Disp

float sum1 = 0, sum2 = 0;

for (int i = 1; i < n; ++i)
{
	sum1 += x[i] * x[i];
	sum2 += x[i];
}

sum1 /= n;
sum2 /= n;

sum2 *= sum2;

float disp = sum1 - sum2;