Administrative HW 6 is out ― due next Monday 3/3 @ 9pm

1. Administrative • HW 6 is out ― due next Monday 3/3 @ 9pm • Heads up ― you're writing *3* different programs… • Lab sections are meeting Thurs/Fri as usual • Need help? We have TAs, we have tutors, we have Piazza • Hours and locations: http://www.joehummel.net/cs109.html • Next ― and final ― topic in C++? • Data structures… CS 109 C/C++ Programming for Engineers with MATLAB CS 109 -- 26 Feb 2014

2. Where are we? • Logic skills: • Sequence • Selection • Repetition • Programming skills: • C++ • files • functions • What’s next? • Data structures: • ways to organize data inside the computer… CS 109 -- 26 Feb 2014

3. Motivation — how to model / store data? "apple: a fruit…" "zebra: animal…" "catamaran: a yacht or…" CS 109 -- 26 Feb 2014

4. linear equation 1D array of coefficients DNA two 1D char arrays of DNA "letters" Contacts "John Accrington" 1D array ofstrings "Helen Allsworth" CS 109 -- 26 Feb 2014

5. matrix 2D array of coefficients 2D array of char CS 109 -- 26 Feb 2014

6. 'O' 'X' • Example #1: Tic-Tac-Toe board in C++ • Using variables: • Using a 2D array: #include <iostream> #include <string> using namespace std; . . intmain() { char B11, B12, B13; char B21, B22, B23; char B31, B32, B33; init(B11, B12, B13, …); . . . #include <iostream> #include <string> using namespace std; . . intmain() { char board[3][3]; init(board); . . . CS 109 -- 26 Feb 2014

7. Arrays start at 0, not 1… void init(charboard[3][3]) { board[0][0] = ' '; board[0][1] = ' '; board[0][2] = ' '; board[1][0] = ' '; board[1][1] = ' '; board[1][2] = ' '; board[2][0] = ' '; board[2][1] = ' '; board[2][2] = ' '; } OR void init(char& B11, char& B12, char& B13, char& B21, char& B22, char& B23, char& B31, char& B32, char& B33) { B11 = ' '; // set every position to empty: B12 = ' '; B13 = ' '; B21 = ' '; B22 = ' '; B23 = ' '; B31 = ' '; B32 = ' '; B33 = ' '; } void init(charboard[3][3]) { for (int r=0; r<3; r=r+1) { for (int c=0; c<3; c=c+1) { board[r][c] = ' '; } } } CS 109 -- 26 Feb 2014

8. Example #2: strings in C++ #include <iostream> #include <string> using namespace std; . . intmain() { string s; s = "60605"; if (s[0] == '6') // look at first digit: { cout << "Chicago zip code?"; } A string is a 1D array of characters string object CS 109 -- 26 Feb 2014

9. Arrays: • The most important data structure in Computer Science • Available in all programming languages: C, C++, Java, … • Most programs contain arrays… elements indices Def: an array is a sequence of elements of a single type ― e.g. int, double, or string. Given an array of N elements, their positions are indexedby 0 .. N-1; the [ ] operator is used to access individual elements. intA[100]; // declare an array of 100 elements: for (inti=0; i<100; i=i+1) A[i] = 0; // set element to 0: CS 109 -- 26 Feb 2014

10. for (initial; condition; advance) { . . . } • The For loop: • the For loop is a specialized counting loop // count 0, 1, 2, …, N-1: inti; intN; cin>> N; i = 0; while (i< N) { cout << i; cout << endl; i = i + 1; } // count 0, 1, 2, …, N-1: inti; intN; cin>> N; for (i=0;i< N;i=i+1) { cout << i; cout << endl; } CS 109 -- 26 Feb 2014

11. Example: "vector add" using arrays… • V3 = V1 + V2 // V3 = V1 + V2 int V1[N]; int V2[N]; int V3[N]; . . // fill vectors V1, V2: . for(inti=0; i<N; i=i+1) { V3[i] = V1[i] + V2[i]; } V1 V2 V3 inti; i = 0; while(i < N) { V3[i] = V1[i] + V2[i]; i = i + 1; } CS 109 -- 26 Feb 2014

12. VectorAdd function: #include <iostream> . . . #define N 100 // // V3 = V1 + V2 // void VectorAdd(int V3[N], int V1[N], int V2[N]) { for (inti=0; i<N; i=i+1) { V3[i] = V1[i] + V2[i]; } } intmain() { int V1[N], V2[N], V3[N]; . . . VectorAdd(V3, V1, V2);