Write a C program to read Octal number from user and convert to Binary number system. How to convert from Octal number system to Binary number system in C. Logic to convert octal to binary number system in C program.

**Example**

**Input**

Input octal number: 172

**Output**

Binary of 172: 01111010

## Required knowledge

Must know - Program to find last digit

### Octal number system

Octal number system is a base 8 number system. It uses 8 symbols to represent all its numbers i.e. `01234567`

### Binary number system

Binary number system is a base 2 number system. It uses only two symbols i.e. 0 and 1 to represent all numbers.

## Logic to convert octal to binary

I have divided the octal to binary conversion in three steps:

- Extract last digit from octal number.
- Find binary equivalent of octal digit found above.
- Combine all converted binary together.

**Octal to Binary conversion table**

Decimal | Octal | Binary |
---|---|---|

0 | 0 | 000 |

1 | 1 | 001 |

2 | 2 | 010 |

3 | 3 | 011 |

4 | 4 | 100 |

5 | 5 | 101 |

6 | 6 | 110 |

7 | 7 | 111 |

### Algorithm to convert octal to binary

Algorithm Conversion from Octal to Binarybegin:read(octal);OCTALVALUES[] ← 0, 1, 10, 11, 100, 101, 110, 111;binary← 0;rem← 0;place← 1;While(octal> 0)begin:rem←octal% 10;binary← (OCTALVALUES[rem] *place) +binary;octal←octal/ 10;place←place* 1000;end;write('Binary ='binary);end;

## Program to convert octal to binary

```
/**
* C program to convert Octal number system to Binary number system
*/
#include <stdio.h>
int main()
{
int OCTALVALUES[] = {0, 1, 10, 11, 100, 101, 110, 111};
long long octal, tempOctal, binary, place;
int rem;
/*
* Input Octal number from user
*/
printf("Enter any Octal number: ");
scanf("%lld", &octal);
tempOctal = octal;
binary = 0;
place = 1;
/*
* Convert octal to binary
*/
while(tempOctal > 0)
{
// Extract the last digit of octal
rem = tempOctal % 10;
/*
* Get the binary equivalent of octal digit
* add it to the binary variable
*/
binary = (OCTALVALUES[rem] * place) + binary;
// Remove the last octal digit
tempOctal /= 10;
// Increase the place value
place *= 1000;
}
printf("Octal number = %lld\n", octal);
printf("Binary number = %lld", binary);
return 0;
}
```

Output

Enter any Octal number: 1720 Octal number = 1720 Binary number = 1111010000

Happy coding 😉

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- C program to convert Binary to Hexadecimal number system.
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