Initialize a variable sized array

Question

I have an array in C described like:

int N; /*size of array*/
scanf("%d",&N);
int A[N];

How do I initialize all it's elements to same element like 5. Without using loop.
Need a very efficient method.

Answer 1

If the initial value was 0, you could use the memset function: http://www.cplusplus.com/reference/cstring/memset/
memset would be a complete solution if the size of your data type was 1 byte such as with a char array.

Your question mentions 5 and your data type of int usually occupies 4 bytes so memset won't work. You could set an int value of something like 0x05050505 using memset only because that's a repeating byte value. 0 works for the same reason since 0 is stored as 0x00000000 which is repeated bytes in a 32-bit int.

If you don't consider recursion to be a loop, you could do something like:
#include <stdio.h> // defines scanf
#include <stdlib.h> // defines malloc

void fillArray(int initialValue, int *A, int N) {
if (N <= 0)
return; // nothing to do so end recursion.
A[0] = initialValue;
fillArray(initialValue, A + 1, N - 1); // Fill the rest.
}

int main() {
int N;
int * A;
scanf("%d",&N);
A = (int *)malloc(sizeof(int) * N);
// Now A has N elements. They have unpredictable values, though.
fillArray(5, A, N);
// Now A[0] is 5, A[1] is 5...

return 0;
}

A related question is at: https://stackoverflow.com/questions/2891191/how-to-initialize-an-array-to-something-in-c-without-a-loop but it discusses an array with a length that is known at compile time. A user-defined array length is more difficult to initialize without a loop.

Answer 2

Anvay The first&second is used only with GCC compilers.
https://code.sololearn.com/cNeBoPeDi248/?ref=app
note that this is not a user-defined array length v