C++ Programming Basics
Chapter 2 Lecture
CSIS 10A
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Agenda
Review 
An Intermediate Program
Making a Program Interactive
Assignment Statements
Standard Program Structure
File output
Debugging
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Review –what does this show?
int x, y;
x = 8; y = 6;
cout << x << y;
cout << x << " " <<
y;
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Review –Identify each piece
#include <iostream>
using namespace std;
int main()
{
// this program stores data in a variable
int m;
cout << “Enter the value of m:”;
cin >> m;
cout << “m = “ << m << endl;
system(“pause”);
return 0;
}
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Variables and Assignments
Variables are like small blackboards
We can write a number on them
We can change the number
We can erase the number
C++ variables are names for memory locations
We can write a value in them
We can change the value stored there
We cannot erase the memory location
•
Some value is always there
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Review –what does this show?
int x;
x=6;
x=8;
cout << "x = " << x;
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Identifiers
Variable names are called identifiers
Choosing variable names
Use meaningful names that represent data to be
stored
First character must be
• a letter
• the underscore character
_
Remaining characters must be
• letters
• Numbers
• underscore character
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Which identifiers are legal?
feet
1993tax
Sum
Valid?
FINAL
final
Average score
Average_score
Average.score
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Keywords
Keywords (also called reserved words)
Are used by the C++ language
Must be used as they are defined in
the programming language
Cannot be used as identifiers
Examples (75 altogether):
• main, while, if, new, for, do, class, struct, cin, cout
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Declaring Variables
Before use, variables must be declared
Tells the compiler the type of data to store
Examples: int one_weight, total_weight;
int represents whole numbers
• Could store 1, 4, -345, etc.
• one_weight and total_weight are both of type int
• Many other types, but for now, just use int!!!
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Declaring Variables (Part 2)
Put all your variable declarations at the
top of main
int main()
{

int score1, score2, sum;
cin>>
… etc …
sum=score1+score2;
… etc …
return 0;
}
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Declaring Variables (Part 3)
Declaration syntax:
Type_name Variable_1 , Variable_2, . . . ;
Declaration Examples:
int m_score, total_score;
float moon_distance;
int age, num_students;
char grade;
ONLY USE TYPE int FOR NOW!!!
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Agenda
Review
An Intermediate Program 
Making a Program Interactive
Arithmetic
Standard Program Structure
Debugging
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An intermediate C++ program:
// height.cpp
// Convert height in feet to inches.
#include <iostream>
using namespace std;
int main()
{
int feet, inches;
feet = 6;
inches = feet * 12;
cout << "Height is " << inches << " in.";
return 0;
}
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Execution – what you see
Height is 72 in.
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Execution – what really happens
int feet, inches;
feet
?
int
inches
?
int
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Execution – what really happens
feet=6;
feet
6
int
inches
?
int
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Execution – what really happens
inches = feet * 12;
feet
6.0
int
6*12
inches
72
int
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Execution – what really happens
cout << "Height is " << inches << " in.";
feet
6.0
int
inches
Height is 72 in.
72
int
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Agenda
Review
An Intermediate Program
Making a Program Interactive 
Arithmetic
Standard Program Structure
Debugging
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Interactive Program
The previous program always runs exactly the same
way (Height is 72 in)
We’d like to be able to “put in” the data we want to
process
So we add two more lines. One asking for data:
cout<<“What is height in feet?”<<endl;
The other takes input:
cin >> feet;
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An intermediate C++ program:
// height.cpp
// Convert height in feet to inches.
#include <iostream>
using namespace std;
int main()
{
int feet, inches;
cout << “What is height in feet?” << endl; //********
cin >> feet;
//********
inches = feet * 12;
cout << "Height is " << inches << " in.";
return 0;
}
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Basic Interactive Program
int main()
{
1) Declare Variables
2) Ask (prompt) for data
3) Input data
4) Calculate result
5) Display result with message
return 0;
}
Go back a slide and number the lines
Then run height.cpp and make interactive
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Agenda
Review
An Intermediate Program
Making a Program Interactive
Arithmetic 
Standard Program Structure
Debugging
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Assignment Statements
An assignment statement changes the value of a variable
total_weight = one_weight + number_of_bars;
• total_weight is set to the sum one_weight + number_of_bars
Assignment statements end with a semi-colon
The single variable to be changed is always on the left
of the assignment operator ‘=‘
On the right of the assignment operator can be
• Constants -- age = 21;
• Variables -- my_cost = your_cost;
• Expressions -- area = length * width;
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Assignment Statements and Algebra
The ‘=‘ operator in C++ is not an equal sign
The following statement cannot be true in algebra
number_of_bars = number_of_bars + 3;
In C++ it means the new value of number_of_bars
is the previous value of number_of_bars plus 3
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Initializing Variables
Declaring a variable does not give it a value
Giving a variable its first value is initializing the
variable
Variables are initialized in assignment statements
int miles, area;
// declare the variables
miles = 26;
// initialize the variable
area=0;
// initialize
Declaration and initialization can be combined
int miles = 26, area = 0.0;
Variables that are going to be input using cin>>
or calculated later do not need to be initialized
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Arithmetic in C++
Basic operations + - *
A = pr2
F = (v -a)
(v+a)
/
area=radius*radius*3.14;
force=(v-a)/(v+a);
More on arithmetic later. C++ has some
interesting properties to be explored next
chapter.
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Can you guess what is stored in x?
int a, b=3, c, x;
a=b*2;
c=a+3;
x=c-2;
a
b
c
x
?
3
?
?
6
3
?
?
6
3
9
?
6
3
9
7
Program flow is sequential (top to bottom)
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Your turn…what is stored in x?
a
b
c
x
int a, b, c, x=3;
a=2;
x=3+a;
x=x+a;
Program flow is sequential, order matters!!
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Agenda
Review
An Intermediate Program
Arithmetic
Standard Program Structure 
Debugging
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Standard Program Structure
To solve most problems, your main() program
will generally look like this (conceptually)
1. Declare variables for input, result and
intermediate data
2. Ask for data
3. Input data (cin)
4. Calculate result
5. Output result (cout)
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Another interactive C++ program:
// cents2.cpp
// Convert input number of nickels and dimes
// to cents.
#include <iostream>
using namespace std;
Notice cascading input
int main()
{
int nickels, dimes, cents;
cout << "Enter number of nickels and dimes: ";
cin >> nickels >> dimes;
cents = 5 * nickels + 10 * dimes;
cout << nickels << " nickels and "
<< dimes << " dimes " << "= "
<< cents << " cents " << endl;
return 0;
}
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Your Turn
Run cents2.cpp and verify it works correctly
Read p32 – 33 to see how to make the
program write output to a file
Modify the program to input dimes and
quarters and calculate the equivalent cents
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Agenda
Review
An Intermediate Program
Arithmetic
Standard Program Structure
Debugging 
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Syntax Errors
// errors.cpp
#include <iostream>
using namespace std;
This program has 3 errors
Run it and see what they are
int main()
{
int n;
cout << "Hello" << endl;
N = 2;
cout << "n eqalls " << n
cout << "So long << endl;
system("pause");
return 0;
}
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Tracking them down
Syntax—
double click on the first error message
it takes you to that line of code
Look at or above that line for possible errors
Fix it and try again
Errors often create other errors
Just fix the first one, then recompile
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That’s a wrap !
What we learned today:
How to write an intermediate C++ program
Standard program structure
Assignments and Basic Arithmetic
How to debug your program
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Go back home proud !
You’re a C++ programmer !
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