I am trying to use the vector erase function to delete a string that is an element of a vector for a homework assignment. I have tried the line two ways:
vectnames.erase(vectnames[blowup]);
vectnames.erase(blowup);
Does anyone know why the erase function might not be working? As a bit of background, I have to allow the user to enter a planet name to a vector and also let them delete it by name. The example I found online used line #2, but it's not working...
Here is the rest of my code for reference.
#include <iostream>
#include <string>
#include <cmath>
#include <vector>
using namespace std;
class planet
{
private:
string n;
double d, m;
public:
void Density (double d, double m)
{
double Den = m/((4.0/3.0)*M_PI*pow((d/2.0), 3.0));
cout<<"Density: "<<Den<<endl;
}
void SurfaceArea(double d)
{
double S = 4.0*M_PI*pow((d/2.0), 2.0);
cout<<"Surface Area: "<<S<<endl;
}
void Name (string n)
{
string N = n;
cout<<"Name: "<<N<<endl;
}
void Gravity (double G, double m, double d)
{
double F = G*m/pow((d/2.0), 2.0);
cout<<"Force of gravity: "<<F<<endl;
}
};
int main()
{
const double G=6.67384e-11;
int c=0;
string n, N, blowup;
double d=0.0, m=0.0, Den=0.0, S=0.0, F=0.0;
vector<string> vectnames;
vector<double> vectdiam;
vector<double> vectmass;
do
{
cout<<"1. Add a planet\n";
cout<<"2. Delete planet\n";
cout<<"3. Find planet (by name)\n";
cout<<"4. List all planets\n";
cout<<"5. Sort (alphabetical order)\n";
cout<<"6. Quit\n";
cout<<endl;
cout<<"Please select an option from the menu above."<<endl;
cin>>c;
cout<<endl;
if(c==1)
{
planet red;
cout<<"Enter the planet's name: ";
cin>>n;
cout<<"Enter the planet's diameter: ";
cin>>d;
cout<<"Enter the planet's mass: ";
cin>>m;
cout<<endl;
vectnames.push_back(n);
vectdiam.push_back(d);
vectmass.push_back(m);
red.Name(n);
red.Density(d, m);
red.SurfaceArea(d/2.0);
red.Gravity(G, m, d);
cout<<endl;
}
else if (c==2)
{
cout<<"Fire the Death Star's superlaser at: "<<endl;
cin>>blowup;
vectnames.erase(vectnames[blowup]); //This is the part that I'm having trouble with
for (int i=0; i<vectnames.size(); i++)
{
cout<<vectnames[i]<<endl;
}
}
else if (c==4)
{
for (int i=0; i<vectnames.size(); i++)
{
planet red;
cout<<"Planet name: "<<vectnames[i]<<endl;
cout<<"Planet diameter: "<<vectdiam[i]<<endl;
cout<<"Planet mass: "<<vectmass[i]<<endl;
red.Density(vectdiam[i], vectmass[i]);
red.SurfaceArea(vectdiam[i]/2.0);
red.Gravity(G, vectmass[i], vectdiam[i]);
cout<<"************************"<<endl;
cout<<endl;
}
}
} while (c!=6);
system("pause");
return 0;
}
I'm going to work with vector<planet> planets; because it's got a nice ring to it and it's purpose is about as close to obvious as I can get without using an idiotically long name like VectorOfPlanets.
In order to erase an item from a vector you have to know where it is. There are a bunch of ways to do this from brute force searching the vector in a loop until you find the index of the item you want and then calling planets.erase(planets.begin + index);
I thought there was a overload of std::find you could pass a comparator function, but it looks like I'm on crack. Glad I didn't make an ass of myself by suggesting it. Wait... Am I writing out loud? Crap. Hate it when I do that.
Read up on how to create an operator= method in the planet class and you can use std::find. With it you can:
vector<planet> planets;
vector<planet>::iterator it;
it = std::find(planets.begin(), planets.end());
if (it != planets.end())
{
planets.erase(it);
}