Data Structures Part 1

What is the difference between char *a and char a[]? 

         

There is a lot of difference! char a[] = "string"; char *a = "string"; The declaration char a[] asks for space for 7 characters and see that its known by the name "a". In contrast, the declaration char *a, asks for a  place that holds a pointer, to be known by the name "a". This pointer "a" can point anywhere. In this case its pointing to an anonymous  array of 7 characters, which does have any name in particular.  Its just present in memory with a pointer keeping track of its location. char a[] = "string"; +----+----+----+----+----+----+------+ a: | s | t | r | i | n | g | '\0' | +----+----+----+----+----+----+------+ a[0] a[1] a[2] a[3] a[4] a[5] a[6] char *a = "string"; +-----+ +---+---+---+---+---+---+------+ | a: | *======> | s | t | r | i | n | g | '\0' | +-----+ +---+---+---+---+---+---+------+ Pointer Anonymous array It is curcial to know that a[3] generates different code depending  on whether a is an array or a pointer. When the compiler sees the  expression a[3] and if a is an array, it starts at the location "a",  goes three elements past it, and returns the character there. When it sees the expression a[3] and if a is a pointer, it starts at the location "a", gets the pointer value there, adds 3 to the pointer value,  and gets the character pointed to by that value. If a is an array, a[3] is three places past a. If a is a pointer,  then a[3] is three places past the memory location pointed to by a. In the example above, both a[3] and a[3] return the same character,  but the way they do it is different! Doing something like this would be illegal. char *p = "hello, world!"; p[0] = 'H';