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Maybe the title isn't what it should, or maybe its a duplicate, but either way,i'm stuck and couldnt find the right answer here or anywhere else.

I`m used to php, and recently started learning c++.

I need to convert a php loop that loops trough a julian date/time. In php this is quite easy.

In php i just create a variable with the julian date/time and then start looping with decimal numbers. An example:

<?php

    $jd = 2445874.74375;

    for($x=0; $x<=300; $x++) {
        echo "new jd = ". $jd;
        $jd = $jd + 0.5; // half a day
    }

?>

Which then result in the following number sequence

jd = 2445874.74375
jd = 2445875.24375
jd = 2445875.74375
jd = 2445876.24375
jd = 2445876.74375
jd = 2445877.24375
jd = 2445877.74375
jd = 2445878.24375
jd = 2445878.74375

I'm new to c++, so i just tried to copy the same thing but changed the syntax so it compiles and runs in C++.

int main() {

    double jd = 2445874.74375; // I figured i need a double here?

    for(int i = 0; i <= 300; i+=1) {

        cout << jd << endl;

        jd = jd + 0.5;
    }
}

But when i run the code, the results show a total different number then i would expect. From what i understand and read, the number doesn't really change, but is formatted differently... Output looks like this ->

2.44587e+06
2.44588e+06
2.44588e+06
2.44588e+06
2.44588e+06
...
2.44589e+06

But i need a number like the original one. So what am i missing, what do i not understand and most importantly how can restore the number formatting like the original julian date/time number i inserted into the double? I need the jd like 2445874.74375 to appear in its original format to make another function work. So how i can make this loop working, like its working in php? I already noticed that in C++ defining a variables the right way seems to be very important, where as in php it seems to be less important. But either way, i don't get it. I have read about integers, floating points, doubles, char and strings etc. But the more i look into it, the complexer it becomes for me...

Esocoder
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    I suggest you get a couple of books from [this curated list](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list/388282#388282) to read, and in general learn more about [C++ I/O manipulators](https://en.cppreference.com/w/cpp/io/manip). – Some programmer dude Jan 06 '19 at 12:02
  • Thats great intel! – Esocoder Jan 06 '19 at 15:59

1 Answers1

3

I was quite surprised by the result myself. Apparently cout outputs doubles in scientific notation by default. Using the std::fixed stream manipulator should fix it. 

int main()
{
    double jd = 2445874.74375; // I figured i need a double here?

    for (int i = 0; i <= 300; i += 1) {

        std::cout << std::fixed << jd << std::endl;

        jd = jd + 0.5;
    }
    system("pause");
}
DerDerrr
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