how to use gets function in c++ code?

Question

In the main function of this code in the case 2 of switch case after entering the string program terminates! What is the problem with the code?

/*this code is a implementation of bubble sort algorithm*/

#include <iostream>
#include<conio.h>
#include<stdio.h>
#include<string.h>
#include<dos.h>

using namespace std;
int counter;
template <class T>//template created

class program//class which holds all the sorting functions
{
    public:
        T *v,x;
        int j,k,l,siz,flag;
        time_t t1,t2;
        char c;
    public:
        void sortlist()//fn to sort characters and numbers
        {
            cout<<endl<<"------->>INTERMEDIATE STEPS<<-------";
            for(k=1;k<=siz-1;k++)//sorting using a bubble sort
            {   flag=0;
                cout<<endl<<"PASS : "<<k<<endl;
                j=0;
                while(j<=siz-1-k)
                {
                    if(v[j]>v[j+1])//comparing two consecutive elements
                    {
                        x=v[j+1];
                        v[j+1]=v[j];
                        v[j]=x;
                        flag++;
                    }
                    for(l=0;l<siz;l++)
                    {
                        cout<<v[l]<<"  ";
                    }
                    cout<<endl;
                    j++;
                }
                cout<<"COMPARISONS:"<<(siz-k)<<endl;
                if(flag==0)
                {
                    cout<<endl<<"----->NO need to carry out more passes"<<endl<<"List is already sorted"<<endl;
                    break;
                }
            }
            }


        void stringsort()//fn to sort the strings
        {

            T a[90][20],b[1][20];
            cout<<"enter the size of list:";
            cin>>siz;
            cout<<"enter the list:";
            cin.ignore();
            for(j=0;j<siz;j++)
            {
                gets(a[j]);
            }
            cout<<endl<<"------->>INTERMEDIATE STEPS<<-------";
            for(k=1;k<=siz-1;k++)//sorting using bubble sort
            {
                flag=0;
                cout<<endl<<"PASS : "<<k<<endl;
                j=0;
                while(j<siz-k)
                {
                    x=strcmp(a[j],a[j+1]);//comparing two consecutive string
                    if(x>0)
                    {
                        strcpy(b[1],a[j+1]);
                        strcpy(a[j+1],a[j]);
                        strcpy(a[j],b[1]);
                        flag++;
                    }
                     for(l=0;l<siz;l++)
                {
                    cout<<a[l]<<"       ";
                }
                cout<<endl;
                    j++;
                }
                cout<<endl<<"COMPARISON:"<<(siz-k)<<endl;
                if(flag==0)
                {
                    cout<<endl<<"No need to carry out more passes"<<endl<<"List is already Sorted"<<endl;
                    break;
                }
            }
            cout<<"SORTED LIST:"<<endl;
            for(j=0;j<siz;j++)
            {
                cout<<endl<<a[j]<<endl;
            }
        }
};
int main()//main fn
{
    int x;
    char c;
    do
    {
        program <char> p1;
        program <int> p2;
        cout<<endl<<"To sort a list of NUMBERS enter -> 1"<<endl<<endl<<"To sort string of CHARACTERS enter -> 2"<<endl<<endl<<"To sort a list OF STRINGS and DOUBLE_STRINGS enter -> 3";
        cout<<endl<<endl<<"Enter either 1 OR 2 OR 3:";
        cin>>x;
        switch(x)
        {
       case 1://to sort list of numbers
            {
                cout<<endl<<"enter the size of list: ";
                cin>>p2.siz;
                cout<<"enter the list: "<<endl;
                p2.v=new int[p2.siz];
                for(p2.l=0;p2.l<=p2.siz-1;p2.l++)
                {
                    cin>>p2.v[p2.l];
                }
                    p2.sortlist();//sort and search in numbers
                cout<<endl<<"SORTED LIST:"<<endl;//sorted list after the bubble sort
                for(x=0;x<=(p2.siz)-1;x++)
                {
                    cout<<p2.v[x]<<endl;
                }
            }
            break;
        case 2://to sort string of character
            {
                    cout<<"enter the string of characters:";
                    cin.ignore()
                    gets(p1.v);
                    p1.siz=strlen(p1.v);
                    p1.sortlist();//sort in characters
                    cout<<endl<<"SORTED STRING:"<<p1.v;
            }
            break;
                case 3://to sort list of strings
                {
                        p1.stringsort();//sort list of string
                }
                break;
            default:
            cout<<"INVALID_CHOICE"<<endl<<endl;
        }
        cout<<endl<<"do u want to enter another list?y/n";
        cin>>c;
    }
    while(c=='y');
        return 0;
}

Answer 1

gets requires that you pass a pointer to enough storage space to hold the string that gets read. Your program passes an uninitialized pointer.

You're not really allowed to do anything with uninitialized values, so in theory your program can crash before it even enters the gets function.

Since the user can pass any amount of data to gets and your program would be responsible for storing it, the function is deprecated. It doesn't even exist any more in the C++ standard library as std::gets since 2011, although ::gets will probably always be available in POSIX. The short answer is, "don't."

You might consider std::string and std::getline instead.