Need help writing function in c++?

Question

there are two function and they supposed to do following:

The sum of the powers of 2: 2^0 + 2^1 + 2^2 + ... + 2^(N-1)
The sum of the inverse of the powers of 2: 1/2^0 + 1/2^1 + 1/2^2 + ... + 1/2^(N-1)


In C++
Thx

? · Accepted Answer

There exists a simple formula for BOTH without resorting to using a loop.  I'll give you a hint:

2^0 + 2^1 + 2^2 + ... + 2^(N-1)

Think about it.  1+2+4+8...  2^4 is 16.  The answer for #1 is (2^N)-1.  This is useful for determining the maximum unsigned integer for its variable type.  maxnumber=pow(2,sizeof(int))-1, for example.  The reverse of this is ceil(log(maxnumber) / log(2)) = sizeof(int).. which is useful for determining how many bits you need when packing them tightly, such as:

struct color16bit { int r:5; int g:6; int b:5; }; //how else can u pack 3 ints into 16 bits?

vidhem · Answer

1.
void sumfun(int N)
{
double sum=0;
for(int iter=0;iter<N;iter++)
{
sum += pow(2,iter); //include Math.h in the header section
}

cout<<sum;
}

2.
void sumfun(int N)
{
double sum=0;
for(int iter=0;iter<N;iter++)
{
sum += pow(2,-iter); //include Math.h in the header section
}

cout<<sum;
}

? · Answer

You should at least take a stab at it, and come back with your attempts.  It's no fun for us to just write simple code for you.

Trending News

Need help writing function in c++?

3 Answers