Reverse-Number-in-Java
In this section, we will learn how to reverse a number in Java using while loop, for loop and recursion.
To reverse a number, follow the steps given below:
First, we find the remainder of the given number by using the modulo (%) operator.
Multiply the variable reverse by 10 and add the remainder into it.
Divide the number by 10.
Repeat the above steps until the number becomes 0.
There are three ways to reverse a number in Java :
Reverse a number using while loop Reverse a number using for loop Reverse a number using recursion Let’s apply the above steps in an example.
Example
Suppose, we want to reverse the number 1234.
In this example, we have taken three variables named number (the number to be reversed), remainder (stores the remainder), reverse (stores the reverse number) initialized 0.
Iteration 1:
number = 1234 remainder = 1234 % 10 = 4 reverse = 0 * 10 + 4 = 0 + 4 = 4 number = 1234 / 10 = 123 Now the value of the number and reverse variable is 123 and 4, respectively.
Iteration 2:
number = 123 remainder = 123 % 10 = 3 reverse = 4 * 10 + 3 = 40 + 3 = 43 number = 123 / 10 = 12 Now the value of the number and reverse variable is 12 and 43, respectively.
Iteration 3:
number = 12 remainder = 12 % 10 = 2 reverse = 43 * 10 + 2 = 430 + 2 = 432 number = 12 / 10 = 1 Now the value of the number and reverse variable is 1 and 432, respectively.
Iteration 4:
number = 1 remainder = 1 % 10 = 1 reverse = 432 * 10 + 1 = 4320 + 1 = 4321 number = 1 / 10 = 0 Now the variable number become 0. Hence, we get the reverse number 4321.
Let’s implement the above logic in a Java Program
Reverse a number using while loop
Output :
In the following program, we have replaced the while loop by a for loop. It also removes the last digit of the number, after each iteration. When the condition, number!=0 becomes false, the loop exits and we get the reversed number.
Output :
Reverse a number using recursion
Output :
The following program reverses both numbers, positive and negative. When we enter a number, it first checks the number is positive or negative. If the number is negative, it converts the number into positive by multiplying -1. After that, it performs the same steps (as we have performed in the above programs) to reverse a number. At last, again it checks the number is negative or positive. To make the number negative, it again multiplies the reverse number by -1.
Output :
