Review: computer memory

  • Recall that the computer memory consists of a series of electical switches and each switch can store/remember one of the value of 0 or 1:

            

  • We have also learned that:

      • The computer memory contains the computer program !     

  • Therefore:   a computer program is a bunch of binary numbers !!

How people program a computer around 1945

  • Programmers would set switches to on/off to write out the computer instruction in binary:

  • Programming was a very tedious task !

How people program a computer around 1950

  • We invented the assembler programming language which are mnemonics for each binary machine instruction:

  • A (simple) translation program can an assembler translates an assembler program to binary machine code

How people program a computer around 1957

  • The first programming language (Fortran) was invented:

  • A complex translation program can an compiler translates a Fortran program to assembler code

Demo the C compiler

  • I don't have a Fortran compiler

  • I do have a C compiler

  • Here's a small C program: 

      int a, b, c;

int main()
{
   c = a + b;             
}

  • I will show you the output (= assembler program) generated by the C compiler

    (Note to self: do it on a Windows machine)

Another way to run computer programs   (How Python execute a program)

  • There is another way to execute computer programs:

  • An interpreter is a computer program that understands and execute a certain programming language (e.g.: Python)

  • The interpreter reads in one statement from a program at a time and execute it

    Executing a statement will update variables inside the interpreter