What is causing this Point-to-Object Error in C?

Question

So I have defined

#define SYS_LEN 50.0
#define N_CELLS ((int)SYS_LEN)

as well as

extern double *array_one

which I populate via

array_one[0] = 0.5*SYS_LEN
array_one[1] = 0.25*SYS_LEN

I then go onto define function

void function(void)
{
int is, ix;
double X;
for (is = 0; is < MAX_VALUE; is++){
    for (ix = 0; ix < MAX_VALUE_TWO; ix++)
    {
    X[is] = 0.5 + (double)ix - array_one[is]
    }
}}

However I get an error stating 'expression must have pointer-to-object type'. Not too sure why this is, any help would be appreciated

Thank you

Answer 1

There are potentially multiple problems.

Potential problem one is you say you allocated memory for

extern double *array_one

and assigned two values. But did you declare enough memory for array_one, and initialize with values, to account for the maximum loop index in your function, which is MAX_VALUE ? If not you would get an access violation if you didn't assign enough memory.

Problem two is definite - it is that you declared a double scalar with double X, but attempted to access it as though you had declared an array.

Assuming you had defined MAX_VALUE as an integer > 1, the solution would be to declare an array of doubles for X:

For example if you had somewhere done

#define MAX_VALUE 20

the corresponding code would need to be

void function(void)
{
int is, ix;
double X[MAX_VALUE];
for (is = 0; is < MAX_VALUE; is++){
    for (ix = 0; ix < MAX_VALUE_TWO; ix++)
    {
    X[is] = 0.5 + (double)ix - array_one[is];
    }
 }
}