How to place one random ship in a gameboard

For a school assignment I have to create a battleship game where one random 4 length battleship (horizontal or vertical) is generated in a 8x8 gameboard. The player has 15 torpedoes to try and sink the ship. I used a 2D vector and have finished most of the code:

#include <iostream>
#include <vector>
#include <stdlib.h>
#include <time.h>

using namespace std;

void generateship(vector<vector<int> >&field);
void fire(vector<vector<int> >&field);
void display(const vector<vector<int> >field);

int main()
{
    srand(time(0));

    vector<vector<int> >field(8);
    for (int x = 0; x < field.size(); x++)
        field[x].resize(8);
    for (int x = 0; x < field.size(); x++)
        for (int y = 0; y < field[y].size(); y++)
            field[x][y] = 0;

    generateship(field);
    fire(field);


    system("pause");

    return 0;
}
void generateship(vector<vector<int> >&field)
{
    int row1 = rand() % 8;
    int col1 = rand() % 8;
    do 
    {
        int row2 = rand() % 3 + (row1 - 1);
        int col2 = rand() % 3 + (col1 - 1);
    } while (row2 != row1 && col2)
    int col3 = rand()
    display(field);
}
void fire(vector<vector<int> >&field)
{
    int row, col;
    int torps = 15;
    int hitcounter = 0;
    while (hitcounter != 4 || torps != 0)
    {
        cout << torps << " torpedoes remain. Fire where? ";
        cin >> row >> col;
        switch (field[row][col])
        {
        case 0: cout << "Miss!" << endl << endl;
            field[row][col] = 2;
            break;
        case 1: cout << "Hit!" << endl << endl;
            field[row][col] = 3;
            hitcounter = hitcounter + 1;
            break;
        case 2: cout << "Missed again!" << endl << endl;
            break;
        case 3: cout << "Hit again!" << endl << endl;
            break;
        }
        torps = torps - 1;
        display(field);
    }
    if (hitcounter == 4)
        cout << "You win!";
    else if (torps == 0)
        cout << "You are out of torpedoes! Game over.";
}
void display(const vector<vector<int> >field)
{
    for (int row = 0; row < 8; row++)
    {
        for (int col = 0; col < 8; col++)
        {
            switch (field[row][col])
            {
            case 0:     cout << ". ";
                break;
            case 1:     cout << ". ";
                break;
            case 2:     cout << "X ";
                break;
            case 3:     cout << "O ";
                break;
            }
        }
        cout << endl;
    }
}

As you can probably see I am struggling with the "generateship" function. My goal is to generate RANDOMLY one 4x1 ship (horizontal or vertical) that is completely within my 8x8 2D vector. Any advice/help/comments appreciated!