Programacion

# include <iostream>
# include <cmath>
# include <cstdlib>
# include <string>
using namespace std;

int main (){

int a, b, c, opc, artriangulo, arcuadrado,arrectangulo;
double radio, pi, arcirculo;
char R;
for(;;){
system("cls");
cout<<"\t\t*****************************************************\n";
cout<<"\t\t*********U.P.N.F.M ***********\n";
cout<<"\t\t********* PREUFOD SEDE LA CEIBA ***********\n";
cout<<"\t\t********* PROYECTO DE PROGRAMACION ***********\n";cout<<"\t\t********* GRUPO NUMERO 3 ***********\n";
cout<<"\t\t********* Edgardo & Paola ***********\n";cout<<"\t\t*****************************************************\n";
cout<<"\t\t*****************************************************\n";
cout<<"\t\t*****************************************************\n";cout<<"\t\t********* QUE DESEA CALCULAR? ***********\n";
cout<<"\t\t********* AREA DEL TRIANGULO:1 ***********\n";
cout<<"\t\t********* AREA DEL CUADRADO:2***********\n";
cout<<"\t\t********* AREA DEL RECTANGULO:3 ***********\n";
cout<<"\t\t********* AREA DEL CIRCULO :4 ***********\n";
cout<<"\t\t********* SALIR DELA APLICACION:5 ***********\n";
cout<<"\t\t*****************************************************\n";

cout<<"INTRODUZCA LA OPCION QUE DESEA EJECUTAR\n";
cin>>opc;if(opc<1){
system("cls");
cout<<endl<<"ERROR!!!! NUMERO INGRESADO INVALIDO"<<endl<<endl;
system("pause");
continue;
}if (opc>5){
system("cls");
cout<<endl<<"ERROR!!!! NUMERO INGRESADO INVALIDO"<<endl<<endl;
system("pause");...