1. Computer Programming Lecture 14 Arrays (Part 2)
Assist.Prof.Dr. Nükhet ÖZBEK
Ege University
Department of Electrical & Electronics Engineering

2. Topics The relationship between pointers and arrays
Multi-dimensional arrays
Passing multi-dimensional arrays to functions

3. The relationship between pointers and arrays
Arrays and pointers are intimately related in C and may be used almost interchangeably
An array name can be thought as a constant pointer
Pointers can be used to do any operation involving array subscripting

4. The relationship between pointers and arrays
Assume an integer array b[5] and integer pointer bPtr
The following expressions are equivalent
bPtr = b; ≡ bPtr = &b[0];
b[3] ≡ *(bPtr + 3)
&b[3] ≡ bPtr + 3
b[3] ≡ *(b + 3)
b[3] ≡ bPtr[3]

5. The relationship between pointers and arrays
Good programming practice
Use array notation instead of pointer notation

6. Multi-dimensional Arrays
Each element of an array is like a single item of a particular type
But an array itself is an item of a particular type So, an array element could be another array
An “array-of-arrays” is called “multi-dimensional” (or “multi-subscripted”) because you need to specify more than one ordinate to locate an actual element

7. Multidimensional Array Declaration
data_type arrayname[size1][size2]…[sizen];
Examples
double table[NROWS][NCOLS];
int array[7][5][6];

8. Initialization of Multidimensional Arrays
You can initialize multidimensional arrays like one-dimensional array
However, instead of listing all table values in one list, the values are usually grouped by rows
Example
int table[3][3] = {
{1,2,3},{4,5,6},{7,8,9} };

9. Example: YearlyRainfall
month
year
Average Yearly Rainfall (in mm)
Problem: using the Yearly Rainfall table
input month and year
output mean rainfall for that month and year

10. Example (cont): YearlyRainfall-1
#define NYEARS 5
#define NMONTHS 12
int lookup(int year, int month) {
int table[NYEARS][NMONTHS] =
{30,40,75,95,130,220,210,185,135,80,40,45},
{25,25,80,75,115,270,200,165, 85, 5,10, 0},
{35,45,90,80,100,205,135,140,170,75,60,95},
{30,40,70,70, 90,180,180,210,145,35,85,80},
{30,35,30,90,150,230,305,295, 60,95,80,30} };
if ((0 <= year) && (year < NYEARS) &&
(0 <= month) && (month < NMONTHS))
return table[year][month]; }
else
return -1;
yearly1.c

11. Example (cont): YearlyRainfall-1
int main() {
int year;
int month;
int rainfall;
printf("Enter year and month: ");
scanf("%d %d", &year, &month);
rainfall = lookup(year - 1, month - 1);
if (rainfall < 0)
printf("Year must be between 1 and %d,\n", NYEARS);
printf("and month must be between 1 and %d.\n", NMONTHS); }
else
printf("Rainfall for year %d, month %d is %d mm.\n",
year, month, rainfall);
return 0;
yearly1.c

12. Example (cont): YearlyRainfall-1
#define NYEARS 5
#define NMONTHS 12
int lookup(int year, int month) {
int table[NYEARS][NMONTHS] =
{30,40,75,95,130,220,210,185,135,80,40,45},
{25,25,80,75,115,270,200,165, 85, 5,10, 0},
{35,45,90,80,100,205,135,140,170,75,60,95},
{30,40,70,70, 90,180,180,210,145,35,85,80},
{30,35,30,90,150,230,305,295, 60,95,80,30} };
if ((0 <= year) && (year < NYEARS) &&
(0 <= month) && (month < NMONTHS))
return table[year][month]; }
else
return -1;
yearly1.c

13. Example (cont) : YearlyRainfall-1
#define NYEARS 5
#define NMONTHS 12
int lookup(int year, int month) {
int table[NYEARS][NMONTHS] =
{30,40,75,95,130,220,210,185,135,80,40,45},
{25,25,80,75,115,270,200,165, 85, 5,10, 0},
{35,45,90,80,100,205,135,140,170,75,60,95},
{30,40,70,70, 90,180,180,210,145,35,85,80},
{30,35,30,90,150,230,305,295, 60,95,80,30} };
if ((0 <= year) && (year < NYEARS) &&
(0 <= month) && (month < NMONTHS))
return table[year][month]; }
else
return -1;
yearly1.c

14. Example (cont): YearlyRainfall-1
int main() {
int year;
int month;
int rainfall;
printf("Enter year and month: ");
scanf("%d %d", &year, &month);
rainfall = lookup(year - 1, month - 1);
if (rainfall < 0)
printf("Year must be between 1 and %d,\n", NYEARS);
printf("and month must be between 1 and %d.\n", NMONTHS); }
else
printf("Rainfall for year %d, month %d is %d mm.\n",
year, month, rainfall);
return 0;
yearly1.c

15. Example (cont): YearlyRainfall-2
int main() {
int year;
int month;
int rainfall;
printf("Enter year and month: ");
scanf("%d %d", &year, &month);
rainfall = lookup(year - 1, month - 1);
if (rainfall < 0)
printf("Year must be between 1 and %d,\n", NYEARS);
printf("and month must be between 1 and %d.\n", NMONTHS); }
else
printf("Rainfall for year %d, month %d is %d mm.\n",
year, month, rainfall);
return 0;
yearly1.c

16. Example (cont): YearlyRainfall-2
int main() {
int year;
int month;
int rainfall;
printf("Enter year and month: ");
scanf("%d %d", &year, &month);
rainfall = lookup(year - 1, month - 1);
if (rainfall < 0)
printf("Year must be between 1 and %d,\n", NYEARS);
printf("and month must be between 1 and %d.\n", NMONTHS); }
else
printf("Rainfall for year %d, month %d is %d mm.\n",
year, month, rainfall);
return 0;
yearly1.c

17. Example: 3-D Array
Page 4
Page 3
Page 2
Page 1

18. Example 1: 3-D Array - 1 multid1.c #include <stdio.h>
#define NROWS 3
#define NCOLS 5
#define NPAGES 2
int main() {
float ledger[NPAGES][NROWS][NCOLS];
int page, row, column;
/* Fill in the multi-d array with values */
for (page=0; page < NPAGES; page++)
{ for (row=0; row < NROWS; row++)
{ for (column=0; column < NCOLS; column++)
ledger[page][row][column]) =
page + (row / 10.0) + (column / 100.0); }
/* Print out the values in the multi-d array */
{ printf("%10.2f", ledger[page][row][column]);
printf("\n");
return 0;
multid1.c

19. Example 1 (cont): 3-D Array-1
#include <stdio.h>
#define NROWS 3
#define NCOLS 5
#define NPAGES 2
int main() {
float ledger[NPAGES][NROWS][NCOLS];
int page, row, column;
/* Fill in the multi-d array with values */
for (page=0; page < NPAGES; page++)
for (row=0; row < NROWS; row++)
for (column=0; column < NCOLS; column++)
ledger[page][row][column]) =
page + (row / 10.0) + (column / 100.0); }
multid1.c

20. Example 1 (cont): 3-D Array-1
/* Print out the values in the multi-d array */
for (page=0; page < NPAGES; page++) {
for (row=0; row < NROWS; row++)
for (column=0; column < NCOLS; column++)
printf("%10.2f", ledger[page][row][column]); }
printf("\n");
return 0;
multid1.c

21. Passing Multi-Dimensional Arrays to Functions
In the function definition, the size of the array needs to be specified
Any changes to array elements within the function affect the “original” array elements

22. Example 2: 3-D Array-2 multid2.c #include <stdio.h>
#define NROWS 3
#define NCOLS 5
#define NPAGES 2
void inputEntry(float ledger[][NROWS][NCOLS]);
void printTables(float ledger[NPAGES][NROWS][NCOLS]);
int main() {
float ledger[NPAGES][NROWS][NCOLS] = {{{0}}};
printTables(ledger);
while (1)
inputEntry(ledger); }
return 0;
multid2.c

23. Example 2 (cont): 3-D Array-2
#include <stdio.h>
#define NROWS 3
#define NCOLS 5
#define NPAGES 2
void inputEntry(float ledger[][NROWS][NCOLS]);
void printTables(float ledger[NPAGES][NROWS][NCOLS]);
int main() {
float ledger[NPAGES][NROWS][NCOLS] = {{{0}}};
printTables(ledger);
while (1)
inputEntry(ledger); }
return 0;
multid2.c

24. Example 2 (cont): 3-D Array-2
/* Reads in a location in the ledger and the value of one item to be put in the ledger */
void inputEntry ( float ledger[][NROWS][NCOLS] ) {
int page, row, column;
printf("Enter page, row and column number: ");
scanf("%d %d %d", &page, &row, &column);
if ((0 <= page && page < NPAGES) &&
(0 <= row && row < NROWS) &&
(0 <= column && column < NCOLS))
printf("Enter value: ");
scanf("%f", &ledger[page][row][column]); }
else
printf("Invalid entry location. No change.\n");
multid2.c

25. Example 2 (cont): 3-D Array-2
/* Reads in a location in the ledger and the value of one item to be put in the ledger */
void inputEntry ( float ledger[][NROWS][NCOLS] ) {
int page, row, column;
printf("Enter page, row and column number: ");
scanf("%d %d %d", &page, &row, &column);
if ((0 <= page && page < NPAGES) &&
(0 <= row && row < NROWS) &&
(0 <= column && column < NCOLS))
printf("Enter value: ");
scanf("%f", &ledger[page][row][column]); }
else
printf("Invalid entry location. No change.\n");
multid2.c

26. Example 2 (cont): 3-D Array-2
/* Reads in a location in the ledger and the value of one item to be put in the ledger */
void inputEntry ( float ledger[][NROWS][NCOLS] ) {
int page, row, column;
printf("Enter page, row and column number: ");
scanf("%d %d %d", &page, &row, &column);
if ((0 <= page && page < NPAGES) &&
(0 <= row && row < NROWS) &&
(0 <= column && column < NCOLS))
printf("Enter value: ");
scanf("%f", &ledger[page][row][column]); }
else
printf("Invalid entry location. No change.\n");
multid2.c

27. Example 2 (cont): 3-D Array-2
/* Reads in a location in the ledger and the value of one item to be put in the ledger */
void inputEntry ( float ledger[][NROWS][NCOLS] ) {
int page, row, column;
printf("Enter page, row and column number: ");
scanf("%d %d %d", &page, &row, &column);
if ((0 <= page && page < NPAGES) &&
(0 <= row && row < NROWS) &&
(0 <= column && column < NCOLS))
printf("Enter value: ");
scanf("%f", &ledger[page][row][column]); }
else
printf("Invalid entry location. No change.\n");
multid2.c

28. Example 2 (cont): 3-D Array-2
/* Prints the ledger page-by-page, and each page
row-by-row */
void printTables ( float ledger[NPAGES][NROWS][NCOLS] ) {
int page, row, column;
for (page=0; page < NPAGES; page++)
for (row=0; row < NROWS; row++)
for (column=0; column < NCOLS; column++)
printf("%10.2f", ledger[page][row][column]); }
printf("\n");
multid2.c

29. Example 2 (cont): 3-D Array-2
/* Prints the ledger page-by-page, and each page
row-by-row */
void printTables ( float ledger[NPAGES][NROWS][NCOLS] ) {
int page, row, column;
for (page=0; page < NPAGES; page++)
for (row=0; row < NROWS; row++)
for (column=0; column < NCOLS; column++)
printf("%10.2f", ledger[page][row][column]); }
printf("\n");
multid2.c

30. Notes
ANSI C requires that an implementation allow multidimensional arrays of at least six dimensions

31. fig06_07.c (Part 1 of 2)

32. fig06_07.c (Part 2 of 2) Program Output
Rating Frequency

33. fig06_08.c (Part 1 of 2)

34. fig06_08.c (Part 2 of 2) Program Output
Element Value Histogram
*******************
***
***************
*******
***********
*********
*************
*****
***************** *
fig06_08.c (Part 2 of 2) Program Output

35. fig06_10.c (Part 1 of 2)

36. fig06_10.c (Part 2 of 2) Enter a string: Hello there string1 is: Hello
string2 is: string literal
string1 with spaces between characters is:
H e l l o
fig06_10.c (Part 2 of 2)

37. fig06_15.c (Part 1 of 3)

38. fig06_15.c (Part 2 of 3)

39. fig06_15.c (Part 3 of 3) Program Output
Data items in original order
Data items in ascending order
fig06_15.c (Part 3 of 3) Program Output

40. fig06_16.c (Part 1 of 8)

41. fig06_16.c (Part 2 of 8)

42. fig06_16.c (Part 3 of 8)

43. fig06_16.c (Part 4 of 8)

44. fig06_16.c (Part 5 of 8)

45. fig06_16.c (Part 6 of 8)

46. fig06_16.c (Part 7 of 8)

47. fig06_16.c (Part 8 of 8)

48. Program Output ******** Mean The mean is the average value of the data
items. The mean is equal to the total of
all the data items divided by the number
of data items ( 99 ). The mean value for
this run is: 681 / 99 =
Median
The unsorted array of responses is
The sorted array is
Program Output

49. Program Output (continued)
The median is element 49 of
the sorted 99 element array.
For this run the median is 7
********
Mode
Response Frequency Histogram *
***
****
*****
********
*********
***********************
***************************
*******************
The mode is the most frequent value.
For this run the mode is 8 which occurred 27 times.

50. fig06_18.c (Part 1 of 3)

51. fig06_18.c (Part 2 of 3)

52. fig06_18.c (Part 3 of 3) Program Output
Enter integer search key: 36
Found value in element 18 37
Value not found

53. fig06_19.c (Part 1 of 5)

54. fig06_19.c (Part 2 of 5)

55. fig06_19.c (Part 3 of 5)

56. fig06_19.c (Part 4 of 5)

57. fig06_19.c (Part 5 of 5)

58. Program Output Enter a number between 0 and 28: 25 Subscripts:
Subscripts: * *
24 26* 28
24*
 25 not found
Enter a number between 0 and 28: 8
 Subscripts: *
8 10* 12 8*
 8 found in array element 4
Program Output

59. Enter a number between 0 and 28: 6 Subscripts:
Subscripts: * *
 6 found in array element 3