Chapter
1
Introduction
Chapter 2
Functions
Chapter 3
Branching
Chapter 4
Iteration
Chapter 5
OOP
Chapter 6
Arrays
|
CHAPTER 3
( Branching )
1 )
Branching
2 ) Include Files
When
instructions within a program are executed one
after the other sequentially that program is said to have a
linear structure. Decision making after examining all
available options is very important in life as well as in
programming. For example, it is the law that all males 18 or
older should register with the selective service. If you are
writing a program to send out reminders to enforce this law,
the decision to send the letter should be based on if a person
is male and if he is 18 or older. In this chapter you will
learn how to write statements that make decisions.
A simple program to look at an average grade of a student and display
if that student passed or failed would look like this
(Program 3-1):
|
Program 3-1.
| /****************************************
Accept three
grades, find the average
and display
Passed or Failed.
Teach objective
- making decisions
By Dr. John
Abraham
Created for
1380 students
*****************************************/
#include
<iostream.h>
#include
<iomanip.h> //to format input and output.
//Here setw and
endl require it
float findave
(int &, int &, int &);
int main
()
{
int one, two,
three;
float
average;
average=
findave (one, two, three);
cout <<
"Three grades are: " <<one <<setw(4)<<two
<<setw(4)<<three <<endl;
//endl inserts
line feed and carriage return
cout <<
"The average is : " <<average <<endl;
if (average
>= 70) cout << "Student passed the
course!";< /FONT>
else cout
<< "Student failed the course!";
return
(0);
}
float
findave(int &one, int &two, int &three)
{
cout <<
"Enter three grades ";
cin >>
one >> two >> three;
return
(float(one+two+three) / 3.0);
// the
total of three grades are first converted to
float
}
|
Program Run
3-1
| Enter three grades 88 44 99
Three grades
are: 88 44 99
The average is
: 77
Student passed
the course!
|
The decision was made
using the if-else statements:
if (average >= 70) cout <<
"Student passed the course!";< /FONT>< /FONT>< /FONT>
else cout <<
"Student failed the course!";
We could add compound
statements under the if condition or the else condition or both like
this:
if (average >= 70)</FONT><
/FONT>< /FONT>
{
cout <<
"Student Passed the Course!\n";
cout << "The
student is allowed to take the next course.";
}
else
{
cout <<
"Student failed the course!\n";
cout << "This
course must be repeated before taking the next course!";
}
The operator symbols we used here >=
are called Relational Operators. Relational operators are ==
(equal to), > (greater than), < (less than), != (not equal
to), >= (greater than or equal to), and <= (less than or equal
to). The result of a relational operation is either false
or true. Variables that hold false or true are
called bool variables.
There were only two
alternatives in the above situation, either passed or failed. In
actual grading we want to go beyond pass/fail; we want to assign a
letter grade of A, B, C, D, or F. Let us rewrite the above program
to handle the multiple alternatives. See Program 3-2.
Program
3-2.
| ******************************************
Accept three grades, find the
average
and display the letter
grade.
Teaching objective - multiple
alternatives
By Dr. John Abraham
Created for 1380 students
*****************************************/
#include <iostream.h>
#include <iomanip.h> //to format
input and output.
//Here setw and endl require
it
float findave (int &, int &,
int &);
char getgrade(int);
int main ()
{
int one, two, three;
float average;
char grade;
average= findave (one, two,
three);
cout << "Three grades are: "
<<one <<setw(4)<<two
<<setw(4)<<three <<endl;
//endl inserts line feed and carriage
return
cout << "The average is : "
<<average <<endl;
grade = getgrade(average);
cout << "The letter grade is :
"<< grade << "\n";
getchar ();
}
float findave(int &one, int
&two, int &three)
{
cout << "Enter three grades
";
cin >> one >> two >>
three;
return (float(one+two+three) /
3.0);
// the total of three grades are first
converted to float
}
char getgrade (int average)
{
if (average >=90)return
('A');
else if (average>= 80)
return('B');
else if (average >=70) return
('C');
else if (average >= 60) return
('D');
else return('F');
} |
In the getgrade function if the average is
90 or above the function returns an A and ends the function; it only
continues if the average is not 90 or above. You may want to modify
the program as follows to avoid many return statements. The
program reads better when you only have one
return.
char getgrade (int average)
{
char grade;
if (average >=90) grade = . A. ;
else if (average>= 80) grade =
'B';
else if (average >=70) grade
='C';
else if (average >= 60) grade
='D';
else grade ='F';
return (grade);
}
Program Run 3-2.
| Enter
three grades 90 93 89
Three grades are: 90 93 89
The average is : 90.6667
The letter grade is : A
Enter three grades 66 58 52
Three grades are: 66 58 52
The average is : 58.6667
The letter grade is : F
Enter three grades 77 82 75
Three grades are: 77 82 75
The average is : 78
The letter grade is :
C |
Any time you write a
program for multiple alternatives, the program should be run to
check every alternative. In program Run 3-2 only three alternatives
are tested. If you were to turn this program in for a grade, you
should include all the alternatives.
Logical operators
work with boolean values or results of
relational operations. Logical operators are: AND
(&&), OR (||), and NOT (!). For each of
this operation we can obtain a truth
table.
T && T => T T || T = > T !T =
> F
T && F => F T || F = > T !F =
>T
F && F => F F || F =
>
Suppose the average
score is 95. Let us try this statement:
If (average >=90 && average <=
100)
cout << "Your grade is A
\n";
The first relational
operation of average >= 90 yields a
T.
The second operation of average <=
100 also yields a T. T && T
gives a T. Since the entire operation yields a true then "Your grade
is A" is displayed. If, on the other hand, the average score is
88, the first operation will yield a false and the second operation
will yield a true (88 is less than 100); F && T is False,
and the output will not be displayed. The concept of logical and
relational operators will become more clear in the next
chapter when we deal with repetitions.< /FONT><
/FONT>
Suppose you created a
menu to choose one of the items from a list you may have to write
some thing like this:
If (choice== 1)AddClient ();< /FONT>
else
if (choice == 2) EditClientInfo ();
else if (choice==
3)LookUpClient();
and so
on&
If the menu has many items there is a
lot of coding you have to do and the code is hard to follow. There
is alternative to the multiple if/else statements. We can use the
switch statement as shown
below.
Switch
(choice)
{ case 1:
AddClient();
break;
case 2:
EditClientInfo();
break;
case 3:
LookUpCleint();
break;
and so on..
default :
cout <<
"invalid response";
}
We are essentially
telling c++ to do something in case of choice is 1, 2, or 3 and so
on. If a match is not found then it falls to the default and carries
out that instruction. You need to remember that you cannot use any
relational operators with the case statement such as case >3.
What happens if you do not include the break statements? Every case
statement will be executed until it finds the break statement or
until the end of the block. Try deleting the break statements
and see what happens.
Here is a complete
example of a program. Let us write a program to recieve three
grades, find its average, determine the letter grade and write a
brief comment about the grade.
|
Program Three-3
/******************************************
Accept three grades,
find the average
and display the
letter grade.
Teaching objective -
multiple alternatives
By Dr. John Abraham
Created for 1380
students
*****************************************/
#include
<iostream.h>
#include
<iomanip.h> //to format input and output.
//Here setw and endl
require it
float findave (int
&, int &, int &);
char
getLetterGrade(int);
void Message(int,
int, int, float, char);
int main ()
{
int one, two, three;
float average;
char grade;
average= findave
(one, two, three);
grade =
getLetterGrade(average);
Message (one, two,
three, average, grade);
return 0;
}
float findave(int
&one, int &two, int &three)
{
cout << "Enter
three grades ";
cin >> one
>> two >> three;
return
(float(one+two+three) / float(3.0));
// first
converted to float to avoid warning
}
char getLetterGrade
(float average)
{
char grade;
if (average >= 90) grade=
'A';
else if (average>= 80) grade=
'B'; <
/FONT>
else if (average >= 70) grade=
'C';
else if (average >= 60) grade=
'D'; <
/FONT>
else grade = 'F';
return (grade);
}
void Message (int
one, int two, int three, float average, char grade)
{
cout << "Three
grades are: " <<one <<setw(4)<<two
<<setw(4)<<three <<endl;
cout << "The
average is : " <<average <<endl;
cout << "\nThe
letter grade is : "<< grade << endl;
switch (grade)
{
case 'A' : cout
<< "Very impressive grade indeed!\n";break;
case 'B' : cout
<< "A solid performance, congratulations!\n"; break;
case 'C' : cout
<< "C++ is a tough course, but YOU MADE IT!\n";break;
case 'D' : cout
<< "Made it eh? \n";break;
case 'F' : cout
<< "Don't give up. Try keeping up with all the
homework!\n";
}
}
|
|
Program Run Three-3
Enter three grades 80 85 99
Three grades are: 80 85 99
The average is : 88
The letter grade is : B
A solid performance,
congratulations!
Press any key to
continue |
Assignment
Write a program to display the name of the
month, given its number. For example if you enter 4 for the month,
it should display April. Write it using if/else and then modify it
to use the case statement.
Include Files
:
Many programmers use same functions or code
segments repeatedly in many of the programs they write. For example,
you have been writing the same code to prepare a printer file every
time you write a program. It would be convenient if we were able to
save the necessary code to open and close a printer file so that we
can use it with every program we write. In fact, C++ provides such a
convenience through the include files.
To write a header file, launch the Visual C++
and choose to create a new file. From the Files Tab choose C++
header file. Write the code as shown in Program 5-1 and save it as
printer.h file.
Program 5-1
| /****************************
Include file for Printer output
Provided by Dr. John Abraham
For CSCI 1380 students
****************************/
#include <fstream.h>
ofstream printer;
void openPrinter()
{
char string[20];
cout <<"Enter name of the printer
file-> ";
cin >>string;
printer.open(string);
}
void closePrinter()
{
printer.close();
}
|
Once the header file is saved, you can include
these files in any future programs you write. Let us modify the
program we wrote in the previous chapter. Write the cpp program as
it appears in Program 5-2. Compile and run the program.
Program 5-2
| /******************************************
Display 1 to 100 on the screen
and send the output to a file.
Teaching objective - include
files.
By Dr. John Abraham
Created for 1380 students
*****************************************/
#include <iostream.h>
#include <c:\tempc\printer.h>
//substitute with your file name
int main()
{
openPrinter(); //call function from
printer.h
int number;
number = 1;
while (number <= 100)
{
cout << number << " ";
//display number and put some spaces
printer << number << "\n";
number ++; //increment number by
one
}
return (0);
closePrinter();
} |
Go to top of this chapter
|
