exponents

[joeshmoe1337]

I am kinda new to C and was wondering how would i do
2 to the power of n and then subtract one.

thank you

[kermit]

you could use the pow() function:

it would look something like this

pow(base, n); /* in your case pow is the function call, base would be 2
                 and n is whatever number you want to raise it to */

When you have that number, it is relatively easy to subtract 1 from it.

to use pow() make sure you #include math.h, and if you are using gcc, be sure to the -lm flag to link the math library.

pow returns a double, so be sure to keep that in mind when you use it.

~/

[iwabee]

pow is unnesseserry here, he only wants power of 2. If n is less than 31 then:

unsigned int answer, n = SOMETHING;

answer = ~(0xFFFFFFFF<<n);

[Thantos]

Bitwise operations should not be used in place of pow(). What happens if the integer is a negative, is a 64 bit number, is a 128 bit number. What if they want to use 3 instead of 2, or negitive 2, or a negative power.

Use pow() and save yourself a lot of trouble.

[MrWizard]

Also important, what if they want to raise a real value to an exponent. Shifting certainly won't work.

edit: I know he said 2 raised to n , but still thought it should be mentioned.