# Java: Convert a decimal number to binary numbers

## Java Basic: Exercise-19 with Solution

Write a Java program to convert an integer number to a binary number.

Decimal number: The decimal numeral system is the standard system for denoting integer and non-integer numbers. It is also called base-ten positional numeral system.

Binary number: In digital electronics and mathematics, a binary number is a number expressed in the base-2 numeral system or binary numeral system. This system uses only two symbols: typically 1 (one) and 0 (zero).

*Test Data:*

Input a Decimal Number : 5

**Pictorial Presentation: of decimal to binary number**

**Sample Solution:**

**Java Code:**

```
import java.util.Scanner;
public class Exercise19 {
public static void main(String args[]) {
// Declare variables to store decimal number, quotient, and an array for binary digits
int dec_num, quot, i = 1, j;
int bin_num[] = new int[100];
// Create a Scanner object to read input from the user
Scanner scan = new Scanner(System.in);
// Prompt the user to input a decimal number
System.out.print("Input a Decimal Number: ");
dec_num = scan.nextInt();
// Initialize the quotient with the decimal number
quot = dec_num;
// Convert the decimal number to binary and store binary digits
while (quot != 0) {
bin_num[i++] = quot % 2;
quot = quot / 2;
}
// Display the binary representation of the decimal number
System.out.print("Binary number is: ");
for (j = i - 1; j > 0; j--) {
System.out.print(bin_num[j]);
}
System.out.print("\n");
}
}
```

**Explanation:**

In the exercise above -

- First the code takes an integer or decimal number ('dec_num') as input from the user using the "Scanner" class.
- It initializes an array 'bin_num' to store the binary digits of the converted number and other necessary variables.
- Next it enters a loop to perform the decimal-to-binary conversion:
- In each iteration, it calculates the remainder of 'dec_num' when divided by 2 (which gives the least significant binary digit) and stores it in the 'bin_num' array.
- It then updates 'dec_num' by dividing it by 2 (which effectively shifts it to the right).
- The loop continues until 'dec_num' becomes zero, effectively converting the entire decimal number to binary.
- After the loop, it prints the binary representation of the decimal number by iterating through the 'bin_num' array in reverse order (from the most significant digit to the least significant digit).

Sample Output:

Input a Decimal Number : 5 Binary number is: 101

**Flowchart: **

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