Sashurocks Sashurocks - 1 month ago 14
C Question

Variable value is not changing

This is my code for calculating primes.
Basically I take a number divide by all the previous primes that i calculated to check if it is a prime or not. I was not getting correct answer. I kept changing the code to figure out the mistake. I found that i value is not initializing to 0 whenever it enters the loop. Instead i is 1,2,3. I cannot understand why this is happening. I'm using visual studio c.
Please explain why is this happening ???

#include<stdio.h>
#include<conio.h>
int main()
{
int primes[10000];
int i,j,k;
int primecheck;
primes[0]=2;

k=1;
for(j=3;;j+=2)
{
primecheck = 1;
i=0;
for(i=0;i<k;i++);
{

printf("%d\n%d\n%d\n",i,j,j%primes[i]);// this helped me figure
// out the problem
if(j%primes[i] == 0)
{
primecheck = 0;
printf (" %d, %d\n",j,primes[i]);
}
printf("%d\n",k);

}
if (primecheck == 1)
{
primes[k]=j;
printf("%d prime is %d\n",k+1,primes[k]);
k++;
if(k == 5)
{
break;

}
}
}
printf("%d",primes[k-1]);
getch();


}

Answer

Don't use the dummy loop.

for(i=0;i<k;i++);

Remove the semicolon at the end and try. For current code its not entering the below the section under above for loop for any iteration, it is treated as a dummy loop instead. So just try

for(i=0;i<k;i++)
{

}
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