Arrays in C

Intro to Arrays

Storing List of Data

Why Arrays

Suppose we want to store the grade of each student in a class

Need a varitable for each?

int bod, mary, tom, ...;

Easier to have a variable that stores the grandes for all students

Arrays in C

An array is a "Chunk of memory"

An array is a contiguous piece of memory that can contain multiple values

The values within the contiguous chunk can be addressed individually

Address in memory	0x7f340	0x7f344	0x7f348	0x7f34c	0x7f350	0x7f354	0x7f358	0x7f35c	0x7f360
Grades	74	59	95	85	71	45	99	82	76

Arrays in C

Array: "Chunk of memory"

Physycal address	0x7f340	0x7f344	0x7f348	0x7f34c	0x7f350	0x7f354	0x7f358	0x7f35c	0x7f360
Grades	74	59	95	85	71	45	99	82	76
index	0	1	2	3	4	5	6	7	8

Use an index to access individual elements of the array: grades[0] is 74, grades[1] is 59, grades[2] is 95, and so on

Arrays in C

Array Declaration

Syntax for declaring array variable:

type array_name[capacity]

Type can be any type (int, float, char, ...)

array_name is an identifier

Capacity is the number of values it can store (indexing starts at 0)

Arrays in C

Example Arrays

int x[3]; //an array of 3 integers
double y[7]; //an array of doubles

Arrays in C

Operations with Arrays

Assigment

x[0] = 6; //Assign 6 to element x[0]
y[2] = 3.1; //Assign 3.1 to element y[2]

Access

m = x[2];
p = y[0];

Input/Output

The elements are handled as their types, e.g

scanf("%d %ld", &x[2], &y[3]);
printf("%d %lf\n", x[0], y[2]); //output 6 and 3.1

Arrays in C

Arithmetic Operations

void main(){
	double x[5];
	x[0] = 1;
	x[1] = 2;
	x[2] = x[0] + x[1];
	x[3] = x[2] / 2;
	x[4] = x[3] * x[2];
}

Arrays in C

For loops

"for" loops are ideal for processing elements in the array

int i;
double values[] = {3.14, 1.0, 2.61, 5.3};
double sumValues = 0.0;
for( i = 0; i < 4; i++){
	sumValues += values[i];
}
printf("%lf\n", sumValues);

Arrays in C

Initialization

Systax: int a[] = {2, 4, 7, 9}

Behavior: initialize elements starting with leftmost i.e: element 0. Remaining elements are initialized to zero

X	2	4	7	9
	0	1	2	3

Initialize all to 0: int x[4] = { 0 };

Arrays in C

Constants for capacity

Good programming practice:

use #define for constants in you program

For example:

#define MAX_LIMIT 25
int grades[MAX_LIMIT];
for(int i = 0; i < MAX_LIMIT; i++){
}

If size need to be changed, only the capacity "MAX_LIMIT" needs to be changed

Arrays in C

Arrays as parameters of functions

double sumValues(double x[], int numElements){
	double result = 0;
	for(int i = 0; i < numElements; i++){
		result += result + x[i];
	}
	return result;
}
void main(){
	double values[] = { 3.14, 1.0, 2.61, 5.3 };
	printf("Sum = %lf\n", sumValues(values, 4));
}

"[]" flags the parameters as an array

Always passed by reference

Array size is passed separately (as numElements)

Arrays in C

Example

Program Behavior

Create an array of random numbers
Print unsorted array
Sort the array
Print sorted array

Arrays in C

Example

void randomArray(double elements[], int numElements);
void printArray(double elements[], int numElements);
void sortArray(double elements[], int numElements);
void swap(double a, double b);