Basics Question

Write a program to count digit in a number

 public class Main
 {
     public static int countDigit(int num){
         int count= (int)(Math.log10(num)+1);
         return count;
     }
     public static void main(String[] args) {
         System.out.println(countDigit(1345));//4
         System.out.println(countDigit(112));//3
         System.out.println(countDigit(1));//1
         System.out.println(countDigit(12));//2
     }
 }

Write a program to reverse a number.

 public class Main
 {
     public static int reverseNumber(int num){
         int temp=num;
         int reverseN=0;
         while(temp!=0){
             int lastDigit= temp%10;
             reverseN=reverseN*10+lastDigit;
             temp=temp/10;
         }
         return reverseN;
     }
     public static void main(String[] args) {
         System.out.println(reverseNumber(5446));
     }
 }

Write a program to check whether number is armstrong or not.

An Armstrong number (also known as a narcissistic number) is a number that is equal to the sum of its own digits each raised to the power of the number of digits. For example:

153 is an Armstrong number because 13+53+33=1531^3 + 5^3 + 3^3 = 15313+53+33=153.

9474 is an Armstrong number because 94+44+74+44=94749^4 + 4^4 + 7^4 + 4^4 = 947494+44+74+44=9474.

 public class Main
 {
     public static boolean armstrongCheck(int num){
         int temp= num;
         int sum=0;
         int numberOfDigit= (int)(Math.log10(num) + 1);
         while(temp!=0){
             int lastDigit= temp%10;
             sum= sum+ (int)(Math.pow(lastDigit,numberOfDigit));
             temp=temp/10;
         }
         if(sum==num)
         return true;
         else
         return false;
     }
     public static void main(String[] args) {
         System.out.println(armstrongCheck(1634));//true
         System.out.println(armstrongCheck(35));//false
         System.out.println(armstrongCheck(1));//true
         System.out.println(armstrongCheck(123));//false
         System.out.println(armstrongCheck(120));//false
         System.out.println(armstrongCheck(0));//true
     }
 }

Write a program to print all the divisors of a number.

 public class Main
 {
     public static void printDivisor(int n){
         for(int i=1; i*i<=n;i++){
             if(n%i==0) {
             System.out.println(i);
             if((n/i)!=i){
             System.out.println(n/i);
              }
         }
         }

     }
     public static void main(String[] args) {
         printDivisor(27);//1 27 3 9

     }
 }

Write a program to check whether entered number is prime or not.

 public class Main
 {
     public static boolean checkPrime(int num){
         if(num<2){
             System.out.println("Number is not prime");
         }else{
             boolean flag= true;
             for(int i=2; i*i<=num;i++){
                 if((num%i)==0){
                     flag=false;
                 }
             }
             if(flag==true)
             return true;
             else
             return false;
         }
         return true;
     }
     public static void main(String[] args) {
         System.out.println(checkPrime(2));//true
         System.out.println(checkPrime(5));//true
         System.out.println(checkPrime(52));//false
         System.out.println(checkPrime(7));//true
     }
 }

Write a program to find the highest common factor(HCF) of numbers.

 public class Main
 {
     public static int findingHcf(int a, int b){
         while(a!=b){
             if(a>b)
             a=a-b;
             else
             b=b-1;
         }
         return a;
     }
     public static void main(String[] args) {
         System.out.println(findingHcf(1,5));//1
         System.out.println(findingHcf(11,55));//11
         System.out.println(findingHcf(2,4));//2
     }
 }