Sashurocks - 4 months ago 29

C Question

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++)
{
}
```