CPROG6

C Programming

For definitions of some important terms related to arrays, click here:

ARRAYS AND COMMAND LINE ARGUMENTS

ARRAYS

	Simple variables allocate memory for the storage of a single value of a specified data type (int, char, float, etc.)
	Arrays allows for the storage of multiple values of a single data type.
	Arrays use a single variable name to access those multiple values.

Memory Allocation

int Num; One memory location

Num

Nums[5]; Contiguous memory allocation

Nums[0]

Nums[1]

Nums[2]

Nums[3]

Nums[4]

	Represent a set of values or a list of related objects that is given one name.
	Each item in the array is called an ELEMENT and each element has the same data type.
	Character Arrays hold non-numeric or string data.
	Numeric Arrays hold integer or floating point data.

Numeric/Character Array

char Letters[5]; int Nums[5];

Creating Arrays

Numeric Arrays: Numeric data is stored in Integer or Floating-point arrays.

	int quantity[7];
	float mileage[5];
	float area[12], AmountDue[36];
	int grades[32],
	credits[50],
	hours[25];

Character Arrays: Character or String data is stored in character arrays.

	char Letters[26];
	char day[7][10]; -- an array of strings; 7 strings of 9 characters
	char JobTitle[30][20]; and a Null ( /0 )
	char StudentNames[50][15];

Subscripts

	A subscript is an integer value that is used to reference a specific element in an array.
	An array is called a subscripted variable.
	Each element is referenced by its subscript.
	The first element is numbered zero (0).
	A subscript may not be negative or exceed the size of the array minus one.

Examples of Subscripted Arrays

char day[7][10];

day[0] = “Sunday”;
day[1] = “Monday”;
day[2] = “Tuesday”;
day[3] = “Wednesday”;
…
day[6] = “Saturday”;

Examples

printf("%s", day[3]);

scanf("%s",day[3]);

strcpy(day[3],"noday");

Initializing Data

Data may be assigned to an array when it is declared.

char day[7][10] = {“Sunday”, “Monday”, “Tuesday”,"Wednesday”, “Thursday”, “Friday”, “Saturday”};

float nums[5] = {1.1, 2.3, 94.5, 781.99, 74.3};

Interactive Input

Data may be assigned to an array by prompting the user to enter it at the keyboard.

                            /* load day array */
                            for (i=1; i < 7 ; i++) {
                                  printf(“\nEnter the day: “);
                                  scanf(“%s”, day[i]);
                            }

File Input

Data may be read from a file and loaded into an array.

/*LoadDayArray/

i=0;
while(!feof(fileptr)) { fscanf(fileptr, "%s", day[ i ]);
i = i + 1; /* or i ++ */

Printing an Array

We can verify the contents of an array by printing a copy of the elements

/* Printing Day Array */
for(i = 0; i < 7; i++) {
printf(“\n %s”, day[i]);
}

Computations using Arrays

Very often the values stored within an array need to be included in calculations.

      total = 0;
      for (i = 0; i < 50; i++) {
      total = total + grade[i];
      }
      average = total / 50;

Parallel Arrays

Often your programs will require that a relationship exist between various types of data. Parallel arrays provide a means of associating lists of data together.

char driver[10][10];
float miles[5];

driver

(0) Joan
(1) Bill
(2) Mary
(3) Harvey
(4) Dorothy

miles

(0) 78.2
(1) 100.8
(2) 999.0
(3) 1.0
(4) 0.0

Two-Dimensional Arrays

Two-dimension arrays are useful for representing data in a table format. The array is defined in rows and columns.

	Rows represent a set of values across a table.
	Columns represent a set of values down a table.

Table Example

Creating a 2d Array

Examples of a 2d array declaration are:

int quantity[7][3];
float mileage[3][5];

Example

Command Line Arguments

Providing input arguments to the main() function

Executing your program

DOS

C:\>edit

C:\>edit myfile

Providing input to the program when executing.

UNIX

%vi

%vi myfile

Environments that support “C” provide a method of passing arguments (parameters) to a program when it begins execution.

When main is called it can be called with 2 arguments.

argc - argument count (or the number of command line arguments the program was invoked with).

argv - argument vector ( a pointer to an array of strings that contains one argument per string).

argc/argv Examples

main(int argc, char *argv[ ]) Note: the size of the array argv depends on the value of argc
argv is an array of strings.

	You create a “C” program (myprog) that accepts arguments that represent text file names.
	When you execute your program you include the names of the files.
	Example:

myprog text1.dat text2.dat

                  The value of argc would be 3: arg[0] is myprog
                                                arg[1] is text1.dat
                                                arg[2] is text2.dat

	Environments that support “C” provide a method of passing arguments (parameters) to a program when it begins execution.
	When main is called it can be called with 2 arguments.
	argc - argument count (or the number of command line arguments the program was invoked with).
	argv - argument vector ( a pointer to an array of strings that contains one argument per string).