The following table provides few examples of prime numbers.
Number
Divisor
Result
13
1, 13
Prime Number
15
1, 3, 5, 15
Not a Prime Number
47
1, 47
Prime Number
Using for loop
In the following example, we will check whether the given number (7) is a Prime number or not using for loop.
Example
Java Compiler
public class myClass
{
public static void main(String[] args)
{
int num =7;
int i =1;
int count =0;
for(i=1; i<=num; i++)
{
if(num % i ==0)
count++;
}
if(count ==2)
System.out.format("%d is a prime number", num);
elseSystem.out.format("%d is not a prime number", num);
}
}
Output
7 is a prime number
Using while loop
In the following example, we will check whether the given number (7) is a Prime number or not using while loop.
Example
Java Compiler
public class myClass
{
public static void main(String[] args)
{
int num =7;
int i =1;
int count =0;
while(num >= i)
{
if(num % i ==0)
count++;
i++;
}
if(count ==2)
System.out.format("%d is a prime number", num);
elseSystem.out.format("%d is not a prime number", num);
}
}
Output
7 is a prime number
Using do while loop
In the following example, we will check whether the given number (7) is a Prime number or not using do while loop.
Example
Java Compiler
public class myClass
{
public static void main(String[] args)
{
int num =7;
int i =1;
int count =0;
do {
if(num % i ==0)
count++;
i++;
}while(i <= num);
if(count ==2)
System.out.format("%d is a prime number", num);
elseSystem.out.format("%d is not a prime number", num);
}
}
Output
7 is a prime number
Prime Numbers between the Given Range
In the following example, we will find all the Prime numbers between 1 and 20.
Example
Java Compiler
public class myClass
{
public static void main(String[] args)
{
int start =1;
int end =20;
int count =0;
int i =1;
System.out.println("Prime numbers between 1 and 20:");
for(start=start; start<=end; start++)
{
for(i=1; i<=start; i++)
{
if(start % i ==0)
count++;
}
if(count ==2)
System.out.print(start +" ");
count =0;
}
}
}
Output
Prime numbers between 1 and 20:
2 3 5 7 11 13 17 19
Check Whether the Given Number is Prime or Composite
In the following example, we will check whether the given number is a Prime number or Composite number.
Example
Java Compiler
import java.util.Scanner;
public class myClass
{
public static void main(String[] args)
{
Scanner reader =new Scanner(System.in);
System.out.print("Enter a (int) Number: ");
int num = reader.nextInt();
int i;
int count =0;
for(i=1; i<=num; i++)
{
if(num % i ==0)
count++;
}
if(count ==2)
System.out.format("%d is a prime number", num);
elseSystem.out.format("%d is a composite number", num);
}
}
Output
Enter a (int) Number: 17
17 is a prime number
Reminder
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