number of elements in array in c

How can I find the number of elements in an array?

stackoverflow.com › questions › 10290610 › how-can-i-find-the-number-of-elements-in-an-array

If you have your array in scope you can use sizeof to determine its size in bytes and use the division to calculate the number of elements:

#define NUM_OF_ELEMS 10
int arr[NUM_OF_ELEMS];
size_t NumberOfElements = sizeof(arr)/sizeof(arr[0]);

If you receive an array as a function argument or allocate an array in heap you can not determine its size using the sizeof. You'll have to store/pass the size information somehow to be able to use it:

void DoSomethingWithArray(int* arr, int NumOfElems)
{
    for(int i = 0; i < NumOfElems; ++i) {
        arr[i] = /*...*/
    }
}

Answer from Pavel Zhuravlev on Stack Overflow

Stack Overflow

stackoverflow.com › questions › 10290610 › how-can-i-find-the-number-of-elements-in-an-array

c - How can I find the number of elements in an array? - Stack Overflow

Top answer

1 of 16

If you have your array in scope you can use sizeof to determine its size in bytes and use the division to calculate the number of elements:

#define NUM_OF_ELEMS 10
int arr[NUM_OF_ELEMS];
size_t NumberOfElements = sizeof(arr)/sizeof(arr[0]);

void DoSomethingWithArray(int* arr, int NumOfElems)
{
    for(int i = 0; i < NumOfElems; ++i) {
        arr[i] = /*...*/
    }
}

2 of 16

int a[20];
int length;
length = sizeof(a) / sizeof(int);

and you can use another way to make your code not be hard-coded to int

Say if you have an array array

you just need to:

int len = sizeof(array) / sizeof(array[0]);

reddit.com › r/c_programming › getting the number of element of an array

r/C_Programming on Reddit: Getting the number of element of an array

August 28, 2022 -

hi, I'm new in C. I'm having a hard time finding the number of elements in an int array.
Here's what I'm trying to achieve.
I've defined a macro
#define MAXSZ 30

Then I've declared an array
int arr[MAXSZ];

What I wanted to do, is, taking user input to initialize the array up until the user inputs -1. Then get the number of elements.
int item;
for(int i = 0; i < MAXSZ; i++) {
scanf("%d", &item);
if (item == -1) break;
else arr[i] = item;
}

Now, when I'm trying to get the number of elements.
For input
1
2
3
5
6
-1
It shows 30 elements (as it's supposed to).
Output
30
0x7ffe9be05320 -> 1
0x7ffe9be05324 -> 2
0x7ffe9be05328 -> 3
0x7ffe9be0532c -> 5
0x7ffe9be05330 -> 6
0x7ffe9be05334 -> 32572
0x7ffe9be05338 -> -1293942784
0x7ffe9be0533c -> -182336
0x7ffe9be05340 -> -1381222790
0x7ffe9be05344 -> 32572
0x7ffe9be05348 -> 0
...

My question is, how do I get rid of the garbage values & only get the number of items that has been given as input?

Top answer

1 of 4

You seem to have some misunderstandings of what an array is. The number of elements in the array int arr[MAXSZ] is MAXSZ. The content and meaning of those elements is left to the programmer. So... what's your actual problem here? You can keep count of how many entries you've added within your loop int item; int num_items=0; for(; num_items < MAXSZ; num_items++) { scanf("%d", &item); if (item == -1) break; else arr[num_items] = item; } Or you can fill the array with a "known-bad" value, and then only check elements that aren't that value for(int i = 0; i < MAXSZ; i++) { arr[i] = -99; }

2 of 4

You can memset the array to zero. You can also set each element to zero before the scanf portion in the loop You can allocate a pointer of size 30* int by calling calloc (don’t forget to free before leaving the scope)

Discussions

Count the number of elements in an array in C - Stack Overflow

Not only can arrays be dynamically ... but as of C99 their size can be dynamic as well -- so-called Variable-Length Arrays (VLAs). 2013-04-10T21:57:55.36Z+00:00 ... You are most likely doing this inside the function to which you pass the array. The array decays as pointer to first element So You cannot ... More on stackoverflow.com

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calc. number of elements in array - C++ Forum

However, std::vector should be preferred. It has a size()-function returning the number of elements. As soon as array to pointer decay ocurres (which will happen really fast), your method won't work anymore. ... i tried this, but sizeof(array) always comes out to be 4, being an integer ... More on cplusplus.com

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