Data commit

Task/Cumulative-standard-deviation/D/cumulative-standard-deviation.d

@@ -0,0 +1,28 @@
+import std.stdio, std.math;
+
+struct StdDev {
+    real sum = 0.0, sqSum = 0.0;
+    long nvalues;
+
+    void addNumber(in real input) pure nothrow {
+        nvalues++;
+        sum += input;
+        sqSum += input ^^ 2;
+    }
+
+    real getStdDev() const pure nothrow {
+        if (nvalues == 0)
+            return 0.0;
+        immutable real mean = sum / nvalues;
+        return sqrt(sqSum / nvalues - mean ^^ 2);
+    }
+}
+
+void main() {
+    StdDev stdev;
+
+    foreach (el; [2.0, 4, 4, 4, 5, 5, 7, 9]) {
+        stdev.addNumber(el);
+        writefln("%e", stdev.getStdDev());
+    }
+}