Hello World 2 What does all that mean?
Feb 24, 2016
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)