Thread: STL Vector problem with code

Lets write something closer to real C++ code. I've put the comments inside the code for convenience.

Code:

#include <iostream>
#include <vector>

using namespace std;

int main() {
    // In C++ we don't declare all variables up front at the start of our function.
    // instead the normal thing to do is to declare them near their point of first use.
    // That way, if we were to say exit this function say when the user entered a negative
    // number then the program wouldn't have wasted time initialising the vector. Not too
    // important here obviously, but it can become very important in a larger program.
    int numberOfElements = 0;

    // A while loop was not appropriate here. That's because you intended the loop to
    // always be run at least once. The way to do that is not to assign a value to make
    // the condition true beforehand, but to make it a "do .. while" instead. That's what
    // they're for! In this instance a for (;;) loop with a break statement would work at
    // least as well too though, and save testing for the same condition twice.
    do {
          cout << "How many numbers will you be entering?" << endl; 
          cin >> numberOfElements;
          cin.ignore();
          
          if (numberOfElements <= 0) {
              // You had two semi-colons on this line before.
              cout << endl << "Error... Please enter a positive integer" << endl;
          }
    } while (numberOfElements <= 0);
    
    cout << " Enter the numbers:\n\t\t\t";
    // Why use \n all of a sudden instead of endl? endl doesn't have to go at the end
    
    // The vector only gets initialised once we reach this line.
    vector<int> array;
    // vectors already keep track of how many items they contain. You're not supposed to
    // also track it separately in a variable of your own. Simply use the .size() method to find
    // out how many items it holds. arrayNumber and the finished flag were not needed.
    while (array.size() < numberOfElements) {
         int temp; // Nothing outside this loop needs to even know temp existed, so here is a good place for it.
         cin >> temp;
         array.push_back(temp);
         cin.ignore();
    }

    // sum and loopNumber can be declared here. as loopNumber is just a for-loop
    // counter the normal thing to do is to declare it inside the for loop. Personally
    // I would use a shorter name.
    float sum = 0;
    // It's safer to use array.size() here in case the code changes later.
    for (size_t loopNumber = 0; loopNumber < array.size(); loopNumber++) {
        sum += array[loopNumber];
    }
    // Serious C++ programmers would replace the loop above with one call to std::accumulate
    
    // Also pay attention to the clean use of whitespace in this code vs what was posted earlier
    cout << "Average equals: " << sum / numberOfElements;
    cin.get();
}

P.S. The grammatical error in Elysia's sig always bothers me. ("every thing" should be "everything")
You don't have to feed Elysia's ego anyway

Real programmers would write std::vector<int>::size_t or shorter, std::size_t instead of int
int will give you signed/unsigned mismatch on VC++!

// Why use \n all of a sudden instead of endl? endl doesn't have to go at the endl

endl == '\n' + flush
What's the point of flushing in the middle of output?

Originally Posted by Elysia

Real programmers would write std::vector<int>::size_t or shorter, std::size_t instead of int
int will give you signed/unsigned mismatch on VC++!

Close. One would probably use a typedef for std::vector<int> and use something like IntVector::size_type.
<escuse> I daren't have compiled the code though, it's up to the person learning from it to find my bugs </escuse>

endl == '\n' + flush
What's the point of flushing in the middle of output?

A valid point. I wouldn't have put tabs after it myself, hence the endl would be on the end. I just didn't go so far as to say that the tabs should go.

Cleaning up other's code is like being a vacuum cleaner salesman. No matter how many people have vacuumed the same rug, you can always demonstrate how much more dirt your vacuum cleaner can lift out that other vacuum cleaners "missed".

jamort, a lot of people don't like block comments because they can't be nested.
And most IDEs have automatic line commenting/uncommenting for blocks of code.