1. Module 2 - Part 1 Variables, Assignment, and Data Types
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CSE 1321 Module 2

2. Motivation To learn the basic elements of programming:
Declaring variables (a named chunk of memory)
Data types (the kind of info you’re going to store)
Assignment (putting values into a chunk of memory)
String literals
Review printing
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CSE 1321 Module 2

3. Topics Program Structure Character Strings Variables Assignments
Constants
Primitive Data Types
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4. Program Structure
An application always contains a MAIN method so that the program can be executed.
In object-oriented programming (OOP) language, MAIN is inside a “class”
These program elements terms will be explored in detail throughout the course
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5. Comments
Comments are just notes that explain the program to yourself and others. They’re GREEN!
Block comments in Java, C++ and C#
Begin with /* and ends with */
Compiler ignores all text between /* and */
Single line comments start with //
Compiler ignores text from // to end of line
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CSE 1321 Module 2

6. Identifiers An identifier is just a name you give a variable
Rules for names:
C# and C++: Must start with a letter, can contain essentially any number of letters and digits, but no spaces, case sensitive. It cannot be keywords or reserved words – which turn blue!
Java: Must starts with a letter, an underscore (_), or a dollar sign ($). Cannot start with a digit. Cannot be a keywords (which turn blue). Can be of any length. Case sensitive.
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7. Java Keywords (bad for variable names)
abstract assert boolean break byte case catch char class const continue default do double else enum extends false final finally float for goto if implements import instanceof int interface long native new null package private protected public return short static strictfp super switch synchronized this throw throws transient true try void volatile while
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CSE 1321 Module 2

8. C# Keywords (bad for variable names)
abstract as base bool break byte case catch char checked class const continue decimal default delegate do double else enum event explicit extern false finally fixed float for foreach goto if implicit in int interface internal is lock long namespace new null object operator out override params private protected public readonly ref return sbyte sealed short sizeof stackalloc static string struct switch this throw true try typeof uint ulong unchecked unsafe ushort using var virtual void volatile while
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CSE 1321 Module 2

9. C++ Keywords
alignas, alignof, and, and_eq, asm, atomic_cancel, atomic_commit, atomic_noexcept, auto, bitand,bitor, bool, break, case, catch, char, char8_t, char16_t, char32_t, class, compl, concept, const, consteval, constexpr, const_cast, continue, co_await,co_return, co_yield, decltype, default, delete, do, double, dynamic_cast, else, enum, explicit, export, extern, false, float, for, friend, goto, if, inline, int, long, mutable, namespace, new, noexcept, not, not_eq, nullptr, operator, or, or_eq, private, protected, public, reflexpr, register, reinterpret_cast, requires, return, short, signed, sizeof, static, static_assert, static_cast, struct, switch, synchronized, template, this, thread_local, throw, true, try, typedef, typeid, typename, union, unsigned, using, virtual, void, volatile, wchar_t, while, xor, xor_eq
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CSE 1321 Module 2

10. White Space Spaces, blank lines, and tabs are called white space:
Used to separate words and symbols in a program. Extra white space is ignored
A valid program syntax can be formatted many ways
Use whitespace enhance readability, using consistent indentation
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11. Character Strings
A “string literal” contains 0 or more characters enclosed with double quotes. They turn RED.
Examples:
“The quick brown fox jumped.”
“x”
Square brackets [] can be used to access elements inside the string (later)
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12. Printing strings in Java (review)
System.out.println (“Whatever you are, be a good one.”);
System represents the Operating System
“out” is the console/screen data stream
println is a “function” to push data to the console
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13. Printing strings in C# (review)
Console.WriteLine (“Whatever you are, be a good one.”);
Console represents the Operating System’s console
WriteLine is a “function” to push data to the console
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14. Printing strings in C++ (review)
cout << “Whatever you are, be a good one.” << endl;
cout is called a stream (an output stream)
You “push” things into cout
endl is short for “end line”
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15. String Concatenation Operator (+)
String literals cannot span multiple lines
Combines string literals with other data types for printing
Example (C#):
String hello = "Hello";
String there = "there";
String greeting = hello + ' ' + there;
Console.WriteLine(greeting );
Output: Hello there
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16. Pseudocode
CLASS CountDown BEGIN METHOD Main() BEGIN s1 ← "Three... " s2 ← "Two... " s3 ← "One... " s4 ← "Zero... " PRINT(s1 + s2 + s3 + s4 + "Liftoff!") PRINTLINE()
PRINTLINE("Houston, we have a problem.") END Main END CountDown
Output:
Three... Two... One... Zero... Liftoff! Houston, we have a problem. Ps
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17. Java
// Program CountDown.java
public class CountDown { public static void main (String[] args) { String s1 = "Three... "; String s2 = "Two... "; String s3 = "One... "; String s4 = "Zero... "; System.out.println (s1 + s2 + s3 + s4 + "Liftoff!"); System.out.println ("Houston, we have a problem."); } }
Output:
Three... Two... One... Zero... Liftoff! Houston, we have a problem.
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18. C# Output: using System; class CountDown {
public static void Main(string[] args) {
string s1 = "Three... "; string s2 = "Two... "; string s3 = "One... "; string s4 = "Zero... ");
Console.WriteLine(s1 + s2 + s3 + s4 + "Liftoff!");
Console.WriteLine("Houston, we have a problem. "); }
Output:
Three... Two... One... Zero... Liftoff! Houston, we have a problem.
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19. C++ Output: cout << "One..." << "Zero...";
#include <iostream>
using namespace std;
int main() {
cout << "Three..." << "Two...";
cout << "One..." << "Zero...";
cout << "Liftoff!" << endl;
cout << "Houston, we have..." << endl;
return 0; }
Output:
Three... Two... One... Zero... Liftoff! Houston, we have a problem.
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20. Escape Sequences
Printing and escape sequence prints a special character in an output string.
Common escape sequences:
\b is backspace. (e.g “B\bsecz\bret” prints what?)
\t is tab
\n newline
\r carriage return
\” double quote
\’ single quote
\\ backslash
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21. Java
public class Roses { public static void main (String[] args) { System.out.println ("Roses are red,\n\tViolets are blue,\n"
+ "Sugar is sweet,\n\tBut I have \"commitment issues\",\n\t"
+ "So I'd rather just be friends\n\tAt this point in our "
+ "relationship."); } }
Output:
Roses are red, Violets are blue, Sugar is sweet, But I have "commitment issues", So I'd rather just be friends At this point in our relationship.
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22. C# // Escape sequences class Roses {
public static void Main(string [] args)
Console.WriteLine("Roses are red,\n\tViolets are blue,\n"
+ "Sugar is sweet,\n\tBut I have "
+ "\"commitment issues\",\n\t"
+ "So I'd rather just be friends\n\t"
+ "At this point in our relationship."); }
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23. C++
#include <iostream> using namespace std; int main() { cout << "Roses are red,\n\tViolets are blue,\n" << "Sugar is sweet,\n\tBut I have " << "\"commitment issues\",\n\t" << "So I'd rather just be friends\n\t" << "At this point in our relationship." << endl; return 0; }
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24. Variables
A variable is a name for a location in memory used to hold a data value.
A variable must be declared by specifying the variable's name and the type of information that it will hold.
Examples:
int total; // chunk of memory named total
int count, temp, result; // three variables
Multiple variables can be created in one declaration
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25. Ps Pseudocode // Prints the number of keys on a piano. CLASS PianoKeys
BEGIN
METHOD Main()
BEGIN CREATE keys ← 88
PRINT("A piano has " + keys + " keys.") END Main
END PianoKeys
Output: A piano has 88 keys. Ps
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26. Java // Prints the number of keys on a piano. public class PianoKeys {
public static void main (String[] args)
{ int keys = 88; //declare and initialize
System.out.println ("A piano has " + keys + " keys."); } }
Output: A piano has 88 keys.
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27. C#
// Prints the number of keys on a piano using System; class PianoKeys { public static void Main (string[] args) { int keys = 88; //declare and initialize Console.WriteLine("A piano has " + keys + " keys."); } Output: A piano has 88 keys.
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28. C++
#include <iostream>
using namespace std;
int main() {
int keys = 88;
cout << "A piano has " << keys << " keys." << endl;
   return 0; }
Output:
A piano has 88 keys
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29. Conventions – Naming Variables
Names of variables:
should be meaningful
reflect the data they will store.
variable names will “self document” the program
small variable names are NOT more efficient
avoid extremely long names
Avoid names similar to keywords
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30. Assignment Assignment statements change the value of a variable
The assignment operator is the = sign total = 55; // put value of 55 into total
The expression on the right is evaluated and the result is stored in the variable on the left
The value that was in total is overwritten
The data type on the right must match the data type on the left!
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31. Pseudocode
// Print the number of sides of several geometric shapes.
CLASS Geometry
BEGIN
METHOD Main()
CREATE sides ← PRINTLINE("A heptagon has " + sides + " sides.") CREATE sides ← 10
PRINTLINE("A decagon has " + sides + " sides.")
CREATE sides ← 12
PRINTLINE("A dodecagon has " + sides + " sides.")
END Main
END Geometry
Output:
A heptagon has 7 sides.
A decagon has 10 sides.
A dodecagon has 12 sides. Ps
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32. Java
// Print the number of sides of several geometric shapes. public class Geometry { public static void main (String[] args) { int sides = 7; // declare and initialize System.out.println ("A heptagon has " + sides + " sides."); sides = 10; // assignment statement System.out.println ("A decagon has " + sides + " sides."); sides = 12; // assignment statement System.out.println ("A dodecagon has " + sides + " sides."); }
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33. C#
// Print the number of sides of several geometric shapes. using System; class Geometry { public static void Main (string[] args) { int sides = 7; // declare and initialize Console.WriteLine("A heptagon has " + sides + " sides."); sides = 10; // assignment statement Console.WriteLine("A decagon has " + sides + " sides."); sides = 12; // assignment statement Console.WriteLine("A dodecagon has " + sides + " sides."); }
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34. C++
#include <iostream>
using namespace std;
int main() {
int sides = 7; // Original variable and assignment
cout << "A heptagon has " << sides << " sides" << endl;
sides = 10; // Reassign the same variable
cout << "A decagon has " << sides << " sides" << endl;
sides = 12; // Reassign the same variable
cout << "A dodecagon has " << sides << " sides" << endl;
   return 0; }
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35. Constants Values that cannot change.
A value must be assigned before the constant is used.
Three reasons:
They give meaning to otherwise unclear literal values. For example, MAX_LOAD means more than the literal 250
Program maintenance. If a constant is used in multiple places, its value need only be updated in one place.
Avoid errors by other programmers
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36. Constants – Java and C#
Use all CAPITAL LETTERS for constants and separate words with an underscore:
Java: final double TAX_RATE = .05;
C# and C++: const double TAX_RATE = .05;
C++ only: #define TAX_RATE .05
Declare constants at the top of the program
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37. Data Types Data type tells compiler: Compiler monitors use of data
How much memory to allocate
Format in which to store data
Types of operations you will perform on data
Compiler monitors use of data
C#, Java, and C++ are "strongly typed" languages. That is, variables cannot be implicitly coerced to unrelated types
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38. Data Types 8 simple data types:
4 subsets of integers
2 subsets of floating point numbers
Character
Boolean
Everything else is a complex data type, built from simple or other complex data types
Later, we’ll define our own data types!
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39. Why so many types?
Difference is in amount of memory reserved for each (i.e the size of the value stored)
A float only has 7 significant digits
Signed numbers have both positive and negative values
Unsigned numbers are >= 0
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40. Static v. Dynamic Typing
Static type checking (C#, C++ and Java)
Static type checking occurs during compilation
Requires you to declare variable types before you use them
Dynamic type checking (e.g. Python)
Dynamic type checking occurs while program is running
Does not require you to declare the data types of your variables before you use them
Python uses dynamic typing, but is also is strongly typed, as the interpreter keeps track of all variables types.
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41. Literal Numbers int testGrade = 100; byte ageInYears = 19;
Values without a decimal point are considered int
Values with decimal point are considered double, which is bigger than a float!
Examples (Java)
int testGrade = 100;
byte ageInYears = 19;
long cityPopulation = L
float salesTax = .05F; // NOTE the F
double interestRate = 0.725;
double avogadroNumber = E23;
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42. char Data Type Two common ways to hold characters:
ASCII (8 bits) – how many characters in English?
Unicode (16 bits) – how many characters in Mandarin?
Unicode is most commonly used
Example declarations:
char finalGrade = ‘A’; // NOTE single quotes
char newline, tab, doubleQuotes;
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43. boolean Data Type Two values only:
true
false
Used for decision making or as "flag" variables
Example declarations:
bool isEmpty = false; //in C# and C++
boolean passed = true; //in Java
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44. Summary
Variable declaration indicates its type and possibly its initial value.
A value is assigned using assignment operator.
A constant value doesn’t change
Data type tells how much memory to allocate, the format in which to store data, and the types of operations you will perform on data.
Primitive data types include integer, floating point, character, boolean, and decimal.
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