Arrays

An array is a collection of data storage locations
Each location has the same data type and name
For example each months monthly expenses can be represented as expenses[1], expenses[2], ... instead of using a different variable name, where [1] in expenses[1] is called the subscript.
note that the first element in the array is expenses[0] but not expenses[1]

Declaration :  
float expenses[12];

Initialization:
expenses[11] = 87.90;
expenses[11] = expenses[10];
expenses[2+3] = 100;
i = 4; 
expenses[i] = 100;
int a[6];
a[2] = 2;
expenses[a[2]] = 100;

#define MONTHS 12
int expenses[MONTHS];

int MONTHS =  12;
int expenses[MONTHS]; (is not correct)

Initialization with Declaration:
int a[4] = { 100, 200, 300, 400};
int a[] = { 100, 200, 300, 400};
int a[4] = { 100, 200, 300};
int a[4] = { 100, 200, 300, 400, 500}; (not correct)

Example:
#include <stdio.h>
void main()
{
  /* Declare an array to hold expenses, and a counter variable */
  float expenses[13];
  int count;
  /* Input data from keyboard into array */
  for (count = 1; count < 13; count++)
  {
    printf("Enter expenses for month %d: ", count);
    scanf("%f", &expenses[count]);
  }
  /* Print array contents */
  for (count = 1; count < 13; count++)
  {
    printf("\nMonth %d = $%.2f", count, expenses[count]);
  }
}

An array may have multiple dimensions. E.g. Two dimensional array : int cell[4][3];
C places no limit on the number of dimensions in an array

int cell[4][3] = {1,2,3,4,5,6,7,8,9,10,11,12};
int cell[4][3] = { {1,2,3}, {4,5,6}, {7,8,9}, {10,11,12} };

Example:
#include <stdio.h>
#include <stdlib.h>
void main()
{
  /* Declare a three-dimensional array with 1000 elements */
  int random_array[10][10][10];
  int a, b, c;
  /* Fill the array with random numbers. The C library */
  /* function rand() returns a random number. Use one */
  /* for loop for each array subscript. */
  for (a = 0; a < 10; a++)
  {
    for (b = 0; b < 10; b++)
    {
      for (c = 0; c < 10; c++)
      {
        random_array[a][b][c] = rand();
      }
    }
  }
  /* Now display the array elements 10 at a time */
  for (a = 0; a < 10; a++)
  {
    for (b = 0; b < 10; b++)
    {
      for (c = 0; c < 10; c++)
      {
        printf("\nrandom_array[%d][%d][%d] = ", a, b, c);
        printf("%d", random_array[a][b][c]);
      }
      printf("\nPress a key to continue, CTRL-C to \
        quit.");
      getchar();
    }
  }
}        /* end of main() */
Example:
/* Demonstrates the sizeof() operator */
#include <stdio.h>
void main()
{
  /* Declare several 100 element arrays */
  int intarray[100];
  float floatarray[100];
  double doublearray[100];
  /* Display the sizes of numeric data types */
  printf("\n\nSize of int = %d bytes", sizeof(int));
  printf("\nSize of short = %d bytes", sizeof(short));
  printf("\nSize of long = %d bytes", sizeof(long));
  printf("\nSize of float = %d bytes", sizeof(float));
  printf("\nSize of double = %d bytes", sizeof(double));
  /* Display the sizes of the three arrays */
  printf("\nSize of intarray = %d bytes", sizeof(intarray));
  printf("\nSize of floatarray = %d bytes",
    sizeof(floatarray));
  printf("\nSize of doublearray = %d bytes",
    sizeof(doublearray));
}

Character Strings

A character is a single letter, numeral, punctuation mark, or any such symbol
a string is any sequence of characters
char type is used to hold characters
How does a computer memory hold characters? Each character is represented as a numerical value in ASCII code
ASCII code assigns values between 0-255 for upper and lower case, numeric digits, punctuation marks and any other symbols. E.g. ``97'' is used to represent ``a''
Thus a char is actually a numeric integer data type
If a char variable is used where a character is expected, it is interpreted as a character
If a char variable is used where a number is expected, it is interpreted as a number

Character Variables:

char a, b, c;
char code = 'x';
code = '!';

Character Constants:

#define EX 'x'
char code = EX

Example 1:
/* Demonstrates the numeric nature of char variables */
#include <stdio.h>
int main()
{
  /* Declare and initialize two char variables */
  char c1 = 'a';
  char c2 = 90;
  /* Print variable c1 as a character then as a number */
  printf("\nAs a character, variable c1 is %c", c1);
  printf("\nAs a number, variable c1 is %d", c1);
  /* Do the same for variable c2 */
  printf("\nAs a character, variable c2 is %c", c2);
  printf("\nAs a number, variable c2 is %d", c2);
  return 0;
}

char goes only upto 127. char is used to represent all letters, numbers, punctuation marks, and keyboard symbols
the remaining (i.e. from 128-255) are used to represent special characters such as foreign letters, graphical symbols.
unsigned char must be used for these characters.

Example 2:
/* Demonstrates printing extended ASCII characters */
#include <stdio.h>
int main()
{
  unsigned char x;  /* Must be unsigned for extended ASCII */
  /* Print extended ASCII characters 180 through 203 */
  for (x = 180; x < 204; x++)
  {
    printf("\nASCII code %d is character %c", x, x);
  }
  return 0;
}

Character Strings

Often, we nee to store a sequence of characters such as name, address etc.
character strings can be stored using an array of characters
To store a name with 9 characters, we must use an array with 10 elements (char name[10];)
the last element is used to store a special character ``null'' represented as \0.
If the null character is missing, the program thinks that the string extends until the next null character in memory.

char name[10] = {'C', 'o', 'm', 'p', 'u', 't', 'e', 'r', 's', '\0'};
char name[10] = ``Computers'';
char name[] = ``Computers'';

About this document ...

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latex2html -split 0 -html_version 3.0 c4.tex.

The translation was initiated by Vijay & on Thu Feb 19 11:47:48 EST 1998

Vijay &
Thu Feb 19 11:47:48 EST 1998