Wrong logic in approximating e^1 :( [closed] - c++

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I've written code using class object to calculate the value of e^1 by approximation using the summation of series given below, but seems like i can't get the logic to work properly.I tried running it to 5 terms for approximation but my answer was 1.2 only where it should be around 2.7038...
e^1 is given by the series 1 + 1/1! + 1/2! + 1/3! ...
#include <iostream>
#include <stdlib.h>
using namespace std;
class factorial
{
public:
double loopfactorial ( double y)
{
double value;
for (int a=0; a<=y; a++)
{
value=1;
value = value*a;
}
return value;
}
};
int main()
{
factorial calcu;
int x;
double sum;
cout<<"Enter the number of terms to approximate exponent:"<<endl;
cin>>x;
for (int y=1; y<=x-1; y++)
{
int n = calcu.loopfactorial(y);
sum=1.0;
sum = sum + 1/n;
}
cout<<"The value of e is "<<sum<<endl;
return 0;
}

Answer 1

For reference and the benefit of future readers, here's the "correct" code:
#include <iostream>
#include <cstdlib>
int main()
{
unsigned int terms;
if (!(std::cout << "Number of terms: " && std::cin >> terms))
{
std::cout << "Error, I did not understand you.\n";
return EXIT_FAILURE;
}
double e = terms > 0 ? 1.0 : 0.0, term = 1.0;
for (unsigned int n = 1; n < terms; ++n)
{
term /= n;
e += term; // this is "e += 1/n!"
}
std::cout << "e is approximately " << e << "\n";
}
(The code can be trivially extended to compute ex for any x.)

Answer 2

You should move the variable initializations out of the loops - you're resetting them over and over.
Side note: it's rather pointless to put loopfactorial in a class.

Answer 3

I found three problems with your code, both are similar to each other
1. in loopfactorial(), value=1 should be defined before the loop body
2. in main(), sum=1.0 should be defined before the loop body
3. in loopfactorial(), loop variable a should have been initialized with either 1 or 2 instead of 0.

Answer 4

Try moving your initial values outside the loop:
#include <iostream>
#include <stdlib.h>
using namespace std;
class factorial
{
public:
double loopfactorial ( double y)
{
double value;
// MOVED INITIAL VALUE HERE
value=1;
for (int a=1; a<=y; a++)
{
value = value*a;
}
return value;
}
};
int main()
{
factorial calcu;
int x;
double sum;
cout<<"Enter the number of terms to approximate exponent:"<<endl;
cin>>x;
// MOVED INITIAL VALUE HERE
sum=1.0;
for (int y=1; y<=x-1; y++)
{
int n = calcu.loopfactorial(y);
sum = sum + 1/n;
}
cout<<"The value of e is "<<sum<<endl;
return 0;
}