Trying to calculate Pi

Question

To calculate Pi you can use the equation pi/4=1-(1/3)+(1/5)-(1/7)+... Multiply it by 4 and you get Pi I created a formula to calculate each step of the equation relative to its position 1/(2n-1) and wrote code for it

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char** argv) 
{
    double p = 0;
    double pi = 0;
    int j = 1;

    do 
    {
        if (j % 2 == 1)
        {
            p = p + (1 / (2 * j - 1));
        }
        else
        {
            p = p - (1 / (2 * j - 1));
        }
        pi = p * 4;

        printf("%lf\n", pi);

        j++;
    } while (j < 10);

    return (EXIT_SUCCESS);
}

but it is only putting out 4.0000 Why? I cant find the mistake I made.

Answer 1

In the statement p = p + (1 / (2 * j - 1)); expression (1 / (2 * j - 1) yields in integer. To get expected result make either operand as floating type i.e either 1.0 or (float)(2 * j - 1)

Replace the statement

p = p + (1 / (2 * j - 1));/* 1/(2*j-1) results in integer, you won't get expected result */

with

p = p + (1. / (2 * j - 1));/* 1. means making floating type */