STL

[QueenJJ]

I have this question from one of my assignments

int main(int argv, char* argc[])
{
int i;
list<int> l;
do {
cin >> i;
l.push_back(i);
} while (i!=0);
return 0;
}

Adapt the above code, so that it alternately reads ints and strings from cin, and stores them in two separate lists

I can adapt is so it reads ints and strings from cin and stores them in two separate lists but I can't seem to do it alternatively.

I need to read it alternatively for a follow on question.

[Ganado]

Something like:

int counter = 0;

do {

    if (counter % 2 == 0) // counter is even
    {
        // read int, store it in list<int>
        int num;
        cin >> num;
        int_list.push_back(num);

        if (num == 0)
            break; // i.e. "while (i != 0)" in original code
    }
    else // counter is odd
    {
        // read string, store it in list<string>
        string str;
        cin >> str;
        string_list.push_back(str);
    }

    counter ++;

} while (true);

Not sure if there is sentinel logic for the string input, you can add that by breaking there, too.

% is "modulus", which you can think of as being the remainder.
Odd numbers and even numbers alternate, so you can use this to determine to ask for an int or a string.

Strictly speaking, you don't need the counter variable, you could alternate based on the current sum of the sizes of the two lists, but I thought this would be easier to digest.

[jonnin]

Kiss it. There are times when the above alternation technique is needed, and times when you can just unroll the alternation inside the loop.

int i;
string s;
do
{
  cin >> i; 
   int_list.push_back(i);
  cin >> s;
  str_list.push_back(s);
}
while(something);

[QueenJJ]

Thank you very much

Following you reply this is what I currently have.

#include <list>
#include <string>
#include <iostream>
using namespace std;


int main(int argv, char* argc[])
{
list<int> l;
list<string> s;
int counter = 0;
do {
if (counter % 2 == 0) //counter is even
{
//read int and store in list<int>
int num;
cin >> num;
l.push_back(num);

if (num == 0);
break;
}
else // counter is odd
{
//read string and store in list<string>
string str;
cin >> str;
s.push_back(str);
}

counter++;

} while (true);

}

However, when I try to run it, it exits after one input. I am not sure if I am doing something wrong.

[whitenite1]

@QueenJJ

if (num == 0);
Try removing the semi-colon on the above line in your code. The semi-colon terminates the statement.

[Ganado]

I agree with jonnin, would be simpler to just ask for a string and int every loop, breaking early if necessary.

[QueenJJ]

Thank you very much, problem solved