如何防止上一个矢量项打印？

Question

I am trying to prevent the last item of a vector from printing. How do I modify my code to make this happen?

void lAverage(){
    cout << endl << "The average of: ";
    for (int i = 0; i < gAverage.size(); ++i){
        if (i == gAverage.size()) {
            cout << gAverage[i]; // I have to modify something here.
        } else{
            cout << gAverage[i] << ", ";

        }
    }
    cout << " = " << average << endl;
}

instead of printing: the average of: 3, 2, 1, 0 = 2

I'd rather: The average of : 3, 2, 1 = 2

No comma on the last one and the 0 removed.

Answer 1

Just stop your iteration a step earlier:

int size = gAverage.size() - 1;
for (int i = 0; i < size; ++i){
    if (i == size - 1) {
        cout << gAverage[i];
    } else{
        cout << gAverage[i] << ", ";

    }
}
cout << " = " << average << endl;

Answer 2

There is no case where

(i == gAverage.size())

Because i is always smaller than gAverage.size() because the range of the for loop is from 0 .. until gAverage.size()-1

You should check

if (i == gAverage.size()-1)

Answer 3

If you want to print to an output stream with intervening commas, but at the same time exclude the last two item in the container (for whatever reason), here is a solution using the std::copy algorithm:

#include <algorithm>
#include <iterator>
#include <vector>

using namespace std;

void lAverage()
{
    // make sure there are at least 2 items
    if (gAverage.size() >= 2)
    {
        auto itLast = gAverage.end() - 2;
        cout << endl << "The average of: ";

        // copy item to output stream with intervening comma up until
        // two before the last item  
        copy(gAverage.begin(), itLast, ostream_iterator<int>(cout, ","));

        // print the item before the last and the average
        cout << *itLast << " = " << average << endl;
   }
}

Live Example

Answer 4

You need to iterate until you reach the element before the last one :

for (int i = 0; i < gAverage.size()-1; ++i){

and

if (i == gAverage.size()-2) {

careful, it's -2 because you'll never reach gAverage.size()-1

Answer 5

Two questions here: how to print one element less than the total number in the container, and how to make the last element printed not be followed by a comma.

To meet both requirements without using a conditional, I'd stop the loop two elements back

int last = gAverage.size() - 2;
for (int i = 0; i < last; ++i)
{
    cout << gAverage[i] << ", ";
}
cout << gAverage[last];

cout << " = " << average << endl;

The loop prints all values that will be followed by the comma. The next cout statement prints the second last element of the array.

This avoids the silliness of a condition in the loop to detect the last element being printed.