lvalue required as increment operand

x++ is the short form of x = x + 1. However, x here is an array and you cannot modify the address of an array. So is the case with your variable y too.

Instead of trying to increment arrays, you can declare an integer i and increment that, then access the i‘th index of an arrays.

char x[10], y[5] = "Hello";
int i = 0;
while (y[i] != 0)
{
    x[i] = *y[i];
    i++;
}
x[i] = 0;