Can someone explain how to append an element to an array in C programming?

Question

If I want to append a number to an array initialized to int, how can I do that?

int arr[10] = {0, 5, 3, 64};
arr[] += 5; //Is this it?, it's not working for me...

I want {0,5, 3, 64, 5} in the end.

I'm used to Python, and in Python there is a function called list.append that appends an element to the list automatically for you. Does such function exist in C?

Answer 1

If you want a method that always works, then store the initial size of the array in an int size = 0; variable and increase it every time you append a new element: array[size++] = ...

int array[5];
int size = 0; // you can set the size variable larger 
              // if there are already elements in the array

array[size++] = 12;   // append 1. element
array[size++] = 23;   // append 2. element
array[size++] = 34;   // append 3. element
                      // ...

Answer 2

For some people which might still see this question, there is another way on how to append another array element(s) in C. You can refer to this blog which shows a C code on how to append another element in your array.

But you can also use memcpy() function, to append element(s) of another array. You can use memcpy()like this:

#include <stdio.h>
#include <string.h>

int main(void)
{

int first_array[10] = {45, 2, 48, 3, 6};
int scnd_array[] = {8, 14, 69, 23, 5};
int i;

// 5 is the number of the elements which are going to be appended
memcpy(first_array + 5, scnd_array, 5 * sizeof(int));

// loop through and print all the array
for (i = 0; i < 10; i++) {
    printf("%d\n", a[i]);
  }

}

Answer 3

void Append(int arr[],int n,int ele){
    int size = n+1; // increasing the size
    int arrnew[size]; // Creating the new array:

    for(int i = 0; i<size;i++){
        arrnew[i] = arr[i]; // copy the element old array to new array:

    }
    arrnew[n] = ele; // Appending the element:
}


by above simple method you can append the value 

Answer 4

There are only two ways to put a value into an array, and one is just syntactic sugar for the other:

a[i] = v;
*(a+i) = v;

Thus, to put something as the element at index 4, you don't have any choice but arr[4] = 5.

Answer 5

Short answer is: You don't have any choice other than:

arr[4] = 5;

Answer 6

int arr[10] = {0, 5, 3, 64};
arr[4] = 5;

EDIT: So I was asked to explain what's happening when you do:

int arr[10] = {0, 5, 3, 64};

you create an array with 10 elements and you allocate values for the first 4 elements of the array.

Also keep in mind that arr starts at index arr[0] and ends at index arr[9] - 10 elements

arr[0] has value 0;
arr[1] has value 5;
arr[2] has value 3;
arr[3] has value 64;

after that the array contains garbage values / zeroes because you didn't allocated any other values

But you could still allocate 6 more values so when you do

arr[4] = 5;

you allocate the value 5 to the fifth element of the array.

You could do this until you allocate values for the last index of the arr that is arr[9];

Sorry if my explanation is choppy, but I have never been good at explaining things.

Answer 7

If you have a code like int arr[10] = {0, 5, 3, 64}; , and you want to append or add a value to next index, you can simply add it by typing a[5] = 5.

The main advantage of doing it like this is you can add or append a value to an any index not required to be continued one, like if I want to append the value 8 to index 9, I can do it by the above concept prior to filling up before indices. But in python by using list.append() you can do it by continued indices.

Answer 8

You can have a counter (freePosition), which will track the next free place in an array of size n.