1. EECE.2160 ECE Application Programming
Instructor:
Dr. Michael Geiger
Fall 2018
Lecture 3:
Variables

2. ECE Application Programming: Lecture 3
Lecture outline
Announcements/reminders
Chapter 1 exercises due Monday, 9/10
Chapter 2 exercises due 9/13 & 9/15
Textbook exercises always due 3 days after related lecture—check ”Assignments” tab regularly!!!
Program 1 due Wednesday, 9/12
10 points: register for access to the course textbook
10 points: introduce yourself to your instructor
30 points: complete simple C program
Programs will also require “submission” on Blackboard
To be added by end of today
Review
Basic C program structure
Comments
Today’s lecture
Data types
Variables
6/2/2019
ECE Application Programming: Lecture 3

3. Review: Basic C program structure
Preprocessor directives
#include: typically used to specify library files
Main program
Starts with: int main() or void main()
Enclosed in block: specified by { }
Ends with return 0;
Indicates successful completion
Not used if main() is void
Basic output
Call printf(<string>);
<string> can be replaced by characters enclosed in double quotes
May include escape sequence, e.g. \n (new line)
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ECE Application Programming: Lecture 3

4. ECE Application Programming: Lecture 3
Review (cont.)
Comments
Single-line: // This is a comment
Multi-line:
/* This is also
a comment */
Typical uses
Multi-line comment at start of program with
Author’s name (& other info if appropriate)
Date started/modified
File name
Description of overall file functionality
For individual code sections
Comment for major section of code performing single function
Comment for single line of code if that line alone is important
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ECE Application Programming: Lecture 3

5. ECE Application Programming: Lecture 2
Comment example
/* ECE Application Programming Instructor: M. Geiger 6/2/2019 hello.c: Intro program to demonstrate basic C program structure and output */ #include <stdio.h> // Main program: prints basic string and exits int main() { printf("Hello World!\n"); // Comment return 0; }
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ECE Application Programming: Lecture 2

6. ECE Application Programming: Lecture 2
Representing data in C
Two major questions (for now)
What kind of data are we trying to represent?
Data types
Can the program change the data?
Constants vs. variables
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ECE Application Programming: Lecture 2

7. Four Types of Basic Data
Integer int
Floating point (single precision) float
Double Precision double
Character char
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ECE Application Programming: Lecture 2

8. ECE Application Programming: Lecture 2
Integer Constants
Any positive or negative number without a decimal point (or other illegal symbol).
Legal values:
Illegal values: 2,523 (comma) 6.5 (decimal point) $59 (dollar sign) 5. (decimal point)
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ECE Application Programming: Lecture 2

9. Range of Integers (Machine Dependent)
unsigned signed
char 0   +127
(8 bits)
short int 0   short
(16 bits)
int 0 to  long long int
(32 bits)
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ECE Application Programming: Lecture 2

10. float/double Constants
Any signed or unsigned number with a decimal point
Legal values:
Legal (exponential notation): 1.624e e e23 1.0e e e e e+7
Illegal:
$ , E5
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ECE Application Programming: Lecture 2

11. float/double Constants
Range of float (32 bits) ± E – 38 ± E + 38
Range of double (64 bits) ± E – 308 ± E + 308
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ECE Application Programming: Lecture 2

12. ECE Application Programming: Lecture 3
Character Constants
Stored in ASCII or UNICODE
Signified by single quotes (’ ’)
Valid character constants ’A’ ’B’ ’d’ ’z’ ’1’ ’2’ ’!’ ’+’ ’>’ ’?’ ’ ’ ’#’
Invalid character constants ’GEIGER’ ’\’ ’CR’ ’LF’ ’’’ ’’’’ ’”’ ”Q”
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ECE Application Programming: Lecture 3

13. Character Escape Sequences
Meaning
’\b’
Backspace
’\’’
Single quote
’\n’
Newline
’\”’
Double quote
’\t’
Tab
’\nnn’
Char with octal value nnn
’\\’
Backslash
’\xnn’
Char with hex value nn
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ECE Application Programming: Lecture 3

14. ECE Application Programming: Lecture 3
Variables
All variables have four characteristics:
A type
An address (in memory)
A value
A name
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ECE Application Programming: Lecture 3

15. ECE Application Programming: Lecture 3
Variables - name
must start with a-z, A-Z ( _ allowed, but not recommended)
other characters may be a-z, A-Z, 0-9, _
upper case/lower case are not equal (i.e. ECE, ece, Ece, EcE, eCe would be five different variables)
max length system dependent (usually at least 32)
By convention
Start with lowercase letter
Descriptive names improve code readability
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ECE Application Programming: Lecture 3

16. Variables - legal names
grossPay
carpet_Price
cArPeT_price
a_very_long_variable_name i
______strange___one_____
_ (not recommended)
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ECE Application Programming: Lecture 3

17. Variables - legal names (but not recommended)
l (that's lower case L)
O (that's capital O)
l1 (that's lower case L, and digit one)
O0Oll11 (oh,zero,oh,el,el,one,one)
_var (many system variables begin w/ _ )
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ECE Application Programming: Lecture 3

18. ECE Application Programming: Lecture 3
Variables - declaring
var name
memory loc
main() { float hours, payrate; float grosspay; int j;
hours ?
4278
payrate ?
427C
4280
grosspay ? j ?
4284
All variable declarations should be grouped together at the start of the function
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ECE Application Programming: Lecture 3

19. ECE Application Programming: Lecture 3
Variables - assigning
varname = expression;
Declared variable
single variable on left side of =
expression
any legal expression
Expression can be constant, variable, function call, arithmetic operation, etc.
Variable type (int, float, etc) and expression result type should match
If not, funny things can happen ...
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ECE Application Programming: Lecture 3

20. ECE Application Programming: Lecture 3
Variables (cont.)
var name
memory loc
main() { float hours, payrate; float grosspay; int j;
hours = 40.0;
hours
40.0
4278
payrate ?
427C
4280
grosspay ? j ?
4284
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ECE Application Programming: Lecture 3

21. ECE Application Programming: Lecture 3
Variables (cont.)
var name
memory loc
main() { float hours, payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
hours
40.0
4278
payrate
20.0
427C
4280
grosspay ? j ?
4284
6/2/2019
ECE Application Programming: Lecture 3

22. ECE Application Programming: Lecture 3
Variables (cont.)
var name
memory loc
main() { float hours, payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
grosspay = hours * payrate;
hours
40.0
4278
payrate
20.0
427C
4280
grosspay
800.00 j ?
4284
note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive).
6/2/2019
ECE Application Programming: Lecture 3

23. ECE Application Programming: Lecture 3
Variables (cont.)
var name
memory loc
main() { float hours, payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
grosspay = hours * payrate;
j = 5;
hours
40.0
4278
payrate
20.0
427C
4280
grosspay
800.00 j 5
4284
note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive).
6/2/2019
ECE Application Programming: Lecture 3

24. ECE 160 - Introduction to Computer Engineering I
02/09/2005
Variables (cont.)
var name
memory loc
main() { float hours, payrate; float grosspay; int j;
hours = 40.0;
payrate = 20.00;
grosspay = hours * payrate
j = 5;
j = j + 1;
hours
40.0
4278
payrate
20.0
427C
4280
grosspay
800.00 j
5 6
4284
note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive).
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ECE Application Programming: Lecture 3
(c) 2005, P. H. Viall

25. ECE Application Programming: Lecture 3
Example: Variables
What values do w, x, y, and z have at the end of this program?
int main() {
int w = 5;
float x;
double y;
char z = ‘a’;
x = 8.579;
y = -0.2;
w = x;
y = y + 3;
z = w – 5;
return 0; }
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ECE Application Programming: Lecture 3

26. ECE Application Programming: Lecture 3
Example solution
int main() {
int w = 5;
float x;
double y;
char z = ‘a’;
x = 8.579;
y = -0.2;
w = x;
y = y + 3;
z = w – 5;
return 0; }
w = 5
z = ‘a’ (ASCII value 97)
x = 8.579
y = -0.2
w = 8 (value is truncated)
y = (-0.2) + 3 = 2.8
z = 8 – 5 = 3
(ASCII value 3 = "end of text" character)
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ECE Application Programming: Lecture 3

27. ECE Application Programming: Lecture 3
Final notes
Next time
Operators
Output using printf()
Reminders:
Chapter 1 exercises due Monday, 9/10
Chapter 2 exercises due 9/13 & 9/15
Textbook exercises always due 3 days after related lecture—check ”Assignments” tab regularly!!!
Program 1 due Wednesday, 9/12
10 points: register for access to the course textbook
10 points: introduce yourself to your instructor
30 points: complete simple C program
Programs will also require “submission” on Blackboard
To be added by end of today
6/2/2019
ECE Application Programming: Lecture 3