Introduction To Programming

• Programming and the uses of the word
  • A computer runs a program, which is a series of instructions written in the language a computer can follow.
  • The language is machine language.
    • Machine language is unique to each processor family
    • It is usually expressed in binary.
    • Look at vim (od /usr/bin/vim)
    • This is the only language a computer "understands".
  • An assembly language is
    • A language that is very close to binary
    • It is in a human readable form
    • But it is very difficult to read.
    • It is translated by an assembler from assembly to machine language.

    • # introductory example; finds the sum of the elements of an array
       
      .data  # start of data segment
      
      x:    
            .long   1
            .long   5
            .long   2
            .long   18
      
      sum:
            .long 0
      
      .text  # start of code segment
      
      .globl _start
      _start:
            movl $4, %eax  # EAX will serve as a counter for 
                           # the number of words left to be summed 
            movl $0, %ebx  # EBX will store the sum
            movl $x, %ecx  # ECX will point to the current 
                           # element to be summed
      top:  addl (%ecx), %ebx
            addl $4, %ecx  # move pointer to next element
            decl %eax  # decrement counter
            jnz top  # if counter not 0, then loop again
      done: movl %ebx, sum  # done, store result in "sum"
      	     

  • A High Level Language is a language for expressing a computer program which is related to human languages.
    • There are many high level languages (see the Wikipedia List)
    • And no clear picture of which is "Best"
    • Compiled languages use a compiler to translate the entire program to machine language.
    • (A compiler is a program which translate from a high level language to machine language. A compiler does this to an entire program in one pass.
    • Think translate "Hamlet" to Klingon,
    • Interpreted languages use an interpreter to interpret, then execute one line of a program.
    • An interpreter is a program which translates and executes a program one line at a time.
    • Run Python
    • Think interpreting a speech from the Klingon Representative at the UN as it is given.
  • C++ at EUP
    • We have selected C++ as our primary language at Edinboro.
    • It is a superset of C (If you know C++ you know C).
    • It is a reasonably popular language.
    • It is a reasonably modern language.
    • It is the workhorse of Computer Science.
    • It is an open, standards based, and universally available language
    • We learn it in quite a bit of detail.
      • 130, 230, 330
  • The word program
    • A source program (or source code) is a program written in something other than machine language. It needs to be translated into machine language before it can be run (or executed)
    • An object program, or program, is a machine language program which is ready to be run (or executed)
    • An object program is frequently referred to as an executable
    • A program which is running is called a process.
    • But all are informally referred to as a program.
• Programming
  • Is the act of creating a computer program. (executable)
  • This can be done in a text (command line) or graphical (GUI) environment.
  • It involves several tools and processes.
    • Connection to the machine on which the program is to be written.
    • The operating system. (Windows, linux, ...)
    • A shell, or command line environment. (possibly)
    • A text editor
    • A compiler