SDT Topic - 08

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SDT Topic - 08

  1. 1. Topic 8 : Array Software Development Techniques
  2. 2. Finding the Highest Number of 3 inputs
  3. 3. Finding the Highest Number of 6 inputs
  4. 4. Introduction • Until now we have been working with single units of data. • A whole number contains a single number, no more. • Today we are going to introduce a new kind of data structure. • The Array • This is a list of similarly types variables. • A list of whole numbers • A list of characters • A list of string
  5. 5. The Problem So Far • Scalability • We can write a program to discover the largest number in a set of five numbers. • But that becomes a much more time-consuming prospect if we want to find the largest in a set of thousand numbers. • The array is used to manage this problem.
  6. 6. The Array • We decide on the size of an array. • We decide on the type of things it will store. • In our pseudocode, we can create an array using the following syntax: • data myArray as array of (10) whole numbers  This creates an array of whole numbers, and provides ten compartments starting the compartment number from 0.  So, compartment number of first compartment is 0.  Compartment number five is the sixth compartment in an array.
  7. 7. The Array • We can put something into a compartment like so: • myArray[5] = 100 • This puts the value 100 into the compartment marked as 5 • It is the sixth compartment. • myArray[7] = 10 • myArray[2] = 40 • We can get information out too: • output myArray[5]
  8. 8. The Array • The number that indicates a compartment is known technically as an index. • The compartment is known as the element.
  9. 9. The Structure of an Array Index Value 0 10 1 50 2 203 3 56 4 79  This is an array of size five.  The contents of myArray[2] would be 203  The square brackets indicate the index
  10. 10. Question • Draw a diagram of an array called myNums which has been initialized to hold 5 whole numbers. Your diagram should indicate the structure of the array, with the different parts clearly labelled.
  11. 11. Finding the Highest Number of 3 inputs
  12. 12. Finding the Highest Number of 3 inputs
  13. 13. Passing an Array to a Function • When we pass an array to a function, we do not specify its size. • There is a size of function that gives you the size of the array. • But not how many elements have been filled.
  14. 14. Passing an Array to a Function • Pseudocode to pass data as array of whole number in function and display it.
  15. 15. Main Program
  16. 16. Desk-Checking Main Function Line Num numbers Remarks 1 0, 0, 0 2 20, 0, 0 3 20, 30, 0 4 20, 30, 15 5 20, 30, 15 Call display(numbers)
  17. 17. Desk-Checking an Array Line Num nums i len Output Remarks 1 20, 30, 15 0 2 20, 30, 15 0 0 3 20, 30, 15 0 3 4 20, 30, 15 0 3 Loop while i is less than len(3) 5 20, 30, 15 0 3 20 6 20, 30, 15 1 3 7 20, 30, 15 1 3 Goto line 4 4
  18. 18. Returning an Array • You can return arrays from your functions just like they were our usual variables. • There are some complications though • If you return an array, it will overwrite in every the array you are using to hold it. • It will overwrite the size. • It will overwrite existing contents. • You can also declare an array without giving a size. • But that sets it as null in your desk-check.
  19. 19. Returning an Array
  20. 20. Main Program
  21. 21. Desk-Checking Main Function Line Num b i sizeof(b) output Remarks 1 null 2 null 0 3 20, 40, 57 0 0 Returning from function 4 20, 40, 57 0 3 Loop while i is less than sizeof b (3). 5 20, 40, 57 0 3 20 6 20, 40, 57 1 3 7 20, 40, 57 1 3 Goto 4 4
  22. 22. Desk-Checking Function Line Num a Remarks 1 0, 0, 0 2 20, 0, 0 3 20, 40, 0 4 20, 40, 57 5 20, 40, 57 return a
  23. 23. Voting Scenario Write pseudo code and source code for following scenario. • The number of different parties standing in the election. This must be a whole number between 2 and 10 inclusive. • Take the name of parties. • The number of votes cast for each party standing in the election. These must be whole numbers between 0 and 600,000 inclusive.
  24. 24. Two Dimensional Arrays • The concepts are identical. • You just need two indexes, and two sets of sizes. • These are grids of data. • Two dimensional arrays allow for several kinds of programs that would otherwise be very difficult. • Especially games
  25. 25. Two Dimensional Arrays • Creating • data myGrid as array (10, 10) of whole numbers • Or • Data myGrid as array (10)(10) of whole numbers • Setting • myGrid[10, 5] = 100 • Or • myGrid[10][5] = 100
  26. 26. Two Dimensional Arrays • Getting • Output myGrid [10, 5] • Or • Output myGrid[10][5]
  27. 27. Two Dimensional Arrays Example 1. data i as whole number 2. data j as whole number 3. data str as array(2)(2) of String 4. str[0][0] = "Nepal" 5. str[0][1] = "America" 6. str[1][0] = "Australia" 7. str[1][1] = "England"
  28. 28. Two Dimensional Arrays Example 8. i = 0 9. loop while i is less than sizeof(str) 10. j = 0 11. loop while j is less than sizeof(str[i]) 12. Output str[i][j] 13. j = j + 1 14. end loop 15. i = i + 1 16.end loop
  29. 29. End of Topic 8 Software Development Techniques

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