C++ Program not working as expected.

[Stefano]

Hi,

For college I have to write this program in C++:

 

 

Assignment 3 – Skript-Aufgabe 69 (4 points)

The number π can be defined through various infinite sums. Here are two of them.  

 

π / 4  = 1 – 1/3 + 1/5 – 1/7 ...

 

π / 2 = 1 + 1/3 + (1*2) / (3 * 5) + ( 1 * 2 * 3 ) / ( 3 * 5 * 7) + ...
Write a program for computing an approximation of π, based on these formulas. Which formula

is better for that purpose?

 

I have written this program here that outputs π using both methods, but it doesn't work.

 

 

#include <iostream>

int main()
{
    std::cout << "Number of cycles n=? ";
    unsigned int n;
    std::cin >> n;
    
    //Method 1
    double a = 0.0;
    unsigned int s = 1;
    while (s != (n+1))
        {
            if (s % 2 == 0)
                a += (1/(2*s - 1));
            else
                a -= (1/(2*s - 1));
            ++s;
        }
    a *= 4;
    std::cout << a << "\n";
    
    //Method 2
    a = 1;
    unsigned int t = 1;
    unsigned int b = 1;
    for (unsigned int x = 0; x != (n+1); ++x)
        {
            t *= x;
            b *= ( ( 2 * x ) + 1);
            a += ( t / b );
        }
    
    a *=2;

    std::cout << a << "\n";
    
    return 0;
}

Can any of you see the mistake? All help is appreciated.

 

PS. I'm coding in X-Code if that helps.

 

[Nineshadow]

What exactly doesn't working?
Any debugger? 

[Stefano]

What exactly doesn't working?

Any debugger?

Whatever the input is, it output 4 for the first method and 2 for the second.

[fizzlesticks]

You're doing integer divisions, making s a float or double would fix that.

Edit: Scratch that, it would make the modulus too annoying, just cast to a float before dividing.

[Stefano]

You're doing integer divisions, making s a float or double would fix that.

Edit: Scratch that, it would make the modulus too annoying, just cast to a float before dividing.

Cheers.

[Ciccioo]

i think that the first method will give you -π, the if() condition should be inverted