Basics of Arrays: C Program

Lets look at basics of arrays in C programming language. We’ve already covered a lot of stuffs about arrays in Introduction To Arrays: C Programming Language. In this video tutorial we’ll look at some specific things about arrays which we use often.

Related Read:
For Loop In C Programming Language
Sizeof Operator in C Programming Language

Declaring Array Variable

Syntax:

Data_type variable_name[array_size];

Ex: int a[5];

Here array variable is a, it can hold upto 5 integer values.

Index of array starts from zero, and it ends at N-1. N being the size of the array.

For Ex:
int a[N];
Here the first element of array a is at a[0] and the last element is at a[N-1].

Definition of Array

An array is a collection of data items, of same data type, accessed using a common name.

Video Tutorial: Basics of Arrays: C Program

Source Code: Basics of Arrays: C Program

Printing all the elements of an array

#include<stdio.h>

int main()
{
    int a[5] = {1, 2, 3, 4, 5}, i;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Array elements are:
1
2
3
4
5

This prints all the elements of an array. In this program we’re declaring and initializing array variable simultaneously.

Empty curly braces for Array Variable

#include<stdio.h>

int main()
{
    int a[5] = {}, i;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Array elements are:
0
0
0
0
0

Compiler will insert zero in all the empty spots.

Un-initialized Array Variable

#include<stdio.h>

int main()
{
    int a[5], i;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Array elements are:
6356864
4200750
4200656
46
8

If array variable is left un-initialized it’ll have garbage values inside it.

Array Variable Not fully initialized Manually

#include<stdio.h>

int main()
{
    int a[5] = {3, 2}, i;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Array elements are:
3
2
0
0
0

Whenever we assign less values than the array size, the remaining elements will get assigned to 0.

Expression As Array Size

#include<stdio.h>

int main()
{
    int a[2+3] = {3, 2, 1, 0, 5}, i;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Array elements are:
3
2
1
0
5

Any valid expression which ultimately resolves to a positive integer is valid inside square brackets.

Negative Integer Number As Array Size

#include<stdio.h>

int main()
{
    int a[-5] = {3, 2, 1, 0, 5}, i;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
error: size of array ‘a’ is negative
warning: excess elements in array initializer

You can only have positive integer as size of an array and nothing else.

Trying To Assign More Values Than The Array Size

#include<stdio.h>

int main()
{
    int a[5] = {1, 2, 3, 4, 5, 6, 7}, i;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
warning: excess elements in array initializer

You can’t assign more values than the array size.

Overwrite values present at an index: Array

#include<stdio.h>

int main()
{
    int a[5] = {1, 2, 3, 4, 5}, i;

    a[3]  = 100;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Array elements are:
1
2
3
100
5

Here the previous value present at index 3(which can be access using a[3]), is overwritten by value 100.

Garbage Values In Empty Spots: Array

#include<stdio.h>

int main()
{
    int a[5], i;

    a[3]  = 100;

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Array elements are:
6356864
4200766
4200672
100
8

As you can see, the element at index 3 has 100, and all other elements value is just garbage values.

Array Size In Memory

#include<stdio.h>

int main()
{
    int    a[5];
    float  b[5];
    char   c[5];
    double d[5];

    printf("Int    Array: %d\n", 5 * sizeof(int));
    printf("Float  Array: %d\n", 5 * sizeof(float));
    printf("Char   Array: %d\n", 5 * sizeof(char));
    printf("Double Array: %d\n", 5 * sizeof(double));

    return 0;
}

Output:
Int Array: 20
Float Array: 20
Char Array: 5
Double Array: 40

Each cell in array occupies memory space depending upon its data type. Int and float occupies 4 bytes. Char occupies 1 byte. Double occupies 8 bytes. Also remember, size of data type is machine dependent.

Initializing and Accessing Array Elements

#include<stdio.h>

int main()
{
    int a[5], i;

    printf("Enter 5 integer numbers\n");
    for(i = 0; i < 5; i++)
        scanf("%d", &a[i]);

    printf("Array elements are: \n");
    for(i = 0; i < 5; i++)
        printf("%d\n", a[i]);

    return 0;
}

Output:
Enter 5 integer numbers
1
2
3
4
5
Array elements are:
1
2
3
4
5

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