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  1. Useful resources • Safari Tech Books Online • Free access to 250 books from library • Full access starts from $9.99/month • MSDN • Comprehensive MS products references • www.cplusplus.com • No-frills C++ references • Key is to know how to ask the correct question Chapters 9 & 10 Arrays & Strings

  2. Chapters 9 & 10 Arrays

  3. Simple vs. Structured Data Type • Simple data type • Can store only one value at a time • Structured data type • Each data item is a collection of other data items • Why need structured data type • If a program needs to operate on test scores of 50 students, should it declare 50 variables? How? Chapters 9 & 10 Arrays & Strings

  4. Arrays • Definition • A collection of a fixed number of components of the same data type • Declaration dataType arrayName[intExp]; e.g. int n[5]; • One dimensional Elements are arranged in a list form 4 Bytes Array size MUST be known when compiling n[1] n[2] n[3] n[4] n[0] Chapters 9 & 10 Arrays & Strings

  5. Arrays • Accessing array components (elements) arrayName[intExp] • Initialization duringdeclaration int a[3] = {2, 5, 8};int b[] = {2, 5, 8};int c[3] = {2}; //partial initint d[3] = {2, 5}; //partial init Index, Subscript • Non-negative int • Starts at 0 • Ends at size-1 Chapters 9 & 10 Arrays & Strings

  6. Arrays • Basic processing • Using loop to traverse the array • Initializing • Reading data • Printing • Finding sum and average • Largest/smallest element • No guard against out-of-bounds subscripts • No aggregate operation • What’s in the name of array?Base address of the array Chapters 9 & 10 Arrays & Strings

  7. Passing Arrays to Functions • By reference only • Syntax • Formal parameter must have [] • Actual parameter doesn’t have [] • Constant arrays as formal parameters • Values of const formal parameters are not allowed to change during function execution • Checked at compile-time • Function cannot return an array Chapters 9 & 10 Arrays & Strings

  8. Sequential Search • Algorithm • Starts from the first element • Traverses the entire array until • Finds the search term Or • Reaches the last element • Does not assume the array is sorted Chapters 9 & 10 Arrays & Strings

  9. Selection Sort • Algorithm Sort x[n] in ascending order • Find the smallest element in the entire array and swap it with x[0] • Find the smallest element in the unsorted portion (from x[1] to x[n-1]) of the array and swap it with x[1] • Find the smallest element in the unsorted portion (from x[2] to x[n-1]) of the array and swap it with x[2] • ... • Find the smallest element in the unsorted portion (from x[n-2] to x[n-1]) of the array and swap it with x[n-2] Chapters 9 & 10 Arrays & Strings

  10. Initial state 1st pass finds x[7] to be the smallest After the 1st pass Chapters 9 & 10 Arrays & Strings

  11. After the 2nd pass 5 7 24 30 25 62 45 16 65 50 After the 3rd pass 5 7 16 30 25 62 45 24 65 50 After the 4th pass 5 7 16 24 25 62 45 30 65 50 After the 5th pass 5 7 16 24 25 62 45 30 65 50 After the 6th pass 5 7 16 24 25 30 45 62 65 50 After the 7th pass 5 7 16 24 25 30 45 62 65 50 After the 8th pass 5 7 16 24 25 30 45 50 65 62 After the 9th pass 5 7 16 24 25 30 45 50 62 65 Chapters 9 & 10 Arrays & Strings

  12. Binary Search • Requires the array to be sorted • Algorithm • Search for key in x[n] (in ascending order) • Compare key with the middle element. if key is less than the middle element, search the lower half; otherwise, search the upper half • Repeat the previous step until • Key is found Or • Impossible to divide the array again Chapters 9 & 10 Arrays & Strings

  13. first=mid+1 mid last 5 7 16 24 25 30 45 50 62 65 mid first last=mid-1 5 7 16 24 25 30 45 50 62 65 Search for 30 [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] first mid last 5 7 16 24 25 30 45 50 62 65 Found!!! Chapters 9 & 10 Arrays & Strings

  14. first=mid+1 mid last 5 7 16 24 25 30 45 50 62 65 mid first last =mid-1 5 7 16 24 25 30 45 50 62 65 mid first =mid+1 last 5 7 16 24 25 30 45 50 62 65 =mid-1 last first 5 7 16 24 25 30 45 50 62 65 Search for 35 [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] first mid last 5 7 16 24 25 30 45 50 62 65 Not Found!!! Chapters 9 & 10 Arrays & Strings

  15. Two-Dimensional Arrays • Data are stored in table form Chapters 9 & 10 Arrays & Strings

  16. Two-Dimensional Arrays • Declaration int inStock[6][5]; • Initialization during declaration int inStock[6][5] = {{10, 7, 12, 10, 4}, {18, 11, 15, 17, 10}, ... ..., { 9, 4, 7, 12, 11}}; • Accessing inStock[0][0] inStock[5][4] • Passing to functions • By reference only • Number of columns must be specified when declaring a 2-d array as formal parameter void f(int stock[][5], int rowSize) { } Chapters 9 & 10 Arrays & Strings

  17. char[] vs. string • C-strings • character arrays terminated with the null character ‘\0’ • <cstring> • string data type • Not null-terminated • <string> char cname[5] = “John”; string sname = “John”; J o h n \0 J o h n Chapters 9 & 10 Arrays & Strings

  18. More on string data type • Some useful functions • +, length(), size(), find(), substr(), … • pp. 498 / pp. 1261-1264 • Array of strings using string type • Similar as other one-dimensional arrays of built-in type Chapters 9 & 10 Arrays & Strings

  19. Increase New customer Programming Example • Customer data • Customer ID • First name • Last name • Mileage balance • New transactions • Customer ID • First name • Last name • New mileage 1R67S34 Graham Greene 20000 34TS8R3 Frederick Forsyth 30000 K2L398D Tom Clancy 4000 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000 WMK85S3 Ken Follett 1000 Chapters 9 & 10 Arrays & Strings

  20. Algorithm • Read customer data into arrays • Read one new transaction • Process the new transaction • Repeat steps 2 and 3 until the end of the file • Save the updated customer data Chapters 9 & 10 Arrays & Strings

  21. Algorithm • Read customer data into array • Declare four parallel arrays, initialize # of customers to zero • Read string1 • Read string2 • Read string3 • Read integer • Assign three strings and one integer to the current position , the index of which is equal to the current # of customers, of the four parallel arrays • Increase # of customers by 1 • Repeat steps 2-7 until the end of the file • Read one new transaction • Process the new transaction • Repeat steps 2 and 3 until the end of the file • Save the updated customer data 1R67S34 Graham Greene 20000 34TS8R3 Frederick Forsyth 3000 K2L398D Tom Clancy 4000 Chapters 9 & 10 Arrays & Strings

  22. Algorithm • Read customer data into array • Read one new transaction • Read string1 • Read string2 • Read string3 • Read integer • Process the new transaction • Repeat steps 2 and 3 until the end of the file • Save the updated customer data 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000 WMK85S3 Ken Follett 1000 Chapters 9 & 10 Arrays & Strings

  23. Algorithm • Read customer data into array • Read one new transaction • Process the new transaction • Search for the id in id array • If found, increase the corresponding component of mileage array by the new mileage; otherwise, add a new component to the end of each of the four arrays and increase the # of customers by 1 • Repeat steps 2 and 3 until the end of the file • Save the updated customer data 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000 WMK85S3 Ken Follett 1000 Chapters 9 & 10 Arrays & Strings

  24. 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000WMK85S3 Ken Follett 1000 id fName lName mileage 0 “1R67S34” “Graham“ “Greene“ 20000 1 “34TS8R3” “Frederick” “Forsyth” 30000 2 “K2L398D“ “Tom” “Clancy” 4000 3 4 5 6 ... ... ... ... 99 Chapters 9 & 10 Arrays & Strings

  25. 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000WMK85S3 Ken Follett 1000 id fName lName mileage 0 “1R67S34” “Graham“ “Greene“ 20000 1 “34TS8R3” “Frederick” “Forsyth” 30000 2 “K2L398D“ “Tom” “Clancy” 4000 3 Search Update 4 5 6 ... ... ... ... 99 Chapters 9 & 10 Arrays & Strings

  26. 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000WMK85S3 Ken Follett 1000 id fName lName mileage 0 “1R67S34” “Graham“ “Greene“ 20000 1 “34TS8R3” “Frederick” “Forsyth” 31000 2 “K2L398D“ “Tom” “Clancy” 4000 3 Update 4 Search 5 6 ... ... ... ... 99 Chapters 9 & 10 Arrays & Strings

  27. 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000WMK85S3 Ken Follett 1000 id fName lName mileage 0 “1R67S34” “Graham“ “Greene“ 22000 1 “34TS8R3” “Frederick” “Forsyth” 31000 2 “K2L398D“ “Tom” “Clancy” 4000 3 4 5 Add new components 6 Search, not found ... ... ... ... 99 Chapters 9 & 10 Arrays & Strings

  28. 34TS8R3 Frederick Forsyth 1000 1R67S34 Graham Greene 2000WMK85S3 Ken Follett 1000 id fName lName mileage 0 “1R67S34” “Graham“ “Greene“ 22000 1 “34TS8R3” “Frederick” “Forsyth” 31000 2 “K2L398D“ “Tom” “Clancy” 4000 3 “WMK85S3” “Ken” “Follet” 1000 4 5 6 ... ... ... ... 99 Chapters 9 & 10 Arrays & Strings

  29. Algorithm • Read customer data into array • Read one new transaction • Process the new transaction • Repeat steps 2 and 3 until the end of the file • Save the updated customer data • Customer ID • A space • First name • A space • Last name • A space • mileage • A new line • Repeat steps 1-8 until the last customer Chapters 9 & 10 Arrays & Strings

  30. Performance • Binary search • Every iteration cuts the size of search by half • Two comparisons per iteration Chapters 9 & 10 Arrays & Strings