1. Arrays Declarations CSCI N305
Department of Computer and Information Science, School of Science, IUPUI
CSCI N305
Arrays
Declarations

2. Arrays Array To refer to an element, specify Format:
Group of consecutive memory locations
Same name and type, ex: an array of integers
To refer to an element, specify
Array name
Position number of particular element in the array
Format:
array_name[ position number ]
First element at position 0
n element array named c:
c[ 0 ], c[ 1 ]...c[ n – 1 ]
Example: int my_array[12]
my_array[0]= -45  value stored
Position number must be an integer number or an
integer expression
Example: my_array[1.5]  ERROR!!
my_array[i+j]  valid if i and j are integers
Name of array (Note that all elements of this array have the same name, my_array)
Position number of the element within array my_array
-45 6 72
1543
-89 62 -3 1
6453 78
my_array[0]
my_array[1]
my_array[2]
my_array[3]
my_array[4]
my_array[5]
my_array[6]
my_array[7]
my_array[8]
my_array[9]
my_array[10]
my_array[11]

3. Arrays (cont.) Array elements are like normal variables
my_array[8] = -3;
scanf("%d", &my_array[8]); printf("%d",my_array[8]);
Perform operations in subscript. If x equals 3:
my_array[ ] == my_array[ 3 ] == my_array[ x ]
Declaring Arrays
When declaring arrays, specify
Name
Type of array
Number of elements: arrayType arrayName[numberOfElements];
Examples:
int c[ 100 ]; /* reserve memory sufficient enough to store 100
elements of type integer */
float myArray[ 3284 ];

4. Arrays (cont.)
Declaring multiple arrays of same type: format similar to regular variables
Example: int b[ 100 ], x[ 27 ];
Arrays may be declared to contain other data types
Example: int a[ 100 ];
float b[ 100 ];
char c[ 100 ]; /* Strings are stored by using character arrays */
Example:
#include <stdio.h>
/* a simple program that uses arrays */
main( {
int i, array_int[100];
for (i=0; i<100; i++)
array_int[i]=0;
printf(“element %d: %d\n”, i, array_int[i]); }

5. Arrays (cont.) Initializers
int n[5] = {1, 2, 3, 4, 5};
Example: main() {
int i, a[10]={1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
for (i=0; i<10; i++)
printf(“Element: %d\n”, a[i]); }
If there are fewer initializations than elements in the array, then the remaining elements are automatically initialized to 0.
int n[5] = {0} /* All elements 0 */
int a[10] = {1, 2} /* a[2] to a[9] are initialized to zeros */
int b[5] = {1, 2, 3, 4, 5, 6} /* syntax error */
C arrays have no bounds checking
If size omitted, initializers determine it
int n[ ] = { 1, 2, 3, 4, 5 }; /* 5 initializers, therefore 5 element array */
Scalable Arrays: a better programming style
#define SIZE 10
int c[SIZE]; /* defines a symbolic constant size with value 10 */

6. Arrays (cont.) Example: #include <stdio.h> #define SIZE 100
main() {
int i, a[SIZE];
int sum = 0; …
for (i=0; i < SIZE; i++)
sum = sum + a[i];
printf(“sum: %d\n, sum); }

7. 1. Initialize array 2. Loop 3. Print
1 /* Fig. 6.8: fig06_08.c
2 Histogram printing program */
3 #include <stdio.h>
4 #define SIZE 10 5
6 int main()
7 {
8 int n[ SIZE ] = { 19, 3, 15, 7, 11, 9, 13, 5, 17, 1 };
9 int i, j; 10
11 printf( "%s%13s%17s\n", "Element", "Value", "Histogram" ); 12
13 for ( i = 0; i <= SIZE - 1; i++ ) {
printf( "%7d%13d ", i, n[ i ]) ; 15
for ( j = 1; j <= n[ i ]; j++ ) /* print one bar */
printf( "%c", '*' ); 18
printf( "\n" );
20 } 21
22 return 0;
23 }
1. Initialize array
2. Loop
3. Print
Program output
Element Value Histogram
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