminates when something changes the expression’s value

Count-Controlled Loops

	A loop control variable is used – it must be initialized before it is tested and it must be updated in the body of the loop.
	Example:
		loopCount = 1;
		while (loopCount <= 10)
		{
			.
			.
			.
			loopCount = loopCount + 1;
		}

Count-Controlled Loops

	A loop control variable is used – it must be initialized before it is tested and it must be updated in the body of the loop.
	Example:
		loopCount = 1;
		while (loopCount <= 10) loop test
		{
			.
			.
			.
			loopCount = loopCount + 1;
		}

Count-Controlled Loops

	A loop control variable is used – it must be initialized before it is tested and it must be updated in the body of the loop.
	Example:
		loopCount = 1;
		while (loopCount <= 10)
		{
			.           loop entry
			.
			.
			loopCount = loopCount + 1;
		}

Count-Controlled Loops

	A loop control variable is used – it must be initialized before it is tested and it must be updated in the body of the loop.
	Example:
		loopCount = 1;
		while (loopCount <= 10)
		{
			.
			. iteration
			.
			loopCount = loopCount + 1;
		}

Count-Controlled Loops

	A loop control variable is used – it must be initialized before it is tested and it must be updated in the body of the loop.
	Example:
		loopCount = 1;
		while (loopCount <= 10)
		{
			.
			.
			.
			loopCount = loopCount + 1;
		}
		loop exit

Count-Controlled Loops

	A loop control variable is used – it must be initialized before it is tested and it must be updated in the body of the loop.
	Example:
		loopCount = 1;
		while (loopCount <= 10) termination condition
		is loopCount = 11
		{
			.
			.
			.
			loopCount = loopCount + 1;
		}

Event-Controlled Loops

	Sentinel-Controlled Loops
		Execute until a special value is encountered
	End-of-File Controlled Loops
		Execute until all data in a file has been read
	Flag-Controlled Loops
		Execute until a flag changes value

Sentinel-Controlled Loops

	A special data value is used to signal the program that there is no more data to be processed.
	A sentinel value must be something that never shows up in the normal input to a program.

Sentinel-Controlled Loop Example

		while (!(month == 2 && day == 31))
		{
		cin >> month >> day;
		.
		.
		.
		}
	Problem: month and day aren’t initialized

More On Sentinel-
Controlled Loops

	cin >> month >> day;
	while (!(month == 2 && day == 31))
	{
	cin >> month >> day;
	.
	.
	.
	}

More On Sentinel-
Controlled Loops

	cin >> month >> day;
	while (!(month == 2 && day == 31))
	{
	cin >> month >> day;
	.
	.
	.
	}
	cin >> month >> day;
	while (!(month == 2 && day == 31))
	{
	.
	.
	.
	cin >> month >> day;
	}

Infinite Loop Example

	cin >> dataValue >> sentinel;
	while (sentinel = 1)
	{
	.
	.
	.
	cin >> dataValue >> sentinel;
	}

End-of-File Controlled Loops

	After a program has read the last piece of data from an input file, the computer is at the end of the file (EOF).
	If we try to input any more values, the stream goes into the fail state.
	We can use the failure of the input stream as a sentinel.
	Example:
		inData >> intVal;
		while (inData)
		{
		cout << intVal << endl;
		inData >> intVal;
		}

More on End-of-File Loops

	Keep in mind that the input stream can fail even though we haven’t reached the end of the file.
	EOF-controlled loops are similar to sentinel-controlled loops in that the program doesn’t know in advance how many data items are to  be input.
	It is possible to use an EOF-controlled loop when we read from the standard input device via the cin stream instead of a data file.

cin EOF Example

	cout << “Enter an integer (or Ctrl-D to quit): ”;
	cin >> someInt;
	while (cin)
	{
	cout << someInt << “ doubled is ”
	<< 2 * someInt << endl;
	cout << “Next number (or Ctrl-D to quit): ”;
	cin >> someInt;
	}

Flag-Controlled Loops

	A flag is a Boolean variable that is used to control the logical flow of a program.
	We can use the Boolean variable to record whether or not the event that controls the process has occurred.

Flag-Controlled Loop Example

	sum = 0;
	nonNegative = true; // Initialize flag
	while (nonNegative)
	{
	cin >> number;
	if (number < 0)
	nonNegative = false; // Test input value
	else // Set flag if event
	sum = sum + number; // occurred.
	}

An Equivalent Loop

	sum = 0;
	negative = false;      // Initialize flag
	while (!negative)
	{
	cin >> number;
	if (number < 0)
	negative = true;     // Test input value
	else      // Set flag if event
	sum = sum + number;  // occurred.
	}

Another Equivalent Loop

	sum = 0;
	cin >> number;
	while (number > 0)      // Test input value
	{
	sum = sum + number;
	}