Question:
I have to do a program on alternating sums using vectors. I am not sure how to start this program. I thought about using an array and every even index add the value and every odd index subtract the value. Does that sound right? Any ideas?

The only good way to do this is to figure it out yourself. You've thought about using an "array," but didn't you just mention "vectors"? You might have correctly described your algorithm; now you just need to implement it.

I have what sounds like the same assignment and yes that will work. If this is the same assignment, use a vector because the assignment specifies this type. Then, test for evens and odds. The first index is zero which is even so add evens and subtract odds.

wat exactly do u mean by alternating sums using vectors??

An alternating series is one in which the sign flip-flops. For example,

4 + 4/3 + 4/5 + 4/7 + 4/9 + 4/11 + 4/13

is not an alternating series. But the following is:

4 - 4/3 + 4/5 - 4/7 + 4/9 - 4/11 + 4/13

I think the original poster wants to take a vector containing

[ a b c d e f g h ... ]

and compute

a - b + c - d + e - f + g - h + ...

then wat he is doing sounds correct

Below is my source code but I am getting errors stating invalid conversions. Any ideas?





#include <iostream>
#include <cmath>
#include <cstdlib>
#include <vector>
using namespace std;

double alternating_sum(vector<double>);

int main()
{


double num_values = 0;

while (true)
{
cout << " Enter a real number (CTRL-D to quit): ";
cin >> num_values;
}
vector<double> num_sum(num_values);
double altsum_of_vector = 0;
altsum_of_vector = alternating_sum(num_sum);

cout << " The alternating sum of the vector is " << altsum_of_vector << endl;

return 0;
}


double alternating_sum(vector<double> v)
{
double sum = 0;
if (v.size() == 0)
{
return 0;
}

else
{
for (int i = 0; i < v.size(); i++)
{
if ( (i % 2) == 0)
{
sum += v[i];
}
else
{
sum -= v[i];
}
}
}
return sum;
}

>Below is my source code but I am getting errors stating invalid conversions.
Post the errors.

Below is the error message I am receiving.


p9-2.cpp: In function `int main()':
p9-2.cpp:31: warning: passing `double' for argument 1 of `std::vector<_Tp,
_Alloc>::vector(unsigned int) [with _Tp = double, _Alloc =
std::allocator<double>]'
[hs001@cs hs001]$

That's a warning, not an error. It's telling you that the constructor expects an unsigned int, but you're passing a double, and there may be a loss of data in the conversion.