for loop's init-statement with two types of variable

Question

I want to declare two types of variables in for's init-statement. like the following codes. I know "for (string word, int numb, ; cin>>word>>numb; )" is not working. just trying to let you know what I am trying to do. My goal is to declare two types of variables with the same lifetime and cin them together. Other way of coding is helpful too. thanks in advance.

#include <iostream>
#include <vector>
#include <string>
#include <utility>
using namespace std;
int main ()
{
    cout<<"enter a word and a number"<<endl;
    for (string word, int numb, ; cin>>word>>numb; )
    {
        //do some work      
    }
return 0;
}

ok, I think this is the closest I can get as someone suggested.

#include <iostream>
#include <vector>
#include <string>
#include <utility>
using namespace std;
int main ()
{
    vector<pair<string,int> > pvec;
    cout<<"enter a word and a number"<<endl;
    {
        int numb=0; 
        for (string word; cin>>word>>numb; )
            pvec.push_back(make_pair(word,numb));
    }
    cout<<pvec[3].second<<endl;
return 0;
} 

Answer 1

This is not possible. You can declare two variables of the same basic type in the initialization statement in the for loop, but you cannot declare two variables of different basic types. You have to declare one outside of the for loop.

Answer 2

About the nearest you can get is:

int main ()
{
    cout<<"enter a word and a number"<<endl;
    {
        string word;
        for (int numb; cin>>word>>numb; )
        {
            //do some work      
        }
    }
    return 0;
}

The extra set of braces limits the scope of word similarly to the way the loop limits the scope of numb. Clearly, you could reverse the declarations; it might be better (more symmetric) to use:

int main ()
{
    cout<<"enter a word and a number"<<endl;
    {
        string word;
        int numb;
        while (cin>>word>>numb)
        {
            //do some work      
        }
    }
    return 0;
}

Since there is no increment or initialize operation, the code is really a while loop with a couple of declared variables; this achieves the same result and works.

Answer 3

I'm fairly certain it's not possible to declare 2 variables of 2 different types in a for statement, but I also fail to see the advantage to doing so over something like this:

int main ()
{
    cout<<"enter a word and a number"<<endl;
    while( cin.good() )
    {
        string word;
        int num;

        cin >> word >> num;
        //do some work      
    }
    return 0;
}

In general I prefer to use for loops where there is something to count or at least iterate over. Other situations should be using a while or do loop.

Answer 4

The way you are trying to do it is not the cleanest way. I'd do it like this:

string word;
int num;
while(true)
{
    cin >> word >> num;
    if (!cin.good()) break;
    // do some work
}

word and num are in the same scope (same "lifetime")

Note that you'd want to substitute the while(true) with some suitable condition.

---

If you want word and num to be inside the scope of the loop do something like:

while(true)
{
    string word;
    int num;
    cin >> word >> num;
    if (!cin.good()) break;
    // do some work
}

OR

{
    string word;
    int num;
    while(true)
    {
        cin >> word >> num;
        if (!cin.good()) break;
        // do some work
    }
}

I don't know why this would be necessary though.

Answer 5

The following is untested, but should work:

int main()
{
  std::cout << "enter a word and a number" << endl;
  for (struct { std::string word, int number } vars;
       std::cin >> vars.word >> vars.number;
      )
  {
    //do some work      
  }
  return 0;
}