LoopingROBERT REVAES

Logical Operators

&& AND Both have to be true for it to evaluate to be true.

|| OR One or the other has to be true for it to evaluate to be true.

! NOT Returns the opposite result.

Testing the State of an I/O Stream

C++ provides a way to check whether a stream is in the fail state.

ifstream myIn; myIn.open(“measures.dat”); if(!myIn) {

cout << “Can’t open the input file.”; return 1;

}

The While Statement

Loop executes the same statement over and over, as long as a condition or set conditions is satisfied.

while( Expression) Statement

Ex: while (inputVal != 25)

cin >> inputVal;

The statement to be executed each time through the loop is called the body of the loop.

Phases of Loop Execution

The body of a loop is executed in several phases: The moment that the flow control reaches the first statement inside

the loop body is the loop entry. Each time the body of a loop is executed, a pass is made through the

loop. This pass is called an iteration. Before each iteration, control is transferred to the loop test at the

beginning of the loop. When the last iteration is complete the flow of the control has passed

to the first statement flowing the loop, the program has exited the loop.

The condition that causes a loop to be exited is the termination condition.

Loops

Two major types of loops: count-controlled

Repeat a specified number of times. event-controlled loops

Repeat until something happens within the loop.

Count-Controlled Loops

Uses a variable we call the loop control variable in the loop test.

Ex: int loopCount = 1; while (loopCount <= 10) {

cout << “Hello!” << endl; loopCount++;

}

Variables used in the way loopCount is used are called counters.

Event-Controlled Loops

Several kinds of event-controlled loops exist: sentinel controlled

Some special value that that will never show up in normal input. end-of-file controlled

After a program has read the last piece of data from an input file, it’s in a successful state.

flag controlled A Boolean variable that tis used to control the logical flow of a program.

Looping Subtasks

Three common tasks: counting

Keep track of the number of times the loop has been executed. summing

Sum a set of data values. keeping track of a previous value

Remember the previous value that was read from input.