Why we generally not make a variable size array.

Question

If we have to make a 'n' size array then we generally write like arr[100] "n<100" and using loop we enter n variable.Instead of making 100 size array why we not make n size array.

Answer 1

You can create arrays of non-const size

Please, consider the following code:

#include <stdio.h>

int main()
{
    int length;
    printf("How many element would you like to store in the array?\nElement count: ");
    scanf("%d", &length);

    int array[length];
    printf("\nArray declaration of length %d is done...\n", length);
    for (int i = 0; i < length; i++)
        array[i] = i;

    printf("Array is now filled with values...\n");

    return 0;
}

If you run this piece of code, you can see that we can indeed allocate and use an array whose length and size was not known at compile time.

If I recall correctly, in some old version of C this was not supported, hence the restrictions you've seen. The alternative was to allocate/deallocate memory for such arrays (malloc/free). But this is not needed for two decades now or so, unless you force the compiler to use some very old (20+ years) standards.