Chapter
1
Introduction
Chapter 2
Functions
Chapter 3
Branching
Chapter 4
Iteration
Chapter 5
OOP
Chapter 6
Arrays
|
CHAPTER 4
( Iteration )
1 ) Iteration
2 ) More On Loops
3 ) Numeric Data Types and
formatting
Suppose
you want to display numbers 1 to 100 on the screen.
Based on what we studies so far, you will have to write one
hundred cout statements. If you think about, all you are doing
is adding one to the previous number and displaying it
over and over again until 100 has been displayed. Let us
write the steps to do it.
Number gets 1.
Display the number
Add one to it
Repeat these two statements.
Stop when 100 has been displayed.
Let us rework it.
Number = 1
Do the following statements (in brackets) while number less
than or equal to 100.
{
display number
add one to number
}
|
Here are the steps:
- Initialize the variable (this variable is also called
the loop control variable or LCV), because this variable
controls the loop. In this example the LCV is
number.
- Check for the condition to enter the loop.
The condition should yield a True to enter the loop. If the
condition yields a false, the loop is not entered.
- Set up the body of the loop. You may have one or
multiple things to do within the loop body. The body here
appears within the brackets.
- Change the value of the LCV within the body.
In this example
the number is changed by adding a one to
it.
These steps will work in all programming
languages. Let us write this program in c++. See program 4-1.
Program
4-1
|
/******************************************
Display 1 to
100 on the screen
Teaching
objective - while loop
By Dr. John
Abraham
Created for
1380 students
*****************************************/
#include
<iostream.h>
int
main()
{
int
number;
number =
1;
while (number
<= 100)
{
cout <<
number << " "; //display number and put some
spaces
number ++;
//increment number by one
}
getchar();
return
(0);
}
|
Program Run
4-1
|
1 2 3 4 5 6 7
8 9 10 11 12 13 14 15 16 17 18
19 20 21 22 23
24 25 26 27 28 29 30 31 32 33 34
35 36 37 38 39
40 41 42 43 44 45 46 47 48 49 50
51 52 53 54 55
56 57 58 59 60 61 62 63 64 65 66
67 68 69 70 71
72 73 74 75 76 77 78 79 80 81 82
83 84 85 86 87
88 89 90 91 92 93 94 95 96 97 98
99
100 |
This while loop is a count controlled loop, since we
wanted to repeat the loop a certain number of times. The count
controlled loop may also be referred to as a step controlled
loop. We can write a sentinel controlled loop as well.
A sentinel value is a value that
belongs to a type but does not belong to the set you are working
with. For example suppose you are entering names. Names belong a
type called string. When asked for the name what if you entered .
quit. ?. . Quit. also belongs to the string type, however, does not
belong to the set of names. Parents do not name a child Quit! Let me
illustrate it with Program 3-2.
Program
4-2
|
/******************************************
Accept and
display names
Teaching
objective - while loop/sentinel controlled
By Dr. John
Abraham
Created for
1380 students
*****************************************/
#include
<iostream.h>
#include
<string.h>
int
main()
{
string
name;
cout <<
"Enter a name ";
cin >>
name;
while (name
!= "quit")
{
cout <<
"Hello, " << name <<"\n";
cout <<
"Enter another name or type 'quit' to exit ";
cin >>
name ;
}
getchar();
return
(0);
} |
Program Run
4-2
|
Enter a name
Randy
Hello,
Randy
Enter another
name or type 'quit' to exit Sandy
Hello,
Sandy
Enter another
name or type 'quit' to exit James
Hello,
James
Enter another
name or type 'quit' to exit Roger
Hello,
Roger
Enter another
name or type 'quit' to exit Jill
Hello,
Jill
Enter another
name or type 'quit' to exit
quit |
WARNING:
The above program
does work with Borland compiler, not with Visual C++. If you
wish to run this program with the visual compiler make the following
modifications:
/******************************************
Accept and display names
Teaching objective - while loop/sentinel controlled
By Dr. John Abraham
Created for 1380
students
*****************************************/
#include <iostream.h>
include <string.h>
int main()
{
char name[20];
cout << "Enter a name ";
cin >> name;
while (strcmp (name, "quit")
!=0)
{
cout << "Hello, "
<< name <<"\n";
cout <<
"Enter another name or type 'quit' to exit ";
cin >> name ;
}
return (0);
}
What if you wanted
to keep accepting names until . quit. is entered, but do not want to
accept more than 5 names? To do this we will make some modifications
to the Program 4-2. First, we will change the test to include if the
number of names is less than or equal to 5. Second we will increment
a counter when a name is entered. See program 4-2A.
Program
4-2A
|
/***************************************************************
Accept and
display names
Teaching
objective - while loop/sentinel and count ontrolled
By Dr. John
Abraham
Created for
1380 students
*****************************************************************/
#include
<iostream.h>
#include
<string.h> //to handle string functions.
int
main()
{
string
name;
int
count;
count =
1;
cout <<
"Enter a nameà ";
cin >>
name;
while (name !="quit" && count
<= 5)
{
count
++;
cout <<
"Hello, " << name <<"\n";
cout <<
"Enter another name or type 'quit' to exità ";
cin >>
name ;
}
count --;
//actual number of names entered is count minus 1.
cout <<
count << " names were entered " << "\n";
getchar();
return
(0);
} |
|
Enter a
name--> James
Hello,
James
Enter another
name or type 'quit' to exit--> Mary
Hello,
Mary
Enter another
name or type 'quit' to exit--> Rose
Hello,
Rose
Enter another
name or type 'quit' to exit--> quit
3 names were
entered
Enter a
name--> Jack
Hello,
Jack
Enter another
name or type 'quit' to exit--> Jill
Hello,
Jill
Enter another
name or type 'quit' to exit--> Roger
Hello,
Roger
Enter another
name or type 'quit' to exit--> Ed
Hello,
Ed
Enter another
name or type 'quit' to exit--> Sandy
Hello,
Sandy
Enter another
name or type 'quit' to exit--> Reg
5 names were
entered |
While loop is a pre-test loop. It tests for the condition before
entering the loop. We will be discussing a loop structure that
checks for the condition at the bottom of the loop. If you want to
use a pre-test loop controlled by a counter as seen in Program 4-1,
you could either use a while loop or a for loop. For
loop is variation of while loop
specifically designed for count controlled loop. Program 4-3 is a
modification of Program 4-1; the while loop has been changed to a
for loop.
Program
4-3
|
/******************************************
Display 1 to
100 on the screen
Teaching
objective - For loop
By Dr. John
Abraham
Created for
1380 students
*****************************************/
#include
<iostream.h>
int
main()
{
int
number;
for (number =1; number <
= 100; number++)
{
cout <<
number << " "; //display number and put some
spaces
}
getchar();
return
(0);
} |
Program Run
4-3
|
1 2 3 4 5 6 7
8 9 10 11 12 13 14 15 16 17 18
19 20 21 22 23
24 25 26 27 28 29 30 31 32 33 34
35 36 37 38 39
40 41 42 43 44 45 46 47 48 49 50
51 52 53 54 55
56 57 58 59 60 61 62 63 64 65 66
67 68 69 70 71
72 73 74 75 76 77 78 79 80 81 82
83 84 85 86 87
88 89 90 91 92 93 94 95 96 97 98
99
100 |
As you can see, the Program Run 4-3
looks identical to Program Run 4-1. Let us understand this
statement: for (number =
1; number < =
100;
number++). The values
of the variable number are given, the initial value, loop execution
condition, and the step value. In Program 4-3A, we will change all three values
and see how the execution changes. < /FONT> <
/FONT>
Program
4-3A
|
/*************************************************************
Display all
even numbers beginning with 2 and ending with 100
Teaching
objective - For loop
By Dr. John
Abraham
Created for
1380 students
**************************************************************/
#include
<iostream.h>
int
main()
{
int
number;
for (number =2; number < = 100; number
= number+2)< /FONT>< /FONT>
{
cout <<
number << " "; //display number and put some
spaces
}
getchar();
return
(0);
} |
Program Run
4-3A
|
2 4 6 8 10 12
14 16 18 20 22 24 26 28 30 32 34
36 38 40 42 44
46 48 50 52 54 56 58 60 62 64 66
68 70 72 74 76
78 80 82 84 86 88 90 92 94 96
98 |
We could modify this
program to display the number backwards. See Program 4-3B. Note how
the initial variable, loop execution condition, and the step values
are changed.
Program
4-3B
|
/*************************************************************
Display all
even numbers backward beginning with 100 and ending with
2
Teaching
objective - For loop
By Dr. John
Abraham
Created for
1380 students
**************************************************************/
#include
<iostream.h>
int
main()
{
int
number;
for (number =100; number > = 1; number = number-2)<
/FONT>< /FONT>< /FONT>< /FONT>
{
cout <<
number << " "; //display number and put some
spaces
}
getchar();
return
(0);
}
|
Suppose you want to find the average grades for 20 students in a
class on a quiz. You could either use the while loop or the for
loop. However, if you want to write this program for a more general
situation in which the number of students vary in different classes,
you will have to use a sentinel controlled while loop. The
sentinel value could be . 99 for the grade input. Program 4-4
illustrates this.
Program
4-4
|
/*************************************************************
Find average
of a set of exam scores
Teaching
objective - Sentinel controlled while loop
By Dr. John
Abraham
Created for
1380 students
**************************************************************/
#include
<iostream.h>
int
main()
{
int grade,
total, count, average; //count will keep track of number of
grades
count = 1; //
initialize both count and total
total =
0;
cout <<
"Enter a grade or -99 to quit--> ";
cin >>
grade;
while (grade != -99)<
/FONT>< /FONT>
{
total += grade;<
/FONT>< /FONT>
count
++;
cout <<
"Enter a grade or -99 to quit--> ";
cin >>
grade;
}
count--;
average =
total/count;
cout <<
"Sum of " << count << " grades entered ---> "
<< total << "\n";
cout <<
"The average grade is ---> " << average;
getchar();
return
(0);
} |
Program Run
4-4
|
Enter a grade
or -99 to quit--> 100
Enter a grade
or -99 to quit--> 88
Enter a grade
or -99 to quit--> 71
Enter a grade
or -99 to quit--> 56
Enter a grade
or -99 to quit--> 88
Enter a grade
or -99 to quit--> 65
Enter a grade
or -99 to quit--> -99
Sum of 6
grades entered ---> 468
The average
grade is ---> 78 |
We keep a running
total by initializing total to 0 and adding all grades to the
previous total. We do not want to add the . 99 to the total nor
should it count as a valid grade. The loop continuation condition
clearly states to exit the loop if a . 99 entered, therefore . 99 is
not added to the total. However, the count was already incremented,
which should be negated. This is what we do with the statement:
count--. This is a very important concept, we will be using this
quite a bit in many of the future programs.
A modification to
the above program to find average of grades is given below. Study
the subtle differences. Try running the program and entering an
invalid grade as the first grade for both programs.
*************************************************************
Find average of a
set of exam scores
Teaching objective -
Sentinel controlled while loop
By Dr. John
Abraham
Created for 1380
students
**************************************************************/
#include
<iostream.h>
int
main()
{
int grade, total= 0, count= 0;<
/FONT>< /FONT>
double average= 0.0;//count will keep track of number of
grades
< /FONT> < /FONT>
<
/FONT>
cout << "Enter a
grade (0-100) or any other number to quit --> ";
cin >>
grade;
while (grade >=0 && grade <= 100)<
/FONT>< /FONT>
{
total += grade;<
/FONT>< /FONT>
count ++;
cout << "Enter
a grade or -99 to quit--> ";
cin >>
grade;
}
if (count >0) average = total/count;< /FONT ><
/FONT >
cout << "Sum
of " << count << " grades entered ---> " <<
total << "\n";
cout << "The
average grade is ---> " << average <<endl;
return
(0);
}
The last looping
structure I want to mention is the do..while loop. Do while loop is
a post test loop; the condition is tested at the bottom of the loop.
Therefore, a do while loop will be executed at least once. Program
4-5 is a modification of the first program in this
chapter.
Program
4-4
|
/******************************************
Display 1 to
100 on the screen
Teaching
objective - do while loop
By Dr. John
Abraham
Created for
1380 students
*****************************************/
#include
<iostream.h>
int
main()
{
int
number;
number =
1;
do
{
cout <<
number << " ";
number
++;
}
while (number <=
100);<
/FONT>< /FONT>
getchar();
return
(0);
} |
Program run
4-4
|
1 2 3 4 5 6 7
8 9 10 11 12 13 14 15 16 17 18
19 20 21 22 23
24 25 26 27 28 29 30 31 32 33 34
35 36 37 38 39
40 41 42 43 44 45 46 47 48 49 50
51 52 53 54 55
56 57 58 59 60 61 62 63 64 65 66
67 68 69 70 71
72 73 74 75 76 77 78 79 80 81 82
83 84 85 86 87
88 89 90 91 92 93 94 95 96 97 98
99
100 |
More on Loops :
Suppose you already have a program and you
want to add a loop around it to make it run many times. Let us
modify a program from Chapter 3 (the grades program) to add a while
loop. First step is to decide which of the variables can be
selected as loop control variable. If no varaibles can be
selected you can add new variable - for example, a char variable -
and ask " Do you want to run the program again? ". However
this is extra work for the user to answer yes or no each time.
In the grades program we
asked for three scores, found the average and letter grade and
displayed these values. We could choose the first score as the
loop control variable. If a negative number was entered for
the first score, we can exit the while loop. Remember the
steps required for a while loop, (1) decided on a LCV; (2)
intialize the LCV; (4) setup the while loop condition; (5)
write the body of the loop; and (6) change the value of LCV within
the body of the loop.
Program 4A-1
/******************************************
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(float);
void Message(int,
int, int, float, char);
int main ()
{
int one,
two, three;
float average;
char grade;
cout <<
"This program will calculate letter grade given three scores
for any number of students.";
cout << "\n\nEnter the
first score or a negative number to quit-> "; cin >>
one;
while (one >0)
{
cout << "Enter the
second score-> "; cin >> two;
cout << "Enter
the third score-> "; cin >> three;
average=
findave (one, two, three);
grade =
getLetterGrade(average);
Message (one, two, three, average,
grade);
cout << "\n\nEnter the first score or a
negative number to quit-> "; cin >>
one;
}
return 0;
}
float findave(int one, int
two, int three)
{
float a;
a =
(float(one+two+three) / float(3.0));
//convert numbers to
float to avoid warning
return (a);
}
char
getLetterGrade (float 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);
}
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 4A-1
This program will calculate
letter grade given three scores for any number of
s
udents.
Enter the first score or a negative number
to quit-> 90
Enter the second score-> 88
Enter the
third score-> 93
Three grades are: 90 88 93
The
average is : 90.3333
The letter grade is : A
Very
impressive grade indeed!
Enter the first score or a
negative number to quit-> 78
Enter the second score->
66
Enter the third score-> 77
Three grades are: 78 66
77
The average is : 73.6667
The letter grade is :
C
C++ is a tough course, but YOU MADE IT!
Enter
the first score or a negative number to quit->
-1
|
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chapter
|
