Pointer for array to calculate average in C++ -

i got question on pointer in c++ :

write function computes average value of array of floating-point data:

double average(double* a, int size)

in function, use pointer variable, not integer index, traverse array elements.

and here solution :

int main() { const int size = 5; double num_array[] = {2,2,3,4,5};  double* = num_array; cout << average(a,size); cout << endl;  system("pause"); return 0; }  double average(double* a,const int size) { double total = 0; (int count =0; count< size; count++){     total = total + *(a + count); } return total/size; } 

it works fine have question on loop on pointer in average function. if replace statement in loop :

    total = total + a*; 

(i thought supposed add number in array unfortunately gives me wrong answer)

so *(a + count) do? if possible, can please brief me on how works?

thanks in advance.

a pointer double.

if write *a, pointer gets dereferenced , data pointer points at, i.e. double value. note asterisk has in front of pointer. (it's "prefix" unary operator.)

a* no valid syntax (it tries multiply a still has follow ...)

a + count pointer arithmetic. gives a count numbers of elements offset original a pointer. points count-th element in array.

*(a + count) dereferences pointer, gives count-th element of array.

a[count] same; it's nicer syntax.

note: can use a++ in loop. increments pointer 1 position in array. next time dereference a using *a, returns next entry. loop can rewritten this:

double total = 0; (int count = 0; count < size; count++){     total = total + *a;    // access element points     a++;                   // move pointer 1 position forward } 

you can combine increment , dereferencing operations 1 expression. postfix-increment syntax a++ return old pointer , increment pointer 1 position. dereferencing a++ means dereference old pointer.

double total = 0; (int count = 0; count < size; count++){     total = total + *(a++); } 

the second note want give you don't need integer variable here count element. since pointer carries information, counter used stop loop. can done comparing pointer "end pointer", keep in variable:

double total = 0; double *end = + size; // store end of array while(a < end) {     total = total + *(a++); } 

as can see, converted for loop while loop since no longer need initialize or increment (remember: going next entry of array done in body!).

i hope illustrates pointer arithmetic little bit. can "calculate" pointers indexing variables (your count variable). can subtract them calculate offsets between pointers, example.