Wednesday, 11/6/02, Slide #1 CS 106 Intro to CS 1 Wednesday, 11/6/02  QUESTIONS?? – HW # 4 due Monday  Today:  Return HW #3  Arrays (Chap. 10)  Reading: 10.1  Exercises: p. 252 ff, 1, 11, 12  New files/handouts: Array1.cpp

Wednesday, 11/6/02, Slide #2 Chapter 10: Arrays  Most (but not all) of our object types so far have been simple types  Each object represents a single value  Examples: int, float, char, double  C++ also has structured data types  Each object represents a collection of values  Examples: ifstream, ofstream, string  Examples: Class objects like Complex, Currency Some operations to deal with entire object; others access individual parts of it

Wednesday, 11/6/02, Slide #3 Example: Processing lists of data  Suppose we have 25 grades and want to perform the tasks shown below. In each case, how many objects need to be held in memory (not just processed) to perform the task?  Compute the average (mean)  Compute the median  Find the highest grade  Print out all grades after they have all been inputted

Wednesday, 11/6/02, Slide #4 Average (Mean) and Highest  These just process the data. They don't need a separate object for each grade: float Sum = 0; for (int i = 1; i <= 25; ++i) {cin >> Grade; Sum += Grade; } float Average = Sum / 25;  The single object Grade is used for all the grade values (Highest similar).

Wednesday, 11/6/02, Slide #5 Median and Print Whole List  For these we need to remember all the grades -- so we need 25 objects (i.e., 25 different memory locations, each holding one grade)!  The C++ Array structure is a way of storing a list of objects together,  Using a single name for the whole list,  Using an index (0 to 24 for 25 objects) to refer to individual elements in the list.

Wednesday, 11/6/02, Slide #6 Declaring arrays; diagram of memory  char C[4];  const int N = 6; float A[N];  Number in array declaration must be a constant.  Array index (or subscript) goes from 0 to N-1 (not from 1 to N).  A[k] is the name of the k th item in array. A[0] A[1] A[2] A[3] A[4] A[5] A[0] A[1] A[2] A[3] A[4] A[5] C[0] C[1] C[2] C[3] C[0] C[1] C[2] C[3] ‘x’ ‘4’ ‘&’ ‘Y’

Wednesday, 11/6/02, Slide #7 Using array elements (Array1.cpp) double A[6]; A[4] = 341.0; A[2] = A[4] + 1.5; cout << A[2]; int j = 2; cin >> A[j + 1]; cout << A[j + 4]; A[0] A[1] A[2] A[3] A[4] A[5] A[0] A[1] A[2] A[3] A[4] A[5] A[] Warning! Index is out of range!

Wednesday, 11/6/02, Slide #8 Initializing Small Arrays  The elements of arrays declared locally are not given initial values.  For small arrays, we can initialize when we declare as follows: int Val[5] = {17, 36, 92, 14, -10}; int Val[5] = {17, 36, 92, 14, -10}; char Vowels[ ] = {'a', 'e', 'i', 'o', 'u‘, ‘y’}; char Vowels[ ] = {'a', 'e', 'i', 'o', 'u‘, ‘y’};  To process large arrays, we'll need to use loops! Number of elements supplied determines size of array

Wednesday, 11/6/02, Slide #9 Initializing Large Arrays  A simple way to initialize a large (or small) array of size N is to use a for-loop that increments the index from 0 to N-1: //Declare an array of numbers, //Initialize all values to 0 const int Length = 50; double dArray[Length]; for (int i = 0; i < Length; ++i) {dArray[i] = 0; } Notice that i starts at 0 (not 1!) and stops before Length (not at Length)