A prime number is a number that is divisible only by itself and 1. Write a program that asks a user for an integer value and the
n displays all prime numbers less than or equal to that number. For example, if the user enters 17, the program should display: Prime numbers less than or equal to 17:
System.out.print("Prime numbers less than or equal to " + number + " : ");
for(int i=2; i <= number; i++){
if(checkPrime(i)){
System.out.print(i + " ");
}
}
}
public static Boolean checkPrime(int num){
for(int i=2; i < num; i++)
{
if(num % i == 0){
return false;
}
}
return true;
}
}
Explanation:
Firstly, we create a function to check if a number is prime (Line 18 - 27).
This function will take one input value which is an integer, num.
To check if the input num is a prime, we can use modulus operator, %, to confirm if the num is divisible by any number starting from 2 to num - 1 (Line 19 - 24).
If the num is divisible by any number expect 1 and itself, it should equal to zero and return false to indicate it is not a prime number.
If all the num (except 1 and itself) is not divisible, the function will return true (Line 25).
Next, in our main program part (Line 3 - 16)
Prompt the user to input a number (Line 5 - 7)
Using a for-loop, we can keep calling the checkPrime() function by passing a current number (starting from 2 to input number) as argument (Line 12). The checkPrime() function will run and return true it the current number is prime, return false if it is not prime.
If the checkPrime() function return true, it will print the current number before proceed to the iteration of the for-loop to repeat the same check prime procedure (Line 13)
At the end all the prime numbers less than or equal to the input number will be printed out in the terminal