Help: datatypes...

Discussion in 'C++' started by Dala Dahlgren, Nov 4, 2006.

  1. I am writing a program where I have a subroutine which adds up a number,
    basically something like this;

    int myNumber;

    void add(int i){

    So everytime "add" is called myNumber increases.

    My problem is that myNumber is "reset" or is definet as "infinity", even
    though the number is not too large for the datatype used.
    I have tried with a couple of different datatypes.
    First I defined all my numbers as "double" since I don't only add integers.
    But when myNumber is about 6000 it is suddenly set to #INF the next time it
    I have also tried to define the numbers as pure integers ("long"), but now
    the number is reset to 0 a little after it passes 600,000.

    Both the 'double' and the 'long' datatypes should be able to handle larger
    numbers than this. I am using Microsoft Developer Studio 97, on a Pentium 4

    Can somebody tell me what my problem is and what I should do to be able to
    add up more numbers?

    Dala Dahlgren, Nov 4, 2006
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  2. Dala Dahlgren

    Ian Collins Guest

    Only if you post a small compilable example that demonstrates your
    problem. Otherwise all people can do is guess. Building the example
    code may show you the cause.
    Ian Collins, Nov 4, 2006
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  3. Dala Dahlgren

    Salt_Peter Guest

    I'm not getting the same behaviour. Can you maybe show how you are
    calling the function. We can only guess at what value is passed to the
    function. Are you sure you aren't invoking a factorial?
    Also, is myNumber initialized before use. See below.
    #include <iostream>
    #include <limits>

    int myNumber(0);

    void add(int i)
    myNumber += i;

    int main()
    // study numeric limits
    std::cout << "max integer = " << std::numeric_limits< int >::max()
    << std::endl;
    std::cout << "max long = " << std::numeric_limits< long >::max() <<
    std::cout << "max double = " << std::numeric_limits< double >::max()
    << std::endl;

    for(int i = 0; i < std::numeric_limits< int >::max(); ++i)
    add(1); // this will take a while

    std::cout << "myNumber = " << myNumber << std::endl;
    return 0;

    max integer = 2147483647
    max long = 9223372036854775807
    max double = 1.79769e+308
    myNumber = 2147483647 // <- result concurs with an integer's limits
    Salt_Peter, Nov 4, 2006
  4. Dala Dahlgren

    BobR Guest

    Salt_Peter wrote in message ...

    Ever try to 'print' that double max() on windows, in 'fixed' format?
    [ this is on win98, MinGW(GCC 3.3.1 ]

    // int main(){
    std::string DblMax("");
    std::eek:stringstream out;
    out.precision( 400 );
    out.setf( std::ios_base::fixed );
    // cout<<"out.precision()="<<out.precision()<<std::endl; // =190
    // note output: out.precision()=190

    // out<<std::numeric_limits<double>::max(); // GNU/Linux OK

    // - biggest I could get to 'print' -
    double tmp( std::numeric_limits<double>::max() / 1.0e+276);
    // max() / 1.0e+275==boom

    std::cout <<"DblMax=out.str() = "<<DblMax<<std::endl;
    // } // main()
    /* -- output --
    DblMax=out.str() =

    On GNU/Linux, it prints the whole freakin' max() number.


    Different compiler? Try it. Or, am I just missing something?

    Obviously ms-window$ was not involved to get us to the moon! <G>
    BobR, Nov 4, 2006
  5. Dala Dahlgren

    Salt_Peter Guest

    Sorry, no windows here. linux FC5, gcc 4.1.1 x86_64, FX dual-core.
    Which explains the output above.
    And yes, it prints the whole thing. And i do mean the *whole* thing.
    If you don't mind, i'll spare the newsgroup.
    Salt_Peter, Nov 4, 2006
  6. Dala Dahlgren

    Steve Pope Guest

    Have you tried "long long"? I've seen systems where "long"
    is no longer than "int", but "long long" is twice as long.
    I think this is for historical reasons.

    Steve Pope, Nov 5, 2006
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