syntax/logic errors

[abrown07]

What are the syntax/logic errors in this code? I am confused between the two types.

[code]

int i;
double pi;

pi = 1.0;

for (i=2; i<n, i=i+1)
{
if (i%2 = 1)
pi = pi - (1.0 / ((2.0*i)+1));
else
pi = pi + (1.0 / ((2.0*i)+1));
}

pi = pi * 4.0;


[code]/*



also how can I make the output more accurate?

[whodgson]

int i;
double pi;
pi = 1.0;
for (i=2; i<n, i=i+1)//; missing  n? not declared
{
if (i%2 = 1)                              // == equality operator required
   pi = pi - (1.0 / ((2.0*i)+1));  
  else
   pi = pi + (1.0 / ((2.0*i)+1));
}
pi = pi * 4.0;
 

[donbock]

A syntax error is a violation of the C language standard; it triggers a compiler error. A logic error is a violation of what you want the program to do.

The most significant logic error is that you don't have any comments describing what this code snippet is supposed to do. Without a clear statement of your intentions it is difficult to say whether the code accomplishes them.

It looks like you are using a partial geometric series to approximate the value of pi. If so, the second term is missing and all terms except the first have the wrong sign.

[donbock]

I think your intention is to approximate the value of pi by evaluating the series
pi/4 = 1 - 1/3 + 1/5 - 1/7 + 1/9 - ...
(I was mistaken in my earlier post to characterize this as a geometric series.)

There are other techniques that are more efficient (ie, converge faster in fewer iterations). Take a look at Numerical approximations of pi in Wikipedia or do a google search.