Calculating Standard Deviation & Variance in C++

As the other answer by horseshoe correctly suggests, you will have to use a loop to calculate variance otherwise the statement

var = ((Array[n] – mean) * (Array[n] – mean)) / numPoints;

will just consider a single element from the array.

Just improved horseshoe’s suggested code:

var = 0;
for( n = 0; n < numPoints; n++ )
{
  var += (Array[n] - mean) * (Array[n] - mean);
}
var /= numPoints;
sd = sqrt(var);

Your sum works fine even without using loop because you are using accumulate function which already has a loop inside it, but which is not evident in the code, take a look at the equivalent behavior of accumulate for a clear understanding of what it is doing.

Note: X ?= Y is short for X = X ? Y where ? can be any operator. Also you can use pow(Array[n] - mean, 2) to take the square instead of multiplying it by itself making it more tidy.

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