Re: iterator on for loop with multiple ending conditions

From:

nathnn@gmail.com

Newsgroups:

comp.lang.c++.moderated

Date:

12 Dec 2006 17:44:42 -0500

Message-ID:

<1165949881.242844.79140@n67g2000cwd.googlegroups.com>

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If you want both of the terminating conditions in your for loop to
terminate you out of the loop i.e
testIndex<3 , vi!=testyVec.end()

then you need to change the above code to the following:

testIndex<3 && vi!=testyVec.end()

and your program will look like this.

The syntax with the comma is a correct syntax but it does not behave
like you want it to.

#include <iostream>
#include <vector>
using namespace std;

void main()
{
        int testIndex=0;
        vector<int> testyVec;
        testyVec.push_back(1);
        testyVec.push_back(2);
        testyVec.push_back(3);
        testyVec.push_back(4);
        testyVec.push_back(5);

       typedef vector<int>::iterator vecIterator;
        vecIterator vi;

        for(vi=testyVec.begin(); testIndex<3 &&
vi!=testyVec.end();++vi)
        {
           cout<<"itr: testIndex is "<<testIndex<< " and testyVec item
is "<<(*vi)<<"\n";
           testIndex++;
       }

}

janeywit wrote:

Hi,
I'm no expert in C++ and I've quite a while tracking down a problem
which I believe I am summarising here. If anybody can help me out I'd
be very grateful!
The following piece of code doesn't work as I expect:

        int testIndex=0;
        vector<int> testyVec;
        testyVec.push_back(1);
        testyVec.push_back(2);
        testyVec.push_back(3);
        testyVec.push_back(4);
        testyVec.push_back(5);

       typedef vector<int>::iterator vecIterator;
        vecIterator vi;

        for(vi=testyVec.begin(); testIndex<3, vi!=testyVec.end();
++vi)
        {
           cout<<"itr: testIndex is "<<testIndex<< " and testyVec item
is "<<(*vi)<<"\n";
           testIndex++;
       }

I expect the for loop to end after 3 iterations due to one of the
ending conditions "testIndex<3". It doesn't. It goes on until the
second ending condition is reached. In fact if I switch the order of
the ending conditions then it always ignores the first one. Am I
using incorrect syntax... is there some bug ... or what am I missing?!
(I know I can do this by putting && between the two conditions but I
thought the other syntax was also correct?)
Thank you!
Jane

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