Question

Write the algorithm of program that evaluates the series 5-10+7+15+9- 20+11+25+... up to x terms, where the value of x is taken as input from the user. For example, the sum of the given series up to 3 terms should give 2 as output (5-10+7=2), similarly, the sum of this series up to 4 terms should give 17 as output (5-10+7+15=17), etc.

Answer 1

#include <iostream>
using namespace std;

int main()
{
int x;
cin>>x;
int c=1;
int e=5,o=10;
int sum=0;
  
for(int i=1;i<=x;i++)
{
if(i%2==0)
{
if(c==-1)
{
  
c=1;
}
else
{
  
c=-1;
}
  
sum=sum+o*c;
o=o+5;
}
else
{
sum=sum+e;
e=e+2;
}
  
  
  
}
cout<<sum;

return 0;
}