c++ generating a double between 2 doubles

Question

So I need to randomly generate a double between 2 doubles, and in this specific case, it is to randomly generate a GPA. I tried at first to do this:

srand(time(NULL));

double rands1 = rand() % (4) + ((rand() % (10)) / 10.0);

And this does work... mostly. I can get anywhere from a 0.0 to 3.9, but it has to be from 0.0 to 4.0 inclusive! Changing the 4 in the code to a 5 can give 4.1 and higher as well however, and that is no good.

My question is, what would be a more efficient way to code this? I apologize if there is a pretty straight forward answer/if this seems simple, but I am pretty new to coding and c++. Thank you!

Possible duplicate of [Generating random integer from a range](https://stackoverflow.com/questions/5008804/generating-random-integer-from-a-range) — Software2, Jul 19 '17 at 22:09
You can always regard, 0.0 - 4.0 inclusive as the integers 0 to 40. Do the division after, when appropriate. — Captain Giraffe, Jul 19 '17 at 22:09
@CaptainGiraffe yup, by far the most efficient way to handle this problem. thank you! — J.Einhorn, Jul 19 '17 at 22:27

score 1 · Accepted Answer · answered Jul 19 '17 at 22:18

If it's just to find a gpa to one decimal place, you can find an int between 0 and 41 then divide by 10 to get a decimal. For example:

double rand2 = (double)(rand()%41)/10;

rand()%41 will generate a number that is between 0 and 40 inclusive. Then we cast it as a double and divide by 10. So if the generated number is 34, we get 3.4 as a double.

To use other double as the range, you would just multiply them by the number of decimal places you want following the number, then also divide by that number

//Range== 0,34 with 3 decimal places    
double rand2 = (double)(rand()%35000)/1000;

this is definitely the easiest way for me to follow, I should've thought more about the actual math of it rather than try to have perfect code. Thank you very much!! — J.Einhorn, Jul 19 '17 at 22:25

c++ generating a double between 2 doubles

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