Find the sum of all the prime numbers
A friend of mine who is learning to program in C, was having diffculty in writing a program to find the sum of all the prime numbers between a specified limit (in her case 360). I helped her out with the program, and I thought I'll post it here which might help others.
Code: C

Re: Find the sum of all the prime numbers
well this code is good but it ll take more time(for computational work)
please check this code the 2nd for loop Code:
/* ** Program to find the sum of all numbers between 3 and 60 ** @author : Pradeep ** @date : 11/29/2006 */ //where n verey big(though within the limits of int :) ) // then the checkin condition from to n/2 will take lot of time // suppose ur n==100 then it will check from n=2 to n=50 //so the no. of checking loops required for 100 will be 48 //where as if we go from n=2 to n= 10 we only require 8 loops so it will be much faster // now think for the case of n=1000 wouldnt it will take lot of time 
Re: Find the sum of all the prime numbers
I understood your point, but I see you have used sqrt() ! How does that help?? And we need to check whether it got a factor execpt for itself and 1 or not.

Re: Find the sum of all the prime numbers
I would use
t = sqrt(i); in for(j=2;j<=sqrt(i);j++) e.g. for(j=2;j<=t;j++) So it does not need to calc square root all the time it loops through j 
Re: Find the sum of all the prime numbers
yes i got you!
the thing is we dont need to go more than the sqrt of the no. which to be checked as prime if it is not divisibe by any no. upto sqrt(n) than there wont be any factor above that you can check it for any no. 
Re: Find the sum of all the prime numbers
Its not using square root anywhere, and neither does it require too. Could you please tell me why does it need to use square root??

Re: Find the sum of all the prime numbers
good point shabbir

Re: Find the sum of all the prime numbers
Quote:

Re: Find the sum of all the prime numbers
For example, sqrt(60) = 7.46, that means we will loop 7 times, but 60 is divisible by 30 also.
The program works fine with sqrt, but what is the logic? 
Re: Find the sum of all the prime numbers
But 30 is the largets no. The smallest you will find is less than the sqrt(n).
For logic refer http://en.wikipedia.org/wiki/Prime_number Finding prime numbers section 
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