Why this cin is not working properly?

Question

#include <iostream>
#include <map>
#include <string>

using namespace std;

int main (void)
{

    int c;
    cout<<"enter number of test cases\n";
    cin>>c;
    while (c!=0)
    {
        string s;
        int t;
        cout<<"enter number of strings to be entered\n";
        cin>>t;
        map <string,int> a;
        map <string,int>::iterator it;    
        while ( t!= 0 )
        {
            getline(cin,s);
            it = a.find(s);
            if ( it == a.end() )
            {
                a.insert(pair<string,int>(s,1));
                cout<<"New inserted\n";
            }
            else
            {
                a[s]++;
                cout<<"Value incremented\n";
            }
            t--;
        }
        it = a.begin();
        cout<<"Value will print\n";
        while ( it != a.end() )
        {
            cout<<it->first<<" "<<it->second<<"\n";
            it++;
        }
        c--;
    }
    return 0;
}

So, I made this code which first asks for test cases, and then asks for number of strings and then sorts the strings and outputs their frequency. Now, in this code, as soon as I hit enter after entering the number of strings, the message New Inserted is displayed, meaning that the new line is being put as a string in the map. Why is that happening?

Thanks!

PS: I tried putting fflush(stdin) before getline but it doesnt help either.

I removed `stdio.h` and used `cin` in place of `scanf` ( which I did only as an attempt to make it work ) but it still doesn't. — sarah, Sep 25 '14 at 14:59
Next time, please prepare an [MCVE](http://stackoverflow.com/help/mcve). The whole problem could have been summarized in a 10-line program. — Csq, Sep 25 '14 at 15:12

Csq · Answer 1 · 2014-09-25T15:05:17.013

1

scanf reads the number from the input, and leaves a newline character behind. That newline is interpreted by the next getline, and you get an empty line at first.

Fix 1: read the newline with scanf:

instead of reading the number only:

scanf("%d", &t);

use the following which swallows the newline as well:

scanf("%d\n", &t);

Anyway, it is a bad idea to mix stdio with iostream but you'd get a similar same result if you would use

cin >> t;

Fix 2 (works with streams as well): Ignore the first line read by getline

Fix 3

Use getline to get the numbers into strings and parse them:

getline(cin, s);
istringstream ( s ) >> t;

edited Sep 25 '14 at 15:05

answered Sep 25 '14 at 14:59

Csq

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I didn't get you. Do you suggest placing an additional `scanf` after getting the number of strings. Btw, even if you put, `cin` instead of `scanf`, it still doesn't work. – sarah Sep 25 '14 at 15:01
@sarah updated to be more precise – Csq Sep 25 '14 at 15:02
But, why does this happen? I have removed `stdio` but it doesn't solve the problem. I can remove the first line, but why does this happen in the first place? – sarah Sep 25 '14 at 15:02
That's in the first sentence of the answer. – Csq Sep 25 '14 at 15:03
I am asking, does it happen with cin as well? Does cin shows a similar nature? – sarah Sep 25 '14 at 15:05
@sarah Yes, it does. – Csq Sep 25 '14 at 15:06

Why this cin is not working properly?

1 Answers1