Programming Languages

• Binary
  • We use decimal, or base 10
    • Each digit in the system represents a power of 10.
    • 486.23 = 4 * 100 + 8 * 10 + 6 + 2/10 + 3/100
    • 486.23 = 4 * 10 ² + 8 * 10¹+6*10⁰ + 2 * 10^-1 + 3 * 10 ^-2
    • This requires 10 digits (0,1,2,3,4,5,6,7,8,9)
  • This is diffacult to represent electronicaly
  • So in computers, we use base 2, or binary
    • Each digit represents a power of 2
    • The only digits are 1 or 0
    • 11010 = 1 * 16 + 1 * 8 + 0 * 4 + 1 * 2 + 0
    • 11010 = 1 * 2⁴  + 1 * 2³ + 0 * 2² + 1 * 2¹ + 0 * 2⁰
  • We encode, or represent in binary, all data used in the computer.
    • Characters are encoded using ascii (a = 01010001).
    • Integers are their binary representation.
    • Floating point (real numbers) are much more complicated.
  • We won't have to worry about this too much at this point.
  • But that is why we always encounter powers of two (1024)

• Levels of programming languages
  • Machine Language
  • Assembly Language
  • High Level Language
  • Interpreters
  • Compilers
  • Source Code
  • Machine Code
  • Executable
  • Portable
• Just like a with human language, each programmer develops their own style.
  • Based on the rules
  • And the norms (what people tell us we must do, but can't enforce)
  • What we see others do.
• What can a computer do?
  • Move data around
  • Receive input, and produce output
  • Compare two values and see if they are equal or not
  • Perform arithmatic.
• A programming language supports these features.
• Just like following a recipie, we must do some things in order.
  • This is the flow of control or sequence.
  • Sometimes we break a recipie down
    • To make a pie, make a crust and make the filling
    • We do this with programs as well, they are called subprograms
  • Sometimes we repeat things
    • kneed the dough for 5 minuets
    • We do this with programs as well, we call it a loop
  • Decisions
    • If the dough is too stickey, add more flower
    • This is called selection.
  • These in general are called control structures.
• Consider balencing your checkbook:
  • We have a starting balence
  • We have a series of deposit slips and checks
  • What do we do?