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

int main(int argc, char *argv[])
{
    int n;
    float E,Re,d,f,ED,ln,y,yRe,Ref,xRe,A,B,AB,ab,x,h,z, M,Vo,D,p,p2,E3,xE2,P,Vo2;
    float friccion1;
    float friccion2;
    float friccion3;

    cout<<"Ingrese el numero de ecuacion: \n\n1. Ecuacion de Pavlov\n2. Ecuacion de Colebrook\n3. Ecuacion de Churchill\n4. Ecuacion de Blake Kozeni\n5. Ecuacion de Burke Plummer\n\n";
    cin>>n;

    system("CLS");

    switch (n)
    {
           case 1: {cout<<"Ingrese la variable E"<<endl;
                  cin>>E;
                  cout<<"Ingrese la variable d"<<endl;
                  cin>>d;
                  cout<<"Ingrese la variable Re"<<endl;
                  cin>>Re;
                  xRe = (6.81/Re);
                  friccion1 = ((1/3.7)*(E/d)) + pow(static_cast<double>(xRe),0.9);
                  friccion2 = (-4)*(log(resultado1)/log(10));
                  cout<<"El resultado es "<friccion2<<endl;
                  }
                  break;
           case 2: {
                cout<<"Ingrese la variable E"<<endl;
                  cin>>E;
                  cout<<"Ingrese la variable d"<<endl;
                  cin>>d;
                  cout<<"Ingrese la variable Re"<<endl;
                  cin>>Re;
                  cout<<"Ingrese la variable f"<<endl;
                  cin>>f;
                  Ref = (Re/(sqrt(f)));
                  friccion1 = ((1/3.7)*(E/d)) + (1.255/Ref);
                  friccion2 = (-4)*(log(resultado1)/log(10));
                  cout<<"Factor de friccion: "<<friccion2<<endl;
                  }
                  break;
           case 3: {
                cout<<"Ingrese la variable E"<<endl;
                  cin>>E;
                  cout<<"Ingrese la variable D"<<endl;
                  cin>>d;
                  cout<<"Ingrese la variable Re"<<endl;
                  cin>>Re;
                  {
                          xRe = pow(7/Re,0.9);
                          ED = (0.27*(E/d));
                          x = (1/(xRe+ED));
                          ln = 2.457*(log(x));
                          A = pow(ln,16);
                  }
                  {
                          y =(37.530/Re);
                          B = pow(y,16);
                  }
                  yRe = pow(8/Re,12);
                  h = pow(A+B,3);
                  AB = sqrt(h);
                  ab = 1/AB;
                  z = 2*(yRe + ab);
                  resultado1 = pow(z,1.0/12);
                  cout<<"Factor de friccion "<<friccion1<<endl;
                   }
                   break;
           case 4: {
                cout<<"Ingrese la variable M"<<endl;
                  cin>>M;
                  cout<<"Ingrese la variable Vo"<<endl;
                  cin>>Vo;
                  cout<<"Ingrese la variable D"<<endl;
                  cin>>D;
                  cout<<"Ingrese la variable p"<<endl;
                  cin>>p;
                  cout<<"Ingrese la variable E"<<endl;
                  cin>>E;
                  p2 = pow(p,2);
                  xE2 = pow((1-E),2);
                  E3 = pow(E,3);
                  resultado1 = 150*((M*Vo)/(D*p2))*(xE2/E3);
                  cout<<"El resultado es "<<friccion1<<endl;
                   }
                   break;
           case 5: {
                cout<<"Ingrese la variable P"<<endl;
                  cin>>P;
                  cout<<"Ingrese la variable Vo"<<endl;
                  cin>>Vo;
                  cout<<"Ingrese la variable D"<<endl;
                  cin>>D;
                  cout<<"Ingrese la variable p"<<endl;
                  cin>>p;
                  cout<<"Ingrese la variable E"<<endl;
                  cin>>E;
                  Vo2 = pow(Vo,2);
                  E3 = pow(E,3);
                  friccion1 = 1.75*((P*Vo2)/(D*p))*((1-E)/E3);
                  cout<<"El resultado es "<<friccion1<<endl;
                   }
    }

    system("PAUSE");
    return;
}

In function 'int main(int, char**)':
Line 29: error: 'resultado1' was not declared in this scope
compilation terminated due to -Wfatal-errors.