1 files changed, 47 insertions, 0 deletions
diff --git a/stddev.cpp b/stddev.cpp
new file mode 100644
index 0000000..c804bf3
--- /dev/null
+++ b/stddev.cpp
@@ -0,0 +1,47 @@
+#include <iostream>
+#include <vector>
+#include <cmath>
+
+using namespace std;
+
+const char *argv0;
+
+void usage(){
+	cerr<<"Usage: "<<argv0<<endl
+	    <<"Prints some statistical information about the data on stdin."<<endl
+	    <<"Data is assumed to be a list of floating-point values."<<endl;
+}
+
+int main(int,char **argv){
+	argv0=argv[0];
+
+	vector<double> data;
+
+	double total=0;
+	while(true){
+		double v;
+		cin>>v;
+		if(!cin)break;
+		data.push_back(v);
+		total+=v;
+	}
+	if(data.size()==0){
+		cerr<<"No data"<<endl;
+		return 0;
+	}
+
+	sort(data.begin(),data.end());
+
+	const double s_mean=total/data.size();
+	const double s_mode=data[data.size()/2];
+
+	total=0;
+	for(double v : data){
+		total+=(v-s_mean)*(v-s_mean);
+	}
+	const double s_stddev=data.size()==1?nan(""):sqrt(total/(data.size()-1));
+
+	cout<<"Mean:   "<<s_mean<<endl
+	    <<"Stddev: "<<s_stddev<<endl
+	    <<"Mode:   "<<s_mode<<endl;
+}