Thread: Closest prime number in an array?

Code:

#include <stdio.h>

int main(){
int N,min,max,i,j,temp;


printf ("Enter N.\n"); scanf ("%d",&N);


int polje[N];


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


printf ("Enter %d. number:\n",i+1); scanf ("%d",&temp);
polje [i] = temp;
}


i=0;
max = polje[i];


for (i=1;i<N;i++)
if (polje[i]>max) max = polje[i];


i=0;
min=polje [i];


for (i=1;i<N;i++)
if (polje[i]<min) min = polje[i];


printf ("%d is biggest, and %d smallest.\n",max,min);


// Find and print out only the closest prime number to the max
//Need help here...


return 0;
}

google "c code generate prime numbers"

What's the plan to find this prime number? Two options pop out:

1) find all the primes < the max number, and keep the highest one

2) begin testing the odd numbers (in decreasing value), starting with max-1 (or -2 if max is even), and find the prime that way.

The Sieve of Eratosthenes is well suited for #1, and Trial by division method is best suited for #2.

Wikipedia has a good article on the Sieve of E.

Can you look this code? i wrote this at past, and finds all the prime number dividers of a number.You can use the d[i] array and a for loop to calculate your max prime number and the second max prime number.Deal with your codes

Code:

#include <stdio.h>




p(int asal)
{
int y=1;


int i4;
for(i4=2;i4<asal;i4++)
{
if (asal%i4==0)
{
y=0;
}
else
y=1*y;
}
return y;
}




int main()
{
int x,i,i1,i2,r;
int f=0;
int c[100];
int a=1;
int si=0;
int cntr=0;
int kontrol=1;
int d[100];
int ix=0;


for(i1=0;i1<=50;i1++) c[i1]=0;


printf("enter a number");
scanf("%d",&r);




for(i1=0;i1<=100;i1++)
{
c[i1]=0;
}
x=r;
for(i=2;i<=x; )
{
si=si+1;
if(si%20==0) i++;


if ((x%i==0)&&(p(i)==1))
{
c[f]=i;
f++;
x=x/i;


}
else
{
i++;
x=r;
}
}
printf("\nbolenleri:");


for(i2=0;i2<=99;i2++)
{


if ((c[i2]>1))
{
d[ix]=c[i2];
printf(" %d, ",d[ix]);
cntr++;
ix++;
}
}
for(i=0;i<cntr;i++)
{
i2=i+1;
for( ;i2<cntr;i2++)
{
if (d[i]==d[i2]){
kontrol=0;
}
else
kontrol*=1;
}
}
if (kontrol==1)
printf("\nCarpanlari arasinda, ayni asal sayi yoktur.(there are no same prime number divider ");
else
printf("\nCarpanlari arasinda, ayni asal sayidan bulunmaktadir.(there are more than 1 same prime number dividers ");




scanf("%d",&a); 


}

Originally Posted by rac1

Can you look this code?

Indent the code properly

Then I'll look at it.