Highlights of this lab:

So far we learned three control structures: the sequence, the If statement, and the While statement. This lab will provide you more control structures. They are

• Switch statement,
• Do-while statement, and
• For statement.

• You should be able to construct switch statements.
• You should be able to construct while loop, do-while loop, and for loop.
• You should be able to exchange a count-controlled while loop and a for loop.

NOTE: The Exercises will be marked in the lab.

A Switch Statement

Here is the syntax template for the Switch statement:

switch ( IntegralOrEnumExpression ) {

    SwitchLabel ... Statement
		.
		.
		.
}

IntegralOrEnumExpression is an expression of integral type — char, short, int, long, bool or of enum type which will be discussed later.

SwitchLabel

	case ConstantExpression:
	default :

Now let's look at the following C++ code:

   switch (grade)
	{
		case 'A': cout << "Great work. " << endl;
			  break;
		case 'B': cout << "Good work. " << endl;
			  break;
		case 'C': cout << "Passing work. " << endl;
			  break;
		case 'D':
		case 'F': cout << "Unsatisfictory work. " << endl;
			  cout << "See your instructor." << endl;
			  break;
		default:  cout << grade << " is not a legal grade." << endl;
			  break;
	}

The value in grade is compared with the value in each case label. When a match is found, the corresponding statement is executed. If the value of the switch expression does not match a value in any case label, the default label is matched by default.

Because execution continues after a match until break is encountered, both 'D' and 'F' send the same message to the screen. What would happen if we forgot to put break after the statement associated with case 'B'? Every time grade contained a B both "Good work!" and "Passing work!" would be printed.

Do-while loop

do 
	Statement
while (Expression);

do {
    cout << "Please enter a mark: ";
    cin >> mark;
    if (mark < 0 || mark > 100)
       cout << "Invalid mark. Try again.  " << endl << endl;

} while (mark < 0 || mark > 100);

	sum = 0;
	counter = 0;
	do {
       	    cout << "Please enter a mark: ";
	    cin >> mark;
	    sum = sum + mark;
	    counter++;
	} while (counter < 10);

	cout << "The average of the marks entered is " << sum/counter << endl;

For Loops

The syntax template of a for statement is:

for (InitStatement; Expression1; Expression2)
	Statement

The following for loop reads 10 marks and sums them up.

sum = 0;
for (counter = 1; counter <= 10; counter++) {
       	cout << "Please enter a mark: ";
	cin >> mark;
	sum = sum + mark;
}

sum = 0;
for (counter = 10; counter > 0; counter--) {
       	cout << "Please enter a mark: ";
	cin >> mark;
	sum = sum + mark;
}

sum = 0;
counter = 1; 
while (counter <= 10) {
       	cout << "Please enter a mark: ";
	cin >> mark;
	sum = sum + mark;
	counter++;
}

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Lab Exercise — Additional Control Structures

Exercise 1: (This exercise will be marked in the lab.)

• Type the following code into a file named case.cpp using Emacs (emacs case.cpp &).

  /************************************************************ * * FileName: case.cpp * Author: Ricky J. Sethi * Purpose: Demonstrate how to use Switch Statemenet. * **************************************************************/ #include <iostream> using namespace std; int main() { char grade; cout << "Please enter a character grade (A, B, C, D, or F): "; cin >> grade; switch (grade) { case 'A': cout << "Great work. " << endl; break; case 'B': cout << "Good work. " << endl; break; case 'C': cout << "Passing work. " << endl; break; case 'D': case 'F': cout << "Unsatisfictory work. " << endl; cout << "See your instructor." << endl; break; default: cout << grade << " is not a legal grade." << endl; break; } return 0; } // end program

  The purpose of the program is to demonstrate how to use switch statement.

• Please add a for loop so that the program will ask the user for 6 input grades and print out the corresponding message in each run.
• Compile and run this C++ program. Use input value A, B, C, D, E, and F.

Exercise 2: (This exercise will be marked in the lab.)

• Type the following code into a file named loop.cpp using Emacs (emacs loop.cpp &).

  /*********************************************************** * * FileName: loop.cpp * Author: Ricky J. Sethi * Purpose: Demonstrate how to use For loop and * Do-while Statemenet. For loop will * handle 10 valid marks and printout the * average. A structure which has a loop * inside another loop is called a nested loop. * **************************************************************/ #include <iostream> using namespace std; int main() { int mark; int sum; char grade; sum = 0; for (int counter =1; counter <= 10; counter++) { //write a do-while loop here to obtain a valid mark //a valid mark means that the mark is greater than or equal to 0 //and less than or equal to 100. sum = sum + mark; if (mark >= 90) grade = 'A'; else if (mark >= 80 && mark < 90) grade = 'B'; else if (mark >= 70 && mark < 80) grade = 'C'; else if (mark >= 50 && mark < 70) grade = 'D'; else grade = 'F'; cout << "The corresponding character grade is " << grade << endl; } cout << endl; cout << "The average of the ten marks is " << sum/10 << endl; return 0; } // end program

• Complete the program by adding a do-while loop.
• Compile and run this C++ program. Try the following input values -10, 0, 101, 100, 40, 50, 60, 70, 80, 90, 85, and 98.

Exercise 3: (This exercise will be marked in the lab.)

• Change the for loop in the loop.cpp to a while loop.
• Compile and run this C++ program. Try the following input values -10, 0, 101, 100, 40, 50, 60, 70, 80, 90, 85, and 98.
• Perform a typescript (using the script loop.log command) capture of the program run to obtain the loop.log and print out this loop.log.

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Hand In: This lab handout with the answers filled in attached to a listing of your final exercises
(use the enscript command from your Programming Style Sheet to print it out:
enscript -E -G -2rj -M Letter -PECT2_PS <filename> or a2ps <filename>).