CSC133 Intro to CS Using C++

Selection

Selection statements allow the program to perform different statements based on some condition. The condition usually consists of a comparison of two or more values. Simple comparisons are performed with relational operators. In C++ the relational operators are:

Symbol	Meaning
==	equal
!=	not equal
<	less than
>	greater than
<=	less than or equal to
>=	greater than or equal to

Here are some examples of pseudocode for selection operations:

   read time
   if time is 5pm
      print "go home"

   read gender
   if gender is female
      print "Dear Madam"
   else
      print "Dear Sir"

   read cholesterol
   if cholesterol >= 200
      print "your cholesterol is too high"
      print "please see your doctor"
   else if cholesterol >= 190
      print "be careful...your cholesterol is borderline"
   else
      print "your cholesterol is ok"

Notice that we indent the statement(s) that come after the if, and the statement(s) that come after the else. Without this the program is very difficult to read.

In C++, the condition in an if statement is always enclosed in parentheses. If more than one statement is needed after the if or the else, they must be surrounded by braces { }, If only one statement is needed after the if or the else, then braces are optional. Here are some examples of C++ code containing if statements:

    cout << "Enter f for female or m for male: ";
    cin >> gender;
    if (gender == 'f')
       cout << "Dear Madam";
    else
       cout << "Dear Sir";


    cout << "Enter department number: ";
    cin >> deptnum;
    cout << "Enter item cost: ";
    cin >> cost;
    if (deptnum == AUDIO)     // audio items are 10% off
       cost = cost * .9;
    tax = cost * taxrate;
    totalcost = cost * tax;

    cout << "Enter department number: ";
    cin >> deptnum;
    cout << "Enter item cost: ";
    cin >> cost;
    if (deptnum != VIDEO)     // all items except video are 15% off
       cost = cost * .85;
    tax = cost * taxrate;
    totalcost = cost * tax;

    cout << "Enter item cost: ";
    cin >> cost;
    if (cost <= 200)
       cost = cost * .92;    // items under $200 are 8% off
    else
       cost = cost * .88;    // items over $200 are 12% off
    tax = cost * taxrate;
    totalcost = cost * tax;