Vector adding issues...

This is a discussion on Vector adding issues... within the C++ Programming forums, part of the General Programming Boards category; A few topics down I mentioned I was making a program that computes the average of an unspecified amount of ...

  1. #1
    Beginner in C++
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    Vector adding issues...

    A few topics down I mentioned I was making a program that computes the average of an unspecified amount of numbers. Here's what I have so far:

    Code:
    #include <iostream>
    #include <string>
    #include <stdexcept>
    #include <vector>
    using namespace std;
    
    int main()
    {
    	cout << "Enter the numbers you want to find the average of, followed by an end-of-file: ";
    	
    	double Num;
    	
    	// First vector. This holds the numbers the user has input.
    	
    	vector<double>Average1;
    	vector<double>& Avg1 = Average1;
    	
    	while (cin >> Num)
    	{
    		Avg1.push_back(Num);
    	}
    	
    	// Second vector. This holds the amount of numbers in the first vector
    	
    	typedef vector<double>::size_type Average2;
    	Average2 size = Avg1.size();
    	
    	// Throw an error if there aren't any numers if there aren't any values stored
    	
    	if (size == 0)
    	{
    		throw domain_error("Average of an empty vector");
    	}
    	
    	// Compute the average
    	
    	double Average3 = { ... I need to do this part ... } / size;
    	
    	cout << "The average of the numbers is: " << Average3;
    	
    	cin.get();
    	
    	return 0;
    }
    The problem I'm facing is adding the values together in the first vector. Say, for example, I had three numbers in there, and could only hold three. I would add them together like this:

    Code:
    double Average3 = (Avg1[0] + [Avg1[1] + Avg1[size - 1]) / size;
    If my indexes are wrong, please tell me because I've never used them before. Right, I obviously can't do the above in my program because I could be adding 2 numbers together, or 5 etc.

    Simply put, how do I add together the elements in Average1 without knowing what they are, and how many there are? If that's not possible, I'll try another approach.

    I welcome all criticism towards it, but please provide a solution.

    Thanks.

  2. #2
    (?<!re)tired Mario F.'s Avatar
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    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  3. #3
    Beginner in C++
    Join Date
    Dec 2007
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    I've never used Iterators, and don't yet know how to use them (only up to chapter 4 in Accelerated C++) Can you post the solution relevent to my program with an explanation please? I hate to ask, but I don't have my book on the C++ Standard library handy, and won't untill tomorrow night and I'd like to make changes to it during the course of tomorrow.
    Last edited by Caduceus; 02-02-2008 at 01:42 PM.

  4. #4
    (?<!re)tired Mario F.'s Avatar
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    I can but I will not Read the FAQ on doing homework.

    If you need to do this without iterators, use the size() member function and do a loop.

    Code:
    double total = 0;
    for (size_type i = 0; i != your_vector.size(); ++i) {
        total += your_vector[i];
    }
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  5. #5
    Beginner in C++
    Join Date
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    Thanks for the solution. This isn't actually homework, I was watching a beginner's video on youtube that made an average program with three numbers, and I just wondered how to do it with an unknown amount of numbers.

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