2D Arrays

1
2D Arrays
Alina Solovyova-Vincent Department of Computer
Science Engineering University of Nevada,
Reno Spring 2006
2
Declarations

• datatype array_name num_of_rows num_of_col
• int array_11010 // indexed from (0,0) to
  (9,9)
• char array_234 //indexed from (0,0) to
  (2,3)
• float array_3210 //indexed from (0,0) to
  (1,9)

The first index always indicates the row, the
second the column.
3
Declarations

• char letters34
• or
• const int row 3const int col 4char
  lettersrowcol //preferred way

4
1-D vs. 2-D Arrays
0,0 0,1 0,2 0,3 0,4
1,0 1,1 1,2 1,3 1,4
2,0 2,1 2,2 2,3 2,4
3,0 3,1 3,2 3,3 3,4
4,0 4,1 4,2 4,3 4,4
0
1
2
3
4
5
int table43

• 72 45 1562 10 019 99 2738 24 89

table22
6
Examples

• float array_A122
• char array_B73
• int array_C410

7
Row-Major Order

• 72 45 1562 10 019 99 2738 24 89
• 72451562100199927382489 ? ?

8
Initialization

• int nums34 2,4,6,8,1,3,5,7,5,2,7,10
• int nums34 2,4,6,8,
• 1,3,5,7,
• 5,2,7,10
• int nums34 2,4,6,8,
• 1,3,5,7,
• 5,2,7,10

9
Accessing All Elements of an Array

• for ( i 0 i lt row i )
• for( j0 jltcolumn j ) cout ltlt
  bunch_of_numsij ltlt \t
• cout ltlt endl

10
Accessing Individual Elements

• int numint bunch_of_nums1010bunch_of_n
  ums00 25num bunch_of_nums35

11
Using Subscript Expressions

• result result value i 2 i num
• cout ltlt num i row col-6

12
Worksheet

• Declare an array to store 5x5 matrix of integers.
  
• List all of the elements on the major diagonal.
• List all of the elements on the minor diagonal.
• Write a code segment that would display all of
  the elements on the major diagonal.
• Write a code segment that would display all of
  the elements on the minor diagonal.

13

• const int size 5
• int squaresizesize
• // display major diagonal in one loop
• for (int i 0 i lt size i)
• cout ltlt squareii ltlt endl
• // display minor diagonal in one loop
• for (int i 0 i lt size i)
• cout ltlt squareisize-1-i ltlt endl

14

• const int size 5
• int squaresizesize
• // display major diagonal in two loops
• for (int i 0 i lt size i)
• for (int j 0 j lt size j)
• if (i j)
• cout ltlt squareij ltlt endl
• // display minor diagonal in two loops
• for (int i 0 i lt size i)
• for (int j 0 j lt size j)
• if (i j size-1)
• cout ltlt squareij ltlt endl

15
Worksheet

• Write a code segment that declares
• 45 x 33 array of integers and initializes
  all elements to 0. The program should then prompt
  the user for a location in that array ( row
  number, column number) and tell the user whether
  its a valid location ( i.e. within bounds). For
  example (4, 16) is a valid, (-3, 5) is invalid,
  (13, 56) is invalid. If location is valid,
  display the contents of that location.

16

• const int nrow 45
• const int ncol 33
• int arrnrowncol 0
• do
• cout ltlt "Enter row and column "
• cout ltlt r ltlt c
• while (r lt 0 r gt nrow
• c lt 0 c gt ncol)
• cout ltlt "The element in ("
• ltlt r ltlt ", " ltlt c ltlt ") is "
• ltlt arrrc

17
2-D Arrays in Functions

• void ProcessValues (int 5, int, int)
• //works with ALL 2-d arrays that have
• // exactly 5 columns i.e. 10x5, 2x5 .

18

• int max(int 2, int, int)
• void main()
•    const int nrow 4, ncol 2    int
  numsnrowncol 3,2,5,13,1,7,9,4
•  cout ltlt "The max value of the array is "
• ltlt max(nums, nrow , ncol)
• int max(int vals 2, int nr, int nc)
•    int i, j, max vals00
• for (i 0 i lt nr i)       for (j 0
  j lt nc j)          if (max lt valsij)
               max valsij
• return max

19
Worksheet

• Write a function that receives an array of
  floating point values, number of rows and number
  of columns (known to be 7) in that array, and a
  special number between 0 and 6. The function
  should return the sum of all elements in the
  column that corresponds to the special number.