CODEWITHSUNDEEP
c++vectoriteratoraverage
Rivten
Rivten

Reputation: 43

Interator and average in C++

I'm trying to learn to use iterator with vectors in C++ by, for example computing the average of a vector.

Yet this code does not give the proper answer and I cannot figure out why !

double average(vector<double> const &v)
{
    vector<double>::size_type taille = v.size();
    double sum = 0;
    for(vector<double>::const_iterator i = v.begin(); i != v.end(); ++i)
        sum += v[*i];

    return sum/taille;
}

Can anybody give me a hint ?

Thanks a lot in advance ! Bye :)

Upvotes: 0

Views: 5933

Answers (3)

JBarberU
JBarberU

Reputation: 1029

The iterator actually points to the object. Proper way to iterate is:

double average(vector<double> const &v)
{
    vector<double>::size_type taille = v.size();
    double sum = 0;
    for(vector<double>::const_iterator i = v.begin(); i != v.end(); ++i)
        sum += *it;

    return sum/taille;
}

In C++11 you can do this too:

double average(vector<double> const &v)
{
    double sum = 0;
    for(const double &d : v)
        sum += d;

    return sum/v.size();
}

Upvotes: 1

Sarfaraz Nawaz
Sarfaraz Nawaz

Reputation: 361532

In C++, iterators imitate the behaviors of pointers (to some degree). So if it is an iterator to an element, you access the element by dereferencing it as *it.

That means, instead of this:

sum += v[*i];

you should write this:

sum += *i; //just dereference the iterator!

Hope that helps.

Upvotes: 4

nullptr
nullptr

Reputation: 11058

Accessing vector items through an iterator is simply *i, not v[*i]. The form you've used requires accessing with index:

for (size_t i = 0; i < v.size(); i++) sum += v[i];

And your code should look like:

for(vector<double>::const_iterator i = v.begin(); i != v.end(); ++i)
    sum += *i;
          ^^^^ note this

Upvotes: 1

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