How do I avoid scientific notation for large numbers?

Question

I am doing 2^1000 and I am getting this:

1.07151e+301

Is there any way to actually turn this into a proper number without the e+301, or at least can anyone show me where I can see how to turn this in to a real number, by some way working with the e+301 part?

Answer 1

So, I'm thinking that what you really want is just the ability to print it without scientific notation. If you're using printf, what you want is:

printf( "%f1000.0", value );
// note that 1000 is way larger than need be,
// I'm just too lazy to count the digits

With cout, try something like:

cout.setf(ios::fixed);
cout << setprecision(0) << value;

If you want to print it as a power of two (2^1000 vs 10715...), you're on your own.

Answer 2

There is a practical limit to how large a number that can be directly manipulated in machine registers can be. if you are using double precision floats there are a total of 64 bits, some of which are devoted to the mantissa, some to the exponent, and 1 to the sign bit.

2^1000 needs a 1001 bit integer to be represented without losing precision. In order to work with numbers like that you will need to use a library that has big number support, such as GNU MP.

Answer 3

You need to use a number class specifically designed for long numbers.

To represent 2^1000 as an exact number then by definition you need a number format that actually holds 1001 binary bits. The longest normal primitive integer format is usually only 64 bits.

BTW, the answer is:

% perl -Mbigint -e 'print 2**1000'
10715086071862673209484250490600018105614048117055336074437503883703510511249361224931983788156958581275946729175531468251871452856923140435984577574698574803934567774824230985421074605062371141877954182153046474983581941267398767559165543946077062914571196477686542167660429831652624386837205668069376