Why would someone take an address, typecast the pointer, and then dereference it?

Question

I ran into a weird code snippet while following an image processing guide. The language is C. What is the purpose of taking an address, casting the pointer, then dereferencing it? I am new to C, so I am unsure if this is a common practice and its purpose.

unsigned char header[];

// not sure why we are dereferencing the array then getting its address and casting it into an int pointer then dereferencing that.
int width = *(int *)&header[18]; 
int height = *(int *)&header[22];
int bitDepth = *(int *)&header[28];

// why not this?
int width = (int) header[18]; 
int height = (int) header[22];
int bitDepth = (int) header[28];

Answer 1

It seems the type of the pointer header is not int *. Maybe it has the type void * or char * or unsigned char *.

So to get an integer you need to cast the pointer to the type int * and then to dereference it to get the value pointed to by the pointer.