'+=' : pointer on left; needs integral value on right

Question

I am confused. I can not use this on a float? must it be a interger ?? I try to define that as a point but I guess I can not convert float to float *

//global definition
float g_posX = 0.0f;

&g_posX -= 3.03f;

Answer 1

If you want to subtract from the float then just name the variable and don't take its address:

g_posX -= 3.03f;

Otherwise, &g_posX is an rvalue that you can't assign to it anything.

Answer 2

You probably simply want to do this:

float g_posX = 0.0f;
g_posX -= 3.03f;

What your code tries to do is take the address of g_posX and subtract 3.03f from the address. That does not work, for two reasons:

• The address is not an lvalue: it cannot be assigned to. Assigning to an address would be meaningless. What would it do, move the variable around in memory?
• Pointer arithmetic can only be done using integers. Fractional addresses do not exist.

Answer 3

well, &g_posX is a pointer to the float. Pointers are memory addresses and (more or less) intereger. To increase the float, simply remove the &.

Answer 4

You don't need the the & before g_posX, just do the maths like

g_posX -= 3.03f;

Answer 5

increment and decrement operators are only defined for integral data types, not for floating point, double, etc.