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 memory0x7f3400x7f3440x7f3480x7f34c0x7f3500x7f3540x7f3580x7f35c0x7f360
Arrays in C

Array: "Chunk of memory"

Physycal address0x7f3400x7f3440x7f3480x7f34c0x7f3500x7f3540x7f3580x7f35c0x7f360

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


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


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


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


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

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


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


Program Behavior

  1. Create an array of random numbers
  2. Print unsorted array
  3. Sort the array
  4. Print sorted array
Arrays in C


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