Hello World 2 What does all that mean?. The Evolution of Programming Languages Early computers programmed in machine language To calculate wages = rate.

Hello World 2What does all that mean?

The Evolution of Programming Languages

• Early computers programmed in machine language

• To calculate wages = rate * hours in machine language:

100100 010001 //Load

100110 010010 //Multiply

100010 010011 //Store

The Evolution of Programming Languages (cont’d.)

• Assembly language instructions are mnemonic • Assembler: translates a program written in

assembly language into machine language

The Evolution of Programming Languages (cont’d.)

• High-level languages – Express algorithms at a more abstract level:int wages = rate * hours;

– Ex: Basic, FORTRAN, COBOL, Pascal, C, C++, C#, and Java• http://oreilly.com/news/graphics/prog_lang_poster.pdf• http://www.digibarn.com/collections/posters/tongues/tongues.jpg

• Current popularitieshttp://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

The Evolution of Programming Languages (cont’d.)

• Compiler: translates a program written in a high-level language into machine language

Processing a C++ Program (cont’d.)

• To execute a C++ program:– Create a text source program in C++– Preprocessor directives begin with # and are

processed by the preprocessor– Compiler:• Checks that the program obeys the language rules• Translates into machine language (object program)

Processing a C++ Program (cont’d.)

• To execute a C++ program (cont'd.):– Linker: • Combines object program with other programs

provided by the SDK to create executable code• Library: contains prewritten code you can use

How the code works:

• # : preprocessor directive– Instructions to do before compiling– Bring the code from the library iostream into this

file

How the code works:

• Use all the names that are in the "standard" grouping in my program

• Alternative:

How the code works:

• ; statement terminator– Ends a "sentence of code"

How the code works:

• int main()– The starting point of our program– Program instructions go inside { }

How the code works:

• Comment : computer ignores– // : rest of line is comment– /* : everything is comment until */– /** : special comment – machine readable

Documentation

• Every file should have comment like this at top:

How the code works:

• cout : console output

How the code works:

• cout : console output<< "send to output"

How the code works:

• cout : console output<< "send to output""Hello" : a string – piece of text

How the code works:

• cout : console output<< "send to output""Hello" : a string – piece of textendl : symbol representing "end of line"

How the code works:

• return 0– Program ran successfully– Anything BUT 0 indicates error

Working with numbers

• We can output numbers to console:

• Can do math using + - / *– Division may give interesting results…

Everything Counts

• Indentation & Style matter (to humans)• Spelling & Capitalization matter (to humans &

computers)