Csc1100 lecture09 ch07_pt2

A First Book of C++A First Book of C++
Chapter 7 (Pt 2)Chapter 7 (Pt 2)
ArraysArrays

∗ In this chapter, you will learn about:
∗ One-Dimensional Arrays
∗ Array Initialization
∗ Arrays as Arguments
∗ Two-Dimensional Arrays
∗ Common Programming Errors
∗ Searching and Sorting Methods
A First Book of C++ 4th Edition 2
Objectives

∗ Two-dimensional array (table): consists of both
rows and columns of elements
∗ Example: two-dimensional array of integers
col[0] col[1] col[2] col[3]
row[0] 8 16 9 5
row[1] 3 15 27 6
row[2] 14 25 2 10
∗ Array declaration: names the array val and
reserves storage for it
int val[2][2];
row colA First Book of C++ 4th Edition 3
Two-Dimensional Arrays
array val with 2 cols and 2 rows
row 0
row 1
col 0 col 1

∗ Locating array elements (Figure 7.7)
∗ val[1][3] uniquely identifies element in row 1, column 3
∗ Examples using elements of val array:
// assign value in row 2, col 3 into variable price
price = val[2][3];
val[0][0] = 62;//assign 62 to row 0, col 0
newnum = 4 * (val[1][0] - 5);
sumRow = val[0][0] + val[0][1] + val[0][2] +
val[0][3];
∗ The last statement adds the elements in row 0 and sum is
stored in sumRow
Two-Dimensional Arrays (cont'd.)

∗ Initialization: can be done within declaration
statements (similar to single-dimension arrays)
∗ Example:
int val[3][4] = { {8,16,9,52},
{3,15,27,6},
{14,25,2,10} };
∗ First set of internal braces contains values for row 0,
second set for row 1, and third set for row 2
∗ Commas in initialization braces are required; inner
braces can be omitted
col 0 1 2 3
row
0
1
2

∗ Processing two-dimensional arrays:
∗ nested for loops are typically used
∗ Easy to cycle through each array element
∗ A pass through outer loop corresponds to a row
∗ A pass through inner loop corresponds to a column
∗ Nested for loop in Program 7.7 used to multiply each val
element by 10 and display results
∗ Output of Program 7.7
Display of multiplied elements
80 160 90 520
30 150 270 60
140 250 20 100

∗ Prototypes for functions that pass two-dimensional
arrays can omit the row size of the array
∗ Example (Program 7.8): optional
display (int [ ][4]);
∗ Row size is optional, but column size is required
∗ Assuming 4 bytes for an int, the element val[1][3] is
located 28 bytes from the start of the array (i.e., offset)

∗ Determining offset of an array (val [1][3])
∗ Computer uses row index, column index, and column
size to determine offset
3+1

4 bytes 4 bytes 4 bytes 4 bytes
4 bytes 4 bytes 4 bytes

∗ Arrays with more than two dimensions allowed in C++ but
not commonly used
∗ Example: int response[4][10][6]
∗ First element is response[0][0][0]
∗ Last element is response[3][9][5]
∗ A three-dimensional array can be viewed as a book of data
tables (Figure 7.10)
∗ First subscript (rank) is page number of table
∗ Second subscript is row in table
∗ Third subscript is desired column
Larger Dimensional Arrays

Larger Dimensional Arrays
(cont'd.)

∗ Forgetting to declare an array
∗ Results in a compiler error message equivalent to “invalid
indirection” each time a subscripted variable is
encountered within a program
∗ Using a subscript that references a nonexistent array
element (exceeding declared size/index)
∗ For example, declaring array to be of size 20 (e.g, int
val[20])and using a subscript value of 25 (e.g,
val[25])
∗ Not detected by most C++ compilers and will probably
cause a runtime error
Common Programming Errors

∗ Not using a large enough counter value in a for loop
counter to cycle through all array elements
∗ Forgetting to initialize array elements
∗ Don’t assume compiler does this.
∗ Example:
val [8] = 60; // initialize or assign value to your array element
Common Programming Errors
(cont'd.)

∗ One-dimensional array: a data structure that stores a
list of values of same data type
∗ Must specify data type and array size
∗ Example:
int num[100]; //creates an array of 100 integers
∗ Array elements are stored in contiguous locations (in
sequence) in memory and referenced using the array
name and a subscript
∗ Example: values[4]
∗ means access the 5th
element of the
values array at index 4
Summary

∗ Two-dimensional array is declared by listing both a
row and column size with data type and name of
array
∗ Arrays may be initialized when they are declared
∗ For two-dimensional arrays, you list the initial values, in
a row-by-row manner, within braces and separating
them with commas
∗ Arrays are passed to a function by passing name of
array as an argument (to be discussed in next class)
Summary (cont'd.)

∗ Most programmers encounter the need to both sort
and search a list of data items at some time in their
programming careers
Chapter Supplement: Searching
and Sorting Methods

∗ Linear (sequential) search
∗ Each item in the list is examined in the order in which it
occurs until the desired item is found or the end of the
list is reached
∗ List doesn’t have to be in sorted order to perform the
search
∗ Binary search
∗ Starting with an ordered list, the desired item is first
compared with the element in the middle of the list
∗ If item is not found, you continue the search on either
the first or second half of the list
Search Algorithms

Csc1100 lecture09 ch07_pt2

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Csc1100 lecture09 ch07_pt2