LearningNote

Q2a:

#include<stdio.h>

int main()
{
    int i,j,flag;
    for(i=1;i<=1000;i++)
    {
        flag=0;
        for(j=2;j<i;j++)
        {
                if(i%j==0)
                {
                        flag=1;
                }
        }
        if(flag==0)
        {
                printf("%d is a prime.\n",i);
        }
   }
    return 0;
}


Q2b:

#include<stdio.h>

int main()
{
    int i,j,flag,count=0;
    for(i=1;i<=1000;i++)
    {
        flag=0;
        for(j=2;j<i;j++)
        {
            if(i%j==0)
            {
                flag=1;
            }
        }
        if(flag==0)
        {
        count++;
        }
    }
    printf("There are %d primes in 1~1000.\n",count);
    return 0;
}



Q2c:

#include<stdio.h>

int main()
{
    int i,j,flag,sum=0;
    for(i=1;i<=1000;i++)
    {
        flag=0;
        for(j=2;j<i;j++)
        {
            if(i%j==0)
            {
                flag=1;
            }
        }
        if(flag==0)
        {
            sum=sum+i;
        }
    }
    printf("The sum of all primes in 1~1000 is %d.\n",sum);
    return 0;
}