KH       Computational Physics- 2012                   Programming
      Short test of C++ knowledge
       • Whatisaclass?
       • Whatisvirtual function?
       • Whatistemplate?
       • Whatisimplicit type conversion?
       • Whatmeansexplicit?
         class A{
            int a;
          public:
            explicit A(int a);
         };
       • Whatisreturn value optimization?
       • Whatisthedifference between ”new” ”new[]” and ”operator new”?
       • Whatisplacement new?
           class A;
           void memory = operator new(size);
              *
           a = new(memory) A;
       • Whatismap?
       • Whatisdeque?
                                 Kristjan Haule, 2012                   –1–
      KH         Computational Physics- 2012                         Programming
                              Programminginhigh-level
                                      languages
       There is no ”perfect” computer language. The best choice depends on the problem.
       For numerics, if speed is of upmost importance:
        • fastest: Fortran77 (no aliasing)
        • similarly fast: Fortran90, C, C++
        • not so fast: Java, any interpreter (Perl, Python)
       (aliasing: concurrent acces to a single entity causes synchonization problems and resuls in performace loss).
       Humantimenecessarytowrite andmantain large scale projects:
        • Python
        • C++, Java
        • C, Fortran 90
        • Fortran77
                                      Kristjan Haule, 2012                        –2–
     KH       Computational Physics- 2012               Programming
     For some purposes like manipulating files, writting small scripts or working with strings of
     text (parsing) the best choice are interpreters: Phython, Perl...
     Historical overview on computer language development can be found at
     http://en.wikipedia.org/wiki/Timeline_of_programming_languages
     There are thousands of programming languages and new ones are created every year.
                                Compilers: Fortran, C, C++, Pascal, (Java), ...
                              Interpreters: Perl, Phython, Mathematica, (Java), ...
     Compilers: Code needsto be compiled and translated from the original language into
     machine-code(assembler). Machine code in form of an executable can be run. When you
     run the program, the computer executes the machine-code instructions in sequence.
      • advantage: The machine-codecan be very optimized and execution is fast.
      • dissadvantage:
         – Theoriginal program is no longer connected to the machine-code, and mapping the
          machine-codebackto the original program can be very difficult (hard job for
                               Kristjan Haule, 2012                –3–
      KH        Computational Physics- 2012                        Programming
            debugger, hard to connect run-time errors with the bugs in the original code)
          – Eachprocessortype has a different machine code and thus requires a completely
            different compiler.
          – Thecodecan-notbechangedonfly,muchlessflexibleandusuallyharderto code.
      Interpreters: Converts each line of a program into machine language as the statement is
      encountered. If a statement is encountered multiple times (as occurs in a loop) the machine
      mustconvert it to machine language each time.
        • advantage:
          – Easyto detect bugs because original program is still closely related to execution.
          – Noseparateexecutablefile need be stored and the same code usually runs on
            manyplatforms
          – Usually offer more flexibility and provide more powerful statements (regular
            expressions in Perl or Phython, Simplify,Solve,... in Mathematica,...)
          – Codeoftheoriginal program can be changed on the fly (can be very powerful)
        • dissadvantage: speed - Translating the same line of code into machine-code and then
          executing the machine-code has quite a high overhead.
                                     Kristjan Haule, 2012                       –4–