Eulers Method, Eulers Modified and Eulers Improved method implementation in CPP language

/*
    Eulers method implementation in CPP Language-----

    Md. Alamgir Hossain
    Department of Computer Science & Engineering.
    Jessore University of Science & Technology, Bangladesh.
    Email : alamgir.cse14.just@gmail.com
*/

#include<bits/stdc++.h>
using namespace std;

float equation(float x, float y)
{
    ///Here enter the right side of your differential equation---
    ///Some example of equation in the res variable--

    ///You can check with your desired equation
    ///From here remove comment and check for another equation...


    float res;

    ///Equation start
   // res = (3*x*x)+1;
    res = (x*x)+(y*y);
   // res = y+(x*x);
   // res = ((2*y)/x)+(x*x*x);
    //res = y-((2*x)/y);

    return res;

}
///Main function start from here----
int main()
{

    float x0;
    cout<<"Enter the value of X0 : ";
    cin>>x0;

    float y0;
    cout<<"Enter the value of Y0 : ";
    cin>>y0;

    float xn;
    cout<<"Enter the value of Xn or x1 : ";
    cin>>xn;

    char pr;
    cout<<"If you want to enter the value of h press 1 else other : ";
    cin>>pr;
    float x1 = 0.0, h, h2;
    if(pr == '1'){
        cout<<"Enter the value of h : ";
        cin>>h2;
        h = h2;
    }else{
        h = xn - x0;
    }

    float y1,y2;
    x1 = h + x0;
    y1 = y0 + (h * equation(x0, y0));
    y2 = y1 + (h * equation(x1, y1));

    ///Now we want to check Eulers/Eulers Modified/Eulers Improved method--

    cout<<"Press 1 for Eulers method, 2 for Modified and 3 for Improved method--";
    char p;
    cin>>p;

    ///Machanism start for Eulers Method----------

    if(p == '1'){
        cout<<"Press 2 for two values 1 for one values";
        char pp;

        if(pp == '2'){
            cout<<"Enter the second value of x : ";
            float x2;
            cin>>x2;

            cout<<"\nThe Result for Y1("<<xn<<") using Eulers method is : "<<y1<<"\n";
            cout<<"\nThe Result for Y2("<<x2<<") using Eulers method is : "<<y2<<"\n";
        }
        else if(pp == '1'){
            cout<<"\nThe Result for Y1("<<xn<<") using Eulers method is : "<<y1<<"\n";
        }
        else{
            cout<<"Please enter valid value---\n";
            return 0;
        }
    }
    ///Eulers modified method start----------
    else if(p == '2')
    {
        float v,v1,v2,v11,v21,vv;
        v1 = x0 + (h/2);
        v2 = y0 + ((h/2)+equation(x0,y0));
        v = (h*(equation(v1,v2))+y0);


        v11 = x1 + (h/2);
        v21 = v + ((h/2)*equation(x1,v));
        vv = (h * (equation(v11,v21))) + v;

        cout<<"Press 2 for two values 1 for one values";
        char pp;
        cin>>pp;


        if(pp=='2'){
            cout<<"Enter the second value of x : ";
            float x2;
            cin>>x2;

            cout<<"\nThe Result for Y1("<<xn<<") using Eulers modified method is : "<<v<<"\n";
            cout<<"\nThe Result for Y2("<<x2<<") using Eulers modified method is : "<<vv<<"\n";
        }
        else if(pp=='1'){
            cout<<"\nThe Result for Y1("<<xn<<") using Eulers Modified method is : "<<v<<"\n";
        }
        else{
            cout<<"\nPlease enter valid value---\n";
            return 0;
        }

    }
    ///Mechanism for Improved Eulers Method is------
    else if(p == '3'){
        float y1,y2;

        y1 = y0 + (h/2) * ((equation(x0,y0)) + (equation((x0+h),(y0+(h*(equation(x0,y0)))))));
        y2 = y1 + (h/2) * ((equation(x1,y1)) + (equation((x1+h),(y1+(h*(equation(x1,y1)))))));

        cout<<"Press 2 for two values 1 for one values";
        char pp;
        cin>>pp;


        if(pp=='2'){
            cout<<"Enter the second value of x : ";
            float x2;
            cin>>x2;

            cout<<"\nThe Result for Y1("<<xn<<") using Improved Eulers method is : "<<y1<<"\n";
            cout<<"\nThe Result for Y2("<<x2<<") using Improved Eulers method is : "<<y2<<"\n";
        }
        else if(pp=='1'){
            cout<<"\nThe Result for Y1("<<xn<<") using Improved Eulers Modified is : "<<y1<<"\n";
        }
        else{
            cout<<"Please enter valid value---\n";
            return 0;
        }
    }

    cout<<"\n\nThank You!!!!!\n\n";
    return 0;
}


///Input/Output Example-----------------
/*
Enter the value of X0 : 0
Enter the value of Y0 : 1
Enter the value of Xn : .1
If you want to enter the value of h press 1 else other : 1
Enter the value of h : .1
Press 1 for Eulers method, 2 for Modified and 3 for Improved method--2
Press 2 for two values 1 for one values2
Enter the second value of x : .2

The Result for Y1(0.1) using Eulers modified method is : 1.4205

The Result for Y2(0.2) using Eulers modified method is : 1.65437


Thank You!!!!!

*/