Thread: std::accumulate

  1. #1
    Registered User
    Join Date
    Dec 2007


    I have a problem with this std::accumulate function. When compiling this I have quite much compile notifications but it compiles.
    One that says:

    warning C4244: '=' : conversion from 'double' to 'int', possible loss of data

    This is what is happening here. I have declared the elements in vector "vec" to doubles with 2 decimals.
    However the output of this will be 15 wich is an integer. The output should have been. (10,50 + 20,50 / 2) = 15,50.

    I wonder what I could be doing wrong since everything is declared to doubles. Where is the conversion from double to int that seems to be happening.

    #include <numeric>
    std::vector<double> vec(12);
    vec[1] = 10.50;
    vec[2] = 20.50;
    double sum = std::accumulate( vec.begin() + 1, vec.begin() + 3, 0);
    double Average = ( sum / (3 - 1)  );
    ofstream out;"C:\\test.txt");
    out << Average
    Last edited by Coding; 03-16-2008 at 05:44 PM.

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    The function template determine the type based on the initial value. 0 is an int literal, 0.0 is a double literal, so if you want to instantiate std::accumulate<double>, you would write:
    double sum = std::accumulate(vec.begin() + 1, vec.begin() + 3, 0.0);
    Actually, it's not std::accumulate<double>, but effectively std::accumulate<std::vector<double>::iterator, double>.
    Last edited by laserlight; 03-16-2008 at 06:04 PM.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
    Registered User
    Join Date
    Dec 2007
    okay, that was the thing... It worked fine.

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