Numerical Mathematics : Secant Method code

Sample equation for Secant Method

where X-1=3

and x0=4 ;

F(x)=2x³-11.7x²+17.7x¹-5

 //scant method  
 #include<stdio.h>  
 #include<math.h>  
 #include<iostream>  
 using namespace std;  
 int main()  
 {  
   float xi,Xii,newxi,Es,a[40],old=0,Ea;  
   int n,K;  
   cout<< "HIghest power in the equation : " ;  
   cin>>n;  
   //.........................................  
   printf("Enter Xi =");  
   scanf("%f",&xi);  
   printf("Enter Xii =");  
   scanf("%f",&Xii);  
   printf("Enter Es =");  
   scanf("%f",&Es);  
   //..........................................  
   printf("\n");  
   printf("enter coefficient :\n");  
   for (int i=n; i>=0; i--)  
   {  
     printf("X^%d =",i);  
     scanf("%f",&a[i]);  
   }  
   //...........................................  
   while(1)  
   {  
     float fxi=0,fXii=0;  
 //  
     for (int i=n; i>=0; i--)  
     {  
        fxi=fxi+a[i]*pow(xi,i);  
        fXii=fXii+a[i]*pow(Xii,i);  
     }  
     newxi=xi-((fxi*(Xii-xi))/(fXii-fxi));  
 //  printf("\n\n\nSTEP no: %d\n",K+1);  
     printf("\nXi  = %.2f",xi);  
     printf("\nfxi = %.2f",fxi);  
 //  
     printf("\nXii  = %.2f",Xii);  
     printf("\nfXii = %.2f",fXii);  
 //  
     printf("\nnew Xi  = %.2f",newxi);  
 //  
     Ea=((newxi-old)/newxi)*100;  
     old =newxi;  
     //cout <<" now =" <<old;  
     if(Ea<0)  
     {  
       Ea=Ea*(-1);  
     }  
     printf("\nEa= %f\n",Ea);  
     if(Ea<Es)  
     {  
       break;  
     }  
     Xii=xi;  
     xi=newxi;  
     K++;  
   }  
   return 0;  
 }