C Program to Convert Decimal to Binary using Array

In this article, we will write a C program to convert a decimal number to binary with the help of an array.

The program takes an integer from the user, converts it into its equivalent binary number and prints the result on the screen.

Sample Input:

Enter a number: 27

Sample Output:

The Binary Equivalent is: 11011

Before writing the actual program, let’s first see how you get the binary equivalent of a decimal number.

To convert a decimal number to a binary number, you can follow these steps:

  • Divide the decimal number by 2.
  • Write down the integer quotient (the result of the division) and the remainder (either 0 or 1).
  • If the quotient is greater than 0, repeat steps 1 and 2 using the quotient as the new decimal number.
  • Write down the remainders in reverse order to get the binary number.

Let’s follow all these steps and write the actual program:

// C program to convert decimal
// to binary using Array

#include <stdio.h>

int main() {
    int num, count = 0, arr[100];
    printf("Enter a number: ");
    scanf("%d", &num);
    // Repeat until num becomes zero
        arr[count] = num % 2;  // Remainder
        num = num / 2;  // Quotient
    printf("The Binary Equivalent is: ");
    for(int i = 0; i < count; i++){
        // Print the bits in reverse order
        printf("%d", arr[count-i-1]);
    return 0;


Enter a number: 27
The Binary Equivalent is: 11011

Code Explanation:

Here is a brief explanation of how the above program works:

  1. Declare integer variables “num”, “count” and an integer array “arr” of size 100.
  2. Prompt the user to enter a decimal number using the printf() function.
  3. Read the input number from the user using the scanf() function and store it in the “num” variable.
  4. Initialize “count” to 0.
  5. Use a while loop to convert the decimal number “num” into its binary equivalent using the following steps:
    • Compute the remainder of “num” divided by 2 using the modulus operator (num % 2) and store it in the next index of “arr”.
    • Update the value of “num” to be equal to the quotient of “num” divided by 2 using integer division (num / 2).
    • Increment the value of “count” by 1.
    • Repeat the above three steps until “num” becomes 0.
  6. Use a for loop to print the binary equivalent stored in the “arr” array in reverse order using the following steps:
    • Loop from 0 to count-1.
    • Access each element of the “arr” array in reverse order using the index (count-i-1).
    • Print each bit using printf() function.

That’s how it works. Thanks for reading!


  • Manoj Kumar

    Hi, My name is Manoj Kumar. I am a full-stack developer with a passion for creating robust and efficient web applications. I have hands-on experience with a diverse set of technologies, including but not limited to HTML, CSS, JavaScript, TypeScript, Angular, Node.js, Express, React, and MongoDB.

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