simple Low pass filter code

Hi, This is a simple low pass filter code, i am not sure how well it works, it seems really depends on value of first input in the input array input[0]. and value of u. i am not sure what is the best value for the constant in u = t / (t +constant); and also do you have any recommandation to improve it. Thanks.

#include <iostream>
#include<math.h>
using namespace std;

int main()
{
double t=10;
double u=0;
u = t / (t +constant);

double input[10]={1, 1.05, 1.11, 1.2, 1, 1.21, 1.01, 1.02, 1, 1.44};
double output[10]={0 ,0, 0 ,0 ,0, 0, 0, 0, 0, 0 };
double o;
o=(1.2+1.05+1.11+1.2+ 1+1.21+1.01+1.02+ 1+ 1.44)/10;
output[0] = input[0];
cout<<u <<endl;
for(int i=1;i<10;i++)
{

output =u*(input - output[i-1]) + output[i-1];
cout<<i<<" i "<<output<<endl;

}
cout<<output[9]<<endl;
cout<<o<<endl;


return 0;
}