This presentation is a part of the COP2272C college level course taught at the Florida Polytechnic University located in Lakeland Florida. The purpose of this course is to introduce students to the C++ language and the fundamentals of object orientated programming.. The course is one semester in length and meets for 2 hours twice a week. The Instructor is Dr. Jim Anderson.

1. An Introduction To Software
Development Using C++
Class #18:
Vectors & Arrays

2. Problems With Your Homework #2
“No hardcoding of a solution is permitted. Your program should be able to be
run for any amount of time (e.g. two days) and produce the correct output
for the entire time.”

3. Thoughts On Homework #3:
A Lot Of Subroutine Calls
Return Addresses
North
South
West East
Main0
1
2
3
4
5
6
7
8
9
10
11
North
South
West
East
North
South
West
East
North
South
West
Solution? Exit

4. Thoughts On Homework #3:
When To End?
North
South
West East
class Stoplight
{
private:
startTime = time(0);
}
If (time(0) – startTime >= 60)
exit;

5. Thoughts On Homework #3:
How To Handle The Emergency Vehicle
North
South
West East
1. East is processing when
the emergency vehicle
arrives.
2. East passes control to West.
3. West commands everyone
else to go to red and it goes
to green.
4. West processes the emergency
vehicle and then resumes
normal operation.

6. A Common Problem
• A common problem in programming is not
knowing how many of something you have while
you’re writing a program – happens a lot.
• The Standard C++ Library has a ready-made
solution: the standard container classes. The
container classes are one of the real
powerhouses of Standard C++.
Image Credit: drvidyahattangadi.com

7. Say Hello To Vectors
• A vector is a collection of objects, all of which
have the same type.
• Every object in the collection has an
associated index, which gives access to that
object.
• A vector is often referred to as a container
because it “contains” other objects.
Image Credit: play.google.com

8. How Do We Use Vectors?
• To use a vector, we must include the
appropriate header.
#include <vector>
Image Credit: sivers.org

9. Introducing Vectors
• The vector class is a template, which means that it can be
efficiently applied to different types.
• That is, we can create a vector of shapes, a vector of dogs, a vector of
strings, etc.
• Basically, with a template you can create a “class of anything.”
• To tell the compiler what it is that the class will work with (in this case,
what the vector will hold), you put the name of the desired type in “angle
brackets,” which means ‘<’ and ‘>’.
• So a vector of string would be denoted vector<string>. When you do this,
you end up with a customized vector that will hold only string objects, and
you’ll get an error message from the compiler if you try to put anything
else into it.
Image Credit: http://www.viralnova.com/crazy-xray-photos/3/

10. All About Templates
• A vector is a class template.
• C++ has both class and function templates.
• Templates are not themselves functions or classes.
• Instead, they can be thought of as instructions to the compiler for
generating classes or functions.
• The process that the compiler uses to create classes or functions
from templates is called instantiation.
• When we use a template, we specify what kind of class or function
we want the compiler to instantiate.
Image Credit: www.digital-builder.co.uk

11. How To Initialize A Vector
vector<int> v1(10); // v1 has ten elements with value 0
vector<int> v2{10}; // v2 has one element with value 10
vector<int> v3(10, 1); // v3 has ten elements with value 1
vector<int> v4{10, 1}; // v4 has two elements with values 10 and 1
Image Credit: support.radioshack.com

12. How To Initialize A Vector
• We can usually omit the value and supply only a size.
• In this case the library creates a value-initialized element initializer for us.
This library-generated value is used to initialize each element in the
container.
• The value of the element initializer depends on the type of the elements
stored in the vector.
• If the vector holds elements of a built-in type, such as int, then the
element initializer has a value of 0. If the elements are of a class type, such
as string, then the element initializer is itself default initialized:
vector<int> ivec(10); // ten elements, each initialized to 0
vector<string> svec(10); // ten elements, each an empty string
Image Credit: www.youtube.com

13. Adding Things To A Vector
• Since vector expresses the concept of a “container,” there must be a way
to put things into the container and get things back out of the container.
• To add a brand-new element on the end of a vector, you use the member
function push_back( ).
• The. reason the name of this member function might seem a bit verbose
– push_back( ) instead of something simpler like “put” – is because
there are other containers and other member functions for putting
new elements into containers.
• For example, there is an insert( ) member function to put something in the
middle of a container.
• There’s also a push_front( ) (not part of vector) to put
things at the beginning.
Image Credit: blogs.courier-journal.com

14. How Do You Get Things
Out Of A Vector?
• So you can put new elements into a vector with push_back( ), but
how do you get these elements back out again? We make the vector look like an array.
• The array is a data type that is available in virtually every programming language so you
should already be somewhat familiar with it.
• Arrays are aggregates, which mean they consist of a number of elements clumped together.
The distinguishing characteristic of an array is that these elements are the same size and are
arranged to be one right after the other.
• Most importantly, these elements can be selected by “indexing,” which means you can say “I
want element number n” and that element will be produced, usually quickly.
• Although there are exceptions in programming languages, the indexing is normally achieved
using square brackets, so if you have an array a and you want to produce element five, you
say a[4] (note that indexing always starts at zero).
• This very compact and powerful indexing notation is incorporated into the vector.
Image Credit: www.dynafile.com

15. Sample Program:
Print Out File With Line Numbers// File Fillvector.cpp
// Copy an entire file into a vector of string
#include <string>
#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
int main()
vector<string> v;
ifstream in("18 Class 01 Fillvector.cpp");
string line;
while(getline(in, line))
v.push_back(line); // Add the line to the end
// Add line numbers:
for(int i = 0; i < v.size(); i++)
cout << i << ": " << v[i] << endl;
}
0: // File Fillvector.cpp
1: // Copy an entire file into a vector of string
2:
3: #include <string>
4: #include <iostream>
5: #include <fstream>
6: #include <vector>
7:
8: #include <unistd.h>
9: #include <string.h>
10:
11: using namespace std;
12:
13: int main(){
14:
15: vector<string> v;
16:
17: ifstream in("18 Class 01 Fillvector.cpp");
18: string line;
19:
20: while(getline(in, line))
21: v.push_back(line); // Add the line to the end
22:
23: // Add line numbers:
24: for(int i = 0; i < v.size(); i++)
25: cout << i << ": " << v[i] << endl;
26:
27: }
stringobjects are pushed
onto the back of the
vector v
Once the while
loop completes,
the entire file is
resident in
memory, inside
v
1

16. Sample Program:
Place Integers Into A Vector
// File:Intvector.cpp
// Creating a vector that holds integers
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> v;
for(int i = 0; i < 10; i++)
v.push_back(i);
for(int i = 0; i < v.size(); i++)
cout << v[i] << ", ";
cout << endl;
for(int i = 0; i < v.size(); i++)
v[i] = v[i] * 10; // Assignment
for(int i = 0; i < v.size(); i++)
cout << v[i] << ", ";
cout << endl;
} // end of main
0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
0, 10, 20, 30, 40, 50, 60, 70, 80, 90,
You also have the ability to assign (and thus
to change) to any element of a vector, also through
the use of the square-brackets indexing operator.
2

17. Vector In-Class
Programming Assignment
• Create a vector<float> and put 25 floating-point numbers
into it using a for loop.
– Display the vector.
• Create three vector<float> objects and fill the first two as
in the previous exercise.
– Write a for loop that adds each corresponding element in the first two vectors
and puts the result in the corresponding element of the third vector.
– Display all three vectors.
• Create a vector<float> and put 25 numbers into it as in
the previous exercises.
– Now square each number and put the result back into the same location in
the vector.
– Display the vector before and after the multiplication.
Image Credit: blog.intellisource.com

18. Arrays
• An array is a consecutive group of memory locations that all have the same type.
• To refer to a particular location or element in the array, we specify the name of the array and the position number
of the particular element in the array.
• This figure shows an integer array called
c that contains 12 elements. You refer to
any one of these elements by giving the
array name followed by the particular
element’s position number in square
brackets ([]).
• The position number is more formally called a
subscript or index (this number specifies the
number of elements from the beginning of
the array).
• The first element has subscript 0 (zero) [zero indexing]
• Thus, the elements of array c are c[0]
(pronounced “c sub zero”), c[1], c[2] and so on.
• The highest subscript in array c is 11, which is 1 less than the number of elements in the array (12). Array names
follow the same conventions as other variable names.

19. Arrays
• A subscript must be an integer or integer expression
(using any integral type).
• If a program uses an expression as a subscript, then the program
evaluates the expression to determine the subscript.
• Example, if we assume that variable a is equal to 5 and that variable
b is equal to 6, then the statement:
adds 2 to array element c[11].
• A subscripted array name is an lvalue—it can
be used on the left side of an assignment, just
as nonarray variable names can.
c[ a + b ] += 2;
Image Credit: learningideasgradesk-8.blogspot.com

20. How To Declare An Array
• Arrays occupy space in memory.
• To specify the type of the elements and
the number of elements required by an
array use a declaration of the form:
type arrayName[ arraySize ];
• The compiler reserves the appropriate amount of memory. (Recall that a
declaration which reserves memory is more properly known as a
definition.)
• The arraySize must be an integer constant greater than zero. For example,
to tell the compiler to reserve 12 elements for integer array c, use the
declaration:
int c[ 12 ]; // c is an array of 12 integers
Image Credit: www.scholastic.com

21. How To Use An Array
• Array access is extremely fast.
• However, if you index past the
end of the array, there is no
safety net – you’ll step on
other variables.
• The other drawback is that you
must define the size of the
array at compile time; if you
want to change the size at
runtime you can’t
do it.
a[0] = 0
a[1] = 10
a[2] = 20
a[3] = 30
a[4] = 40
a[5] = 50
a[6] = 60
a[7] = 70
a[8] = 80
a[9] = 90
// File: Arrays.cpp
#include <iostream>
using namespace std;
int main() {
int a[10];
for(int i = 0; i < 10; i++) {
a[i] = i * 10;
cout << "a[" << i << "] = "
<< a[i] << endl;
}
}

22. In Class Programming Challenge:
Seal Team 6 & Lakeland
• You are part of a Seal team that has been ordered to
go into zombie infested Lakeland and rescue a group
of doctors at the hospital.
• Lakeland is represented by a 20 x 20 two dimensional
table that I have provided you with.
• You are to write a program that will enter the Lakeland at location (19,0) (lower left-
hand corner), work your way to the center to rescue the doctors, and then work your
way out through the exit located at (0,0). You are to avoid all contact with zombies.
Always move forward, never move behind you. Stop when you reach the extraction
point.
• A “cell” in the table that is infested with zombies contains a “1”. A clear cell has a “0”. A
cell with the doctors has an “8”.
• Every time your Seal team makes a move, print out the entire two dimensional table
and show me where you are at by marking that cell with an “-”.

23. What’s In Your C++ Toolbox?
cout / cin #include if/else/
Switch
Math Class String getline While
For do…While Break /
Continue
Arrays