# C Program to Convert Binary Number to Octal and vice-versa

To understand this example, you should have the knowledge of the following C programming topics:

## Program to Convert Binary to Octal

In this program, we will first convert a binary number to decimal. Then, the decimal number is converted to octal.

``````#include <math.h>
#include <stdio.h>
int convert(long long bin);
int main() {
long long bin;
printf("Enter a binary number: ");
scanf("%lld", &bin);
printf("%lld in binary = %d in octal", bin, convert(bin));
return 0;
}

int convert(long long bin) {
int oct = 0, dec = 0, i = 0;

// converting binary to decimal
while (bin != 0) {
dec += (bin % 10) * pow(2, i);
++i;
bin /= 10;
}
i = 1;

// converting to decimal to octal
while (dec != 0) {
oct += (dec % 8) * i;
dec /= 8;
i *= 10;
}
return oct;
}
``````

Output

```Enter a binary number: 101001
101001 in binary = 51 in octal
```

## Program to Convert Octal to Binary

In this program, an octal number is converted to decimal at first. Then, the decimal number is converted to binary number.

``````#include <math.h>
#include <stdio.h>
long long convert(int oct);
int main() {
int oct;
printf("Enter an octal number: ");
scanf("%d", &oct);
printf("%d in octal = %lld in binary", oct, convert(oct));
return 0;
}

long long convert(int oct) {
int dec = 0, i = 0;
long long bin = 0;

// converting octal to decimal
while (oct != 0) {
dec += (oct % 10) * pow(8, i);
++i;
oct /= 10;
}
i = 1;

// converting decimal to binary
while (dec != 0) {
bin += (dec % 2) * i;
dec /= 2;
i *= 10;
}
return bin;
}
``````

Output

```Enter an octal number: 67
67 in octal = 110111 in binary
```