In this tutorial, we will write a C program to convert a binary number into octal using a while loop. Before that, you must have knowledge of the following topics in C.

**Binary number**

The binary numbers are based on 0 and 1, so it is a base 2 number. They are the combination of 0 and 1. For example, 1001, 110101, etc.

**Octal number**

The octal numbers are the numbers with base 8 and use the digits 0 to 7. Example: 8 in decimal is represented as 10 in octal, 25 as 31, and so on.

**Example**:

`Input: `

`101001`

Output: `51`

Let us go through a program for the Binary to Octal Conversion in C.

**C Program to Convert Binary to Octal**

**Source Code:** convert binary to octal using a function in C

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | #include <stdio.h> #include <math.h> int conversionFunc(int binaryNum) { int octalNum = 0, decNum = 0, i = 0; while (binaryNum != 0) { decNum += (binaryNum % 10) *pow(2, i); ++i; binaryNum /= 10; } i = 1; while (decNum != 0) { octalNum += (decNum % 8) *i; decNum = decNum / 8; i *= 10; } return octalNum; } int main() { int binaryNum; printf("Enter a binary number: "); scanf("%d", &binaryNum); printf("Octal Equivalent Value: %d", conversionFunc(binaryNum)); return 0; } |

**Output:**

`Enter a binary number: 101001`

Octal Equivalent Value: 51