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Is there any way by which I can initialize all the elements of an array(already declared) in one statement?? That is, without using loops

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Short answer: in C “initialization” is the compile-time/declaration action and you cannot use an initializer on an already-declared array — later changes are assignments to elements. That is the distinction was getting at (and what confused and ). (stackoverflow.com)

Why you can’t write a single = for an array: objects of array type are non‑modifiable lvalues, so the language forbids whole-array assignment (you must assign elements, copy memory, or assign a containing struct). That is why people recommend loops, memcpy, or other tricks instead of a = b;. (cppreference.net)

Practical one-statement patterns for an already-declared array:

  • Zero the storage in one call (common idiom): use memset(arr, 0, sizeof arr);. This is widely used, but note the portability caveat — filling with all‑zero bits is not guaranteed by the standard to produce a null pointer or a floating‑point +0.0 on every implementation. Use explicit element assignment if you need strict portability for pointers/floats. (stackoverflow.com)

  • Copy a literal initializer in one call (C99+): create a compound literal and memcpy it into the existing array. This is a concise way to “assign” a full set of values in one statement without writing an element loop:

/* C99 or later */
memcpy(dst, (int[]){ 1, 2, 3, 4, 5 }, sizeof dst);

Compound literals create a temporary object which memcpy copies into dst. (landley.net)

If elements must be computed or types are not POD‑like, a simple for loop or a small helper function is the clearest, most portable solution — it’s what compilers optimize most reliably. This complements 's note about declaration-time zeroing and 's point about omitted elements being zero-initialized at definition. (landley.net)

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Member Avatar for Banfa

You can't initialise anything that has already been declared. You can only initialise something at the time it is created, after that it becomes assignment.

And to answer the spirit of your question no there is no way to assign to all members of an existing array without recourse to a for loop (with the exception of using memset on an array of char).

Member Avatar for anirudh33

hey there,
And if you want to ask is if we can initialize at the time of declaration we do it like this,

int a[10]={1,2,3,4,5};

To assign a value later to any element of the array code will be,

a[1]=33;
a[4]=55;

Anirudh

Edited by anirudh33 because: n/a
Member Avatar for .It.

If you want to initialize all the elements of an array to 0, you can use this

#define SIZE 5
int my_array[SIZE] = {0};

Check out memset and memcpy also.

Member Avatar for WaltP

You can't initialise anything that has already been declared. You can only initialise something at the time it is created, after that it becomes assignment.

Not true. By setting a value, (for example- a loop counter before a while loop) is initializing the value.

Edited by WaltP because: n/a
Member Avatar for Dexxta27

Not true. By setting a value, (for example- a loop counter before a while loop) is initializing the value.

When you do that, aren't you declaring that variable?? That makes the guy you quoted correct.

Member Avatar for WaltP

I guess the terminology has changed, then. For the past 35 years initializing a variable has been setting it to a know value just before entering a piece of code (like a loop) that does some kind of processing. When did that change?

What you call initializing I always called defining.

Edited by WaltP because: n/a
Member Avatar for Dexxta27

I've been learning just about 1-2 years now, but initializing has always been basically assigning a value when the variable, or whatever it is, is being declared.

I've don't know how you put a counter before a while loop. I know about IN the for loop though, so I guess we are WAY different

Member Avatar for chaitanya88

I think The initializer for an array is a comma-separated list of constant expressions enclosed in braces ({ }). The initializer is preceded by an equal sign (=). You do not need to initialize all elements in an array. If an array is partially initialized, elements that are not initialized receive the value 0 of the appropriate type.


for eg:
Element Value Element Value
matrix[0][0] 1 matrix[1][2] 0
matrix[0][1] 2 matrix[1][3] 0
matrix[0][2] 0 matrix[2][0] 5
matrix[0][3] 0 matrix[2][1] 6
matrix[1][0] 3 matrix[2][2] 0
matrix[1][1] 4 matrix[2][3] 0


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Member Avatar for benwilliams

We have to used
Syntax data type array[]

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