Why array assignment operation doesn't exist but structure assignment does in C language?

Question

int a[10];
int b[10];

a = b; // illegal

typedef struct {
    int real;
    int imag;
    } complex;

complex c,d;
c = d; //legal

[I realize that

Answer 1

An array name is a const pointer so you can't change what it is pointing to.

Assuming that you meant c = d on the last line is legal, it's simply copying a non-const variable to another non-const variable, which is perfectly legal.