static « size « C Array Q&A

1. How to change a 2d array from dynamic to static of a specific size?    stackoverflow.com

I currently have the dynamic array:

char *myData[500][10]; //myData is the name of an array of[500][10] pointers to type char.

2. Casting a 'BigStruct' to a 'SmallStruct' in C (similar structs with static arrays of different sizes)    stackoverflow.com

Supposed that for some reason you are only allowed to use static memory in a C program. I have a basic structure that I am using in several places defined as below:

#define ...

3. static char arrays size    bytes.com

Hello , I always had the feeling that is better to have char arrays with the size equal to a power of two. For example: char a_str[128]; // feels ok char b_str[100]; //feels not ok. Is that true , and if is true then what is the reason behind this? ( I suppose that is something related to memory alignment but ...