CONTROL STRUCTURES
(MULTI-WAY SELECTION)
MULTI-WAY SELECTION
EXTENDED IF-ELSE
Used to select exactly one task out of multiple tasks
(or possibly none)
Unlike a series of “ifs” evaluation stops once one
relational expression evaluates as true (others are skipped)
Always does on less evaluation than a series of “ifs”
Well planned implementation provides for efficiency –
most common choice is listed first
MULTIPLE SELECTION
EXTENDED IF-ELSE - SIMPLE
 if ( relational expression(s) )
statement;
else
if ( relational expression(s) )
statement;
else
if ( relational expression(s) )
statement;
else
statement;
MULTI-WAY SELECTION
EXTENED IF-ELSE - COMPOUND

if ( relational expression(s) )
{
statement;
statement(s);
}
else
if ( relational expression(s) )
{
statement;
statement(s);
}
else
if ( relational expression(s) )
{
statement;
statement(s);
}
MULTI-WAY SELECTION
RULES
1. First statement(s) will be executed if and only if the
evaluation of the relational expression(s) is/are true.
2. Second statement(s) will be executed if and only if
the evaluation of the first relational expression(s)
is/are false and if and only if the evaluation of the
second relational expression(s) is/are true.
3. Same progression as 1 and 2 for all levels that exist.
Note: This process does not have to end with two, three or four
selections, but can continue for as many selections as needed.
MULTIPLE SELECTION
EXAMPLES:
if (numStudents< 6)
salary = hours * CLUSTER_RATE;
else
if (numStudents < 12)
salary = hours * LIMITED_RATE;
else
salary = hours * FULL_RATE
MULTIPLE SELECTION
EXAMPLES:
if (temperature <= 10)
cout << “Go Bowling” << endl;
else
if (temperature <= 32)
cout << “Go Skiing” << endl;
else
if (temperature <= 70)
cout << “Play Football” << endl;
else
if (temperature <= 85)
{
cout << “Play Tennis” << endl;
cout << “Wear white!” << endl;
}
else
cout << “Go Swimming” << endl;
if (temperature > 85)
cout << “Go Swimming” << endl;
else
if (temperature > 70)
{
cout << “Play Tennis” << endl;
cout << “Wear white!” << endl;
}
else
if (temperature > 32)
cout << “Play Football” << end;
else
if (temperature > 10)
cout << “Go Skiing” << endl;
else
cout << “Go Bowling” << endl;
MULTI-WAY SELECTION
NESTED IF-ELSE
Situations where action is dependent upon
two or more different conditions
Examples:
if (gender == ‘M’)
if (age < MAX_AGE)
cout << “Male and under 67.” << endl;
else
cout << “Male and 67 or over.” << endl;
else
if (age < MAX_AGE)
cout << “Female and under 67.” << endl;
else
cout << “Female and 67 or over.” << endl;
if (savings >= DOLLAR_LIMIT)
if (vacation >= VACATION_LIMIT)
cout << “Trip to Hawaii” << endl;
else
cout << “Vacation at local ski resort.” << endl;
else
cout << “Go camping in mountains.” << endl;
MULTI-WAY SELECTION
SWITCH
Alternate form of multi-way selection
Decision can only be made on integral or
enumerated data types (bool, char, int)
Does not work with strings or floating point
numbers
Only works when testing for specific values
Does not work with ranges
MULTI-WAY SELECTION
SWITCH - SIMPLE
switch (selector)
{
case choice1:
case choice2:
case choice3:
“
case choice(n):
}
statement;
break;
statement;
break;
statement;
break;
“
statement;
MULTI-WAY SELECTION
SWITCH – WITH DEFAULT
switch (selector)
{
case choice1:
case choice2:
“
case choice(n):
default:
}
statement;
break;
statement;
break;
“
statement;
break;
statement;
statement(s);
MULTIPLE SELECTION
SWITCH – COMPOUND
 switch (selector)
{
case choice1:
case choice2:
“
case choice(n):
default:
}
statement;
statement(s);
break;
statement;
statemant(s);
break;
“
statement;
statement(s);
break;
statement;
statement(s);
MULTIPLE SELECTION
RULES
1. Selector may only be an integral data type (int,
char, bool, or enumerated).
2. Corresponding statement(s) is/are executed if choice
is equal to the selector.
3. After corresponding statement(s) are executed if
break is not present additional case statements are
executed until a break is found or end of structure is
found.
4. If no choice is equal to the selector, the switch is
exited unless a default is available.
MULTIPLE SELECTION
EXAMPLES:
switch(category)
{
case 1: cout << “Category One” << endl;
break;
case 2: cout << “Category Two” << endl;
break;
:
:
case n: cout << “Category n” << endl;
break;
}
MULTI-WAY SELECTION
EXAMPLE:
int num1, num2, answer;
char choice;
cout << "Enter two numbers, separated by a space: ";
cin >> num1 >> num2;
cout << endl << endl;
cout << "Perform which operation on the Numbers?" << endl;
cout << " a - Add" << endl;
cout << " s - Subtract" << endl;
cout << " m - Mulitply" << endl;
cout << " d - Divide" << endl;
cout << "Enter your choice from above: " << endl;
cin >> choice;
choice = tolower (choice);
switch (choice)
{
case 'a‘: answer = num1 + num2;
cout << "The sum is " << answer << endl;
break;
case 's‘: answer = num1 - num2;
cout << "The difference is " << answer << endl;
break;
case 'm‘: answer = num1 * num2;
cout << "The product is " << answer << endl;
break;
case 'd‘: answer = num1 / num2;
cout << "The quotient is " << answer << endl;
break;
default : cout << "Invalid choice entered!" << endl;
} // end switch
MULTI-WAY SELECTION
EXAMPLE:
char answer;
cout << "Would you like to continue [Y] or [N]?" << endl;
cin >> answer;
switch (answer)
{
case 'Y':
case 'y‘:
case 'N':
case 'n‘:
default :
cout << "You chose yes" << endl;
cout << "Way to go." << endl;
break;
cout << "You chose no" << endl;
cout << "Not very positive." << endl;
break;
cout << "You were suppose to choose Y or N." << endl;
cout << "What happened?" << endl;
} // end switch