# 100 Prime Numbers Program

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### #1 almayhm

Reputation: 0
• Posts: 7
• Joined: 24-March 09

# 100 Prime Numbers Program

Posted 24 March 2009 - 11:29 AM

Hey guys, I made this program to generate the first 100 prime numbers starting from 1. Only thing I need help with is having the output print out horizontally, instead of a straight down list. Maybe like a break between every 30 numbers or so. Any form of help is greatl appreciated, thanks!

```//Allan Rodriguez

public class whileprime
{
public static void main(String args[])
{
int num = 4;
int count = 0;
System.out.println("First 100 Prime Numbers: ");
System.out.println("1");
System.out.println("2");
System.out.println("3");
while(count < 100)
{
num++;
if(num % 2 != 0)
{
int dv = 3;
while((num % dv != 0)&&(dv <= ((num - 1) / 2)))
{
dv++;
}
if(num % dv != 0)
{
count++;
System.out.println(num + "		 ");

}
}
}

}

}

--------------------Configuration: <Default>--------------------
First 100 Prime Numbers:
1
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97
101
103
107
109
113
127
131
137
139
149
151
157
163
167
173
179
181
191
193
197
199
211
223
227
229
233
239
241
251
257
263
269
271
277
281
283
293
307
311
313
317
331
337
347
349
353
359
367
373
379
383
389
397
401
409
419
421
431
433
439
443
449
457
461
463
467
479
487
491
499
503
509
521
523
541
547
557

Process completed.

```

Is This A Good Question/Topic? 0

### #3 Nat3TheGreat13

Reputation: 18
• Posts: 162
• Joined: 09-February 09

## Re: 100 Prime Numbers Program

Posted 24 March 2009 - 11:31 AM

Use
```System.out.print(num + "		 ");

```

### #4 almayhm

Reputation: 0
• Posts: 7
• Joined: 24-March 09

## Re: 100 Prime Numbers Program

Posted 24 March 2009 - 11:35 AM

Nat3TheGreat13, on 24 Mar, 2009 - 10:31 AM, said:

Use
```System.out.print(num + "		 ");

```

thanks!, is there a way to have it do the same but in groups of 10?

ex. output as follows:

1 29
2 31
3 37
5 41
7 43
11 47
13 53
17 59
19 61
23 67 ETC.

This post has been edited by almayhm: 24 March 2009 - 11:47 AM

### #5 mostyfriedman

• The Algorithmi

Reputation: 727
• Posts: 4,473
• Joined: 24-October 08

## Re: 100 Prime Numbers Program

Posted 24 March 2009 - 11:46 AM

btw 1 is not a prime number

### #6 mostyfriedman

• The Algorithmi

Reputation: 727
• Posts: 4,473
• Joined: 24-October 08

## Re: 100 Prime Numbers Program

Posted 24 March 2009 - 11:51 AM

here's a better algorithm for this, this is called the Sieve of eratosthenes algorithm
```import java.util.Scanner;

public class Primes
{
public static void generate(int x, int y)
{
boolean [] a = new boolean[y+1];
for(int i = 2; i < a.length; i++)
a[i] = true;

for(int i = 2; i*i <= y; i++)
{
for(int j = i; j*i <= y; j++)
{
a[i*j] = false;
}
}

for(int i = x; i <= y; i++)
if(a[i])
System.out.print(i + " ");
System.out.println();
}

public static void main(String[]args)
{
Scanner sc = new Scanner(System.in);
int x = sc.nextInt();
int y = sc.nextInt();
generate(x, y);
}
}

```

### #7 thebpf

Reputation: 4
• Posts: 42
• Joined: 19-March 09

## Re: 100 Prime Numbers Program

Posted 24 March 2009 - 04:20 PM

Create an array of type String to place the results in:

String primes[] = new String[10];
for (i=0 to 9)
for (j=0 to 9) // this is needed so you can get your 100 prime numbers
primes[i] = prime+"<tab>"

Then:
for(i=0 to 9)
System.out.println(primes[i]);

almayhm, on 24 Mar, 2009 - 10:35 AM, said:

thanks!, is there a way to have it do the same but in groups of 10?

ex. output as follows:

1 29
2 31
3 37
5 41
7 43
11 47
13 53
17 59
19 61
23 67 ETC.