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  1. Programming Languages and Software Engineering

  2. Topics • discuss some of the underlying commonalities and differences among programming languages • explain what there is to learn about software engineering beyond programming

  3. Learn Programming in Ten Years(Peter Norvig) • it takes time/practice/experience to learn to become a good programmer • you can learn syntax in one semester (or from a book), but... • need to built up a repertoire of problems you have previously solved, so when you face a new problem, you can draw upon your prior experience, you’ve seen it before – “design patterns”

  4. Norvig’s suggestions: • Get interested in programming, and do some because it is fun.. • Program. The best kind of learning is learning by doing. • Talk with other programmers; read other programs. • Work on projects with other programmers. • Work on projects after other programmers. • Learn at least a half dozen programming languages. • Remember that there is a "computer" in "computer science". Understand how it works. • Get involved in a language standardization effort.

  5. In CSCE 121, we teach C++ because it is widely used for large industrial applications. • Many additional computational concepts are introduced in this course, such as how compilers work, object-oriented design, etc. • There are many other languages - do you need to learn them all?

  6. Assembler • Fortran, Pascal, COBOL, Basic • Ada, Modula, PL/1, Simula, MatLAB • Haskell, LISP, Scheme • C, C++, C#, Objective-C • Smalltalk, Java, Javascript • PERL, PHP, TCL, Python, Ruby • csh, awk, sed • Prolog – a logic-based language for making inferences from knowledge bases • Postscript – a stack-based language for printers

  7. source:

  8. Two Interesting Questions • Why are there such a bewildering array of languages? • historical artifact – some languages evolved into, or inspired, other languages • some languages started out as experiments to test new ideas or features, like OO and message-passing in Smalltalk • some languages are more suited for certain applications, like Fortran for numerical computing, or PERL/Python for processing text files • there are special-purpose languages like Postscript (or MatLAB, Simula) that are custom-designed for certain tasks (printing, simulations...)

  9. Two Interesting Questions • Isn’t C++ overkill for writing low-level code like drivers/controllers/firmware? wouldn’t C be much more efficient with less overhead? • this is a common misconception • by this reasoning, why not use assembler? • modern C++ compilers have many optimizations that make code fast/competitive • most importantly, C++ allows code to be expressed in a more comprehensible (generic, factored) way that facilitates maintainability and long-term use of code over many years • these issues often outweigh a few extra microseconds • the original programmer might be long gone, and someone else has to find and fix a bug

  10. Programming • The same algorithm can be implemented in many programming languages. in C in Python in Java #include <stdio.h> void main(int argc,char*argv) { int a,b,temp; sscanf(argv[1],”%d”,&a); sscanf(argv[2],”%d”,&b); if (a<b) { temp=a; a=b; b=temp; } while (b>0) { int r=a%b; a=b; b=r; } printf(“GCD is %d\n”,a); } import sys if __name__==“__main__”: a = int(sys.argv[1]) b = int(sys.argv[2]) if a<b: b,a = a,b while b>0: r = a%b a,b = b,r print “GCD is”,a public class GCD { public static void main(String[] args) { int a,b,temp; a=Integer.parseInt(args[0]); b=Integer.parseInt(args[1]); if (a<b) { temp=a; a=b; b=temp; } while (b>0) { int r=a%b; a=b; b=r; } System.out.println( "GCD is "+a); } } • Point #1: Once you understand the general principles (which you will learn in CSCE 314), you just have to learn the “syntactic variations” in each language • Point #2: There are some unique language differences/features including: user-created types, polymorphism, list comprehension, exceptions, function objects...

  11. In CSCE 314, you will learn the structure of languages and what unites them, so you can eventually learn to program in any of them • major classes of languages • imperative/procedural languages (“block-structured”) • Pascal, Fortran, C, Ada... • functional languages (“expression evaluation”) • Scheme, LISP, Haskell... • object-oriented (encapsulation, “message passing”) • Smalltalk, Java, Objective-C, C++ • logic-programming • Prolog • (of course, some languages blur these distinctions)

  12. I already showed examples of procedural programming • here is the functional version of factorial and GCD written in LISP: • (this is an interactive command line I typed into) >(defun fact (n) (if (<= n 1) 1 (* n (fact (- n 1))))) FACT >(fact 10) 3628800 >(defun gcd (x y) (if (< x y) (gcd y x) (if (= y 0) x (gcd y (mod x y))))) GCD >(gcd 112 40) // “running a program” is done by “evaluating an expression” 8

  13. interpreted vs. compiled languages • interpreters – read in lines and execute directly • compilers • convert source code to low-level language (.exe, assembly language, executable CPU instructions) • have to learn about regular expressions, parsing, syntax and semantics, optimization... • compare Python and C • block structure • think how the “body” of a for loop or if statement is marked in different languages (“}”, “endfor”, change of indentation) • type systems • can users define new “types” and operations on them? like structs and classes, example: Complex #s • object-oriented languages • classes, inheritance, polymorphism... • extensions for: concurrency, exception-handling, real-time applications...

  14. public class Rectangle { int height,width; // interval variables // initializer public Rectangle(int a,int b) { height=a; width=b; } int area() { return height*width; } } static Rectangle BoundingBox( Rectangle A,Rectangle B) { int h=max(A.height,B.height); int w=max(A.width,B.width); Rectangle C=new Rectangle(h,w); return C; } public static void main(String[] args) { Rectangle P=new Rectangle(3,2); Rectangle Q=new Rectangle(1,4); Rectangle R=BoundingBox(p,q); System.out.println( “P:(3,2) area="+P.area()); System.out.println( “Q:(1x4) area="+Q.area()); System.out.println( “R:(3x4) area="+R.area()); } • Here is an example of an object-oriented definition of Rectangles in Java 27 sun> java local/testRectangle p:(3,2) area=6 q:(1x4) area=4 r:(3x4) area=12 P: h=3, w=2 R: h=3, w=4 Q: h=1, w=4

  15. Learning Unix (part of CSCE 312/Systems) • why learn this? is it necessary? • many command-line development tools • (compared to IDEs like MS Visual Studio) • Unix has well-defined concepts and principles • executables, flags, pipes, streams, sockets... • multitasking • many powerful tools for software development: • editors like Emacs • compilers like g++ • make files (for multi-file projects) • debuggers like gdb • source-code control like CVS or SVN

  16. Software Engineering (CSCE 431) • software engineering usually involves working in teams • requirements gathering/writing specifications (with customer) • UML (Unified Modeling Language) • diagram out how your modules work and interact • libraries – reuse of code • e.g. APIs for image processing, network access, speech recog... • large projects have many dependencies • testing – defining test cases as important as writing code • documentation • explain how things work, why it was designed that way, ASSUMPTIONS, alternatives, limitations... • version control • issue new number with each change to file, e.g. v3.0.12 • critical so you can identify and undo mistakes • life-cycle models • waterfall, rapid prototyping, extreme programming (partners)... • metrics for tracking/estimating number of bugs over time