FindMissingNewton, C++ (gcc)

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//g++  7.4.0
//Interpolation: Newton Method
//code is created by Rezaul Hoque on January 13,2021
//please contact at jewelmrh@yahoo.com
// if x advances by equal interval and corresponding x value for the value of y to be interpolated is not one of the class limits of x series then Newton method is used for interpolation
 #include <iostream>
using namespace std;
int factorial(int);
int factorial(int n)
{
if(n<0) return 0;
int f=1;
while (n>1)
f *= n--;
return f;
}
int main()
{
int n=5;
float x[n]={15,25,35,45,55};
float y[n]={11.5,12.6,14.3,16.1,18.3};
float * diff1 = new float[n];
float * diff2 = new float[n];
float * diff3 = new float[n];
float ratioX, diff4, corrX,seekY;
//corresponding x value for the value of y to be interpolated 
corrX=17;
ratioX = (corrX-x[0])/(x[1]-x[0]);
 for(int i=0;i<n;i++)
diff1[i] = x[i+1]-x[i];
for(int i=0;i<n;i++)
diff2[i] = diff1[i+1]-diff1[i];
for(int i=0;i<n;i++)
diff3[i] = diff2[i+1]-diff2[i];
diff4= diff3[1]-diff3[0];

//missing Yh
seekY = y[0]+ ratioX*diff1[0]+(ratioX*(ratioX-1)*diff2[0])/factorial(2) +( ratioX*(ratioX-1)*(ratioX-2)*diff3[0])/factorial(3) + ( ratioX*(ratioX-1)*(ratioX-2)*(ratioX-3)*diff4)/factorial(4) ;

cout<<"The missing value for y is "<<seekY;
return 0;
}

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Compilation time: 0.42 sec, absolute running time: 0.16 sec, cpu time: 0.01 sec, memory peak: 6 Mb, absolute service time: 0,68 sec