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Hi, I have been trying to write a simple C++ program (using gcc 3.3.2) to find large prime numbers, which usually involves using the modulo (%) operator to check for factors. I need at least 11 significant digits to have adequate precision, but the int type apparently doesn't go that high. Is it possible to perform a modulo operation with floating point numbers, or alternatively, use ints with at least 11 significant digits?
You can't use the modulo operator on floating point numbers, but you can get an int with 11 significant digits. In gcc you just use the variable type long long (yes, 2 of them). This will get you a 64-bit integer which should be more than enough.
Thanks! For some reason, "long long int" still doesn't accept the numbers, but using drem() from the math.h package lets me calculate remainders with just a "double" datatype. I'll try it out and see how it goes.
Floating point operations sometimes create 'fuzz' - imprecise results way out at 8 or 10 decimal places. It's caused by floating point representations of odd numbers. When you are working with 12 digits of precision, you may bump into fuzz.
You will be much better of using an extended precsision library - why it was invented in the first place. double will not work for you reliably.