1. ECE 103 Engineering Programming Chapter 5 Programming Languages
Herbert G. Mayer, PSU CS
Status 6/10/2016
Initial content copied verbatim from
ECE 103 material developed by
Professor Phillip PSU ECE

2. Syllabus What’s This Blue Code? Introduction
Computer Architecture Overview
Machine Language
Assembly Language
High-Level Language
C Programming Language

3. What’s This? // Assume non-negative args. Should be “unsigned”
int fact( int arg )
{ // fact
if ( arg <= 1 ) { // fact(0) = fact(1) = 1
return 1;
}else{
return fact( arg – 1 ) * arg;
} //end if
} //end fact
int main( /* no params */ )
{ // main
printf( “Factorial %d = %d\n”, 10, fact( 10 ) );
return 0;
} //end main

4. Introduction What is a program?
Software that runs on an standard computer
Word processor, database engine, web browser, video game, graphics package, simulator, etc.
Where else are programs found?
Embedded – Microwave oven, engine controller, media player, thermostat, pacemaker, toy, etc.
Electromechanical – Early computers (e.g. ENIAC)
Mechanical – Jacquard loom (1801), Babbage analytical engine (1837)
Biological – Instinctive and learned behaviors 3

5. What do programs do? Perform “useful” computation or IO
Process information
Input  Program  Output
Programs may require input (but not always)
numeric or text input, sensor values, etc.
Programs may generate output (but not always)
text, graphics, actions such as triggering devices 4

6. Traditional approaches:
How are programs created?
Develop an algorithm for the solution in your head
Write a program via a computer file; textual
Programming languages provide syntax for implementing algorithms on a computer
Traditional approaches:
Machine language
Assembly language
High-level languages, generally machine-independent 5

7. Classic Computer Architecture Overview
Simplified computer model:
Main Memory
(RAM, ROM)
Auxiliary Storage
(e.g., disk drives)
Input
(e.g., keyboard, mouse)
Output
(e.g., monitor, printer)
Processor
(CPU) 6

8. The processor executes the program's instructions.
Instruction Decoder
Memory Interface
To main memory
Registers
(fast memory)
ALU
The ALU (Arithmetic Logic Unit) performs basic arithmetic, logic, and comparison operations. 7

9. Each memory location is assigned a unique address.
Program instructions and data are stored in computer memory (e.g., RAM or sometimes ROM)
Each memory location is assigned a unique address.
Address 1 2 3 :
253
254
255
Stored Value v0 v1 v2 v3 :
v253
v254
v255 8

10. Example: Vintage CPU (1975)
MOS 6502
Single core
8-bit data
Memory
64 KB main
Registers:
Accumulator (A)
Index (X, Y)
Processor Status (P)
Stack Pointer (S)
Program Counter (PC)
Speed: 1 to 2 MHz
Process: 8 m
# of transistors: ~3500
Pin-out
Die Shot 9

11. Example: Modern CPU (2013) Intel i7-4770 Haswell Four cores
64-bit data
Memory
4x256 KB L2 cache
8 MB L3 cache
32 GB main (3.2x107 KB)
Registers:
bit
16 64-bit
Integrated GPU
Speed: 3.4 GHz (3400 MHz)
Process: 22 nm (0.022 m)
# of transistors: ~1.4 billion
Package
Die Shot 10

12. Machine Language
Machine language (ML) is a set of very low-level instructions that directs a computer processor to perform specific elementary operations
Not to be confused with the programming language ML!
Each CPU family has its own, unique ML
Deep expertise needed to write ML programs 11

13. Stored Instruction or Data
How does a computer run ML programs?
A machine language program consists of processor instructions and data that are stored in memory
Example:
6502 CPU
(start address = $600)
e.g., A9 represents the
CPU’s “Load Accumulator”
instruction
Stored Instruction or Data
binary
hex A9 5A 18 69 20 8D 00 10
Address (hex)
600
601
602
603
604
605
606
607 12

14. The CPU’s program counter contains the address of the next instruction to execute
Processor cycle:
Retrieve an instruction from memory
Decode the instruction
Act on the instruction
Increment the program counter
Example:
Visual CPU Simulator – 13

15. Assembly Language
ML coding is tedious and error-prone, so more advanced languages were developed
Assembly language programs (AL) use mnemonics (symbolic names and keywords) instead of binary digits
AL programs are easier to write, understand, and modify than ML programs; but still tedious 14

16. Example: AL version of previous ML code
600: A9 5A LDA #$5A ; Load accumulator with number
602: 18 CLC ; Clear carry flag
603: ADC #$20 ; Add $20 to accumulator w/carry
605: 8D STA $1000 ; Store accumulator at $1000
An assembler translates an assembly program to machine language
Assembly language still requires a high level of programmer expertise
Example:
Easy 6502 – 15

17. High-Level Languages
A high-level language (HLL) uses a more natural language approach to keywords and syntax
A single HLL statement may be equivalent to many machine or assembly instructions
Abstract algorithms are easier to implement in HLL
It is easier to write, maintain, modify, and port programs using a high-level language; result: Higher productivity 16

18. Example: HLL version of previous ML code
m = 0x5A + 0x20; /* Add hex $5A and $20 */
A compiler or interpreter translates a high-level program to machine code
Many HLLs (several hundred) exist:
FORTRAN, COBOL, Lisp, BASIC, …
Pascal, C, C++, C#, Java, Python, …
An HLL increases programmer productivity (again)! 17

19. The C Programming Language
C was developed by Dennis Ritchie in the early 1970s for use on UNIX systems at Bell Labs
C is “high-level” because it supports structured programming practices
C also is “low-level”, as it permits access to underlying computer hardware
C is an international standard (ISO)
C widely used in engineering, scientific, and business disciplines:
Efficient, good performance, portable 18

20. C Language Evolution 1969 to 1973 – C (Bell Labs initial development)
1978 – K&R C (Kernighan and Ritchie)
1989 – C89 (ANSI)
1990 – C90 (ISO)
1995 – C90 Normative Amendment 1 → "C95"
1999 – C99 (ISO)
2011 – C11 (ISO)
ANSI C89 and ISO C90 are the same standard. 19