Hand Crafting your own program

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Hand Crafting your own program

• By Eric Davis
• for CS103

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How to make your own programs

• General format of a program.
• How to read a problem.
• What variables do I want?
• Take in user input
• Crunch and compute
• Spit the answer out.

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General Format of a Program
ltAny Required Headersgt ltVariable
Declarationsgt ltGet User Inputgt ltMake
Computations on Inputgt ltOutput Resultsgt ltAny
Required Closing stuffgt
Can be repeated
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How to read a problem.

• When reading a problem, try to extract the
  information you need and disregard the other
  stuff.
• Identifying the important elements of the problem
  is the most important step in creating a correct
  computer program

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An example problem

• Write a program that reads in three numbers and
  output the product of the numbers.
• Identify the important words.
• --------------------------------------------------
  -----

Write a program that reads in three numbers and
output the product of the numbers.
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Reading the problem

• What it says
• Three Numbers
• Product

• What it might mean
• Need to have three number variables
• Output the multiplication of the three numbers.

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What variables do I want?

• Every program needs some variables.
• Fit the variables to the problem. If you need to
  store numbers, you will need ints or doubles,
  probably. If you need to store words or letters,
  you will need Strings or chars.

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Our example continued

• We need to take in three numbers, so well
  probably need three number variables.
• The problem didnt say if they were integers or
  real, so we want to probably go with most
  general- double.

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Our example continued

• The problem also mentioned that we need to output
  the product, which is again a number variable.
• Since our product will be calculated from the
  three doubles, we will probably want this also to
  be a double.

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Starting our program
Required Header Stuff
public class Product public static void
main(String arg) double user10, user20,
user30 double productOfUsers0
Variable Declarations
Good idea to initialize.
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Taking in user input

• Comprised of two parts
• Prompting the user for input.
• Taking in the input
• Often this process is repeated multiple times, to
  take in multiple pieces of data. It will be in
  our example so that we can take in three numbers.
  

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Our program taking form...
public class Product ... System.out.println(
Enter first number) user1
SavitchIn.readLineDouble() System.out.println(E
nter second number) user2
SavitchIn.readLineDouble() System.out.println(E
nter last number) user3 SavitchIn.readLineDo
uble() ...
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Crunch, compute, calculate

• Once we have the information that we need, we can
  start making calculations.
• In our example, we now have all the data to make
  the product.

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The return of the program...
public class Product ... productOfUsers
user1user2user3 ...
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Show the answer

• Now that the computer has made the calculations
  it needs to, we need to have it give the answer
  to us humans in some meaningful format.
• Usually need to concatenate (glue) some text
  strings and some variables together.

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The end of the program
Public class Product ... System.out.println(
The Product is productOfUsers) ...

Concatenate
Can be on separate lines, just dont break up
lines in the middle of a string.
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There can be more than one...

• The solution we created is not the only way of
  solving the problem. It can be done with
  different algorithms, with fewer variables, etc.
  This is just a good general outline of how to
  make your own program.

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More examples to try

• Create a program that asks a user for a number of
  characters(up to 8) and then takes in that number
  of characters from the user(1 per line). The
  program then outputs the characters in reverse
  order.

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More Examples to try

• Read in a 4-digit number and output each digit on
  a separate line (Hint, modulo and division). An
  example would be
• Enter a number 1324
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