In this post, we will learn **how to convert octal to binary using C** Programming language.

This program will take an octal number as input from the user and convert it into a binary number using a user-defined function.

So, without further ado, letâ€™s begin this tutorial.

**C Program To Convert Octal To Binary**

// C Program To Convert Octal To Binary #include <stdio.h> #include <math.h> long octalToBinary(int num){ int decimal = 0, i = 0; long binary = 0; while (num != 0){ decimal = decimal + (num % 10) * pow(8, i); i++; num = num / 10; } i = 1; while (decimal != 0){ binary = binary + (decimal % 2) * i; decimal = decimal / 2; i = i * 10; } return binary; } int main(){ int num; // Asking for Input printf("Enter an octal number: "); scanf("%d", &num); printf("Equivalent Binary number is: %ld", octalToBinary(num)); return 0; }

**Output**

```
Enter an octal number: 25
Equivalent Binary number is: 10101
```

**How Does This Program Work ?**

` `**int num;**

In this program, we have declared an int data type variable named as **num**.

` `** // Asking for Input
printf("Enter an octal number: ");
scanf("%d", &num);**

Then, the user is asked to enter an octal number. The value of this octal number will get stored in the **num** named variable.

` `** printf("Equivalent Binary number is: %ld", octalToBinary(num));**

Now, we call our custom defined function named **octalToBinary** which converts octal numbers into binary numbers.

**long octalToBinary(int num){
int decimal = 0, i = 0;
long binary = 0;
while (num != 0){
decimal = decimal + (num % 10) * pow(8, i);
i++;
num = num / 10;
}
i = 1;
while (decimal != 0){
binary = binary + (decimal % 2) * i;
decimal = decimal / 2;
i = i * 10;
}
return binary;
}**

This function will first convert the **octal number into a decimal number**, and then convert the **decimal number into a binary number**.

**Conclusion**

I hope after going through this post, you understand **how to convert octal to binary using C **Programming language.

If you have any doubt regarding the program, feel free to contact us in the comment section. We will be delighted to help you.

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