Computers, Program Execution, and Data Representation

Tom Kelliher, CS 102

Jan. 25, 1999

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First quiz on Friday.

Introductory exercises.

Assignment

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Outline

  1. Program execution.

  2. A model computer.

  3. Data representation.

Coming Up

MS Word --- bring the workbook.

Program Execution

Consider the following simple program:

 1:   let sum = 0
 2:   print "How many numbers? "
 3:   read count
 4:   let loopCount = count
 5:   if loopCount equals 0 goto 11
 6:   print "Next number: "
 7:   read input
 8:   let sum = sum + input
 9:   let loopCount = loopCount - 1
10:   goto 5
11:   let average = sum / count
12:   print "The average is:", average, "."
13:   end
  1. Where do we begin?

  2. After completing one step, where do we proceed?

  3. Operations: assignment, arithmetic, decision, branch, I/O.

  4. Operands: Variables, constants (numeric and string).

The Basic Parts of a Computer

A block diagram:

  1. What is memory? How does it differ from storage?

  2. What parts of a PC are considered input devices? Output devices? Both?

Data Representation

  1. Computers use the binary system. Why?

  2. Binary digits.

  3. Bits, bytes, words.

  4. Memory locations: cells with addresses.

  5. Converting between binary and decimal:
    1. Binary to decimal: Consider some examples. 1, 10, 100, 110. What to do in general?

    2. Decimal to binary: We need a little algorithm.
      read decimalNumber
      while decimalNumber does not equal 0
      {
         let remainder be the remainder of decimalNumber / 2
         let decimalNumber be the integer quotient of decimalNumber / 2
         print remainder to the left of any other digits printed
      }
      

  6. How do we represent characters? ASCII code:
    1. A: 01000001

    2. 4: 00110100

  7. How does the computer know if a memory location contains numbers, characters, variables, or instructions?



Thomas P. Kelliher
Sun Jan 24 18:45:59 EST 1999
Tom Kelliher