# C Program to Convert Octal Number to Decimal Number System

• Write a C program to convert octal number to decimal number system.
• How to convert octal number to binary number.

#### Required Knowledge

Octal number system is a base 8 number system using digits 0 and 7 whereas Decimal number system is base 10 number system and using digits from 0 to 9. Given an octal number as input from user convert it to decimal number.

##### For Example
2015 in Octal is equivalent to 1037 in Decimal number system.

Algorithm to convert Octal to Decimal number
• We multiply each octal digit with 8i and add them, where i is the position of the octal digit(starting from 0) from right side. Least significant digit is at position 0.
Let's convert 2015(octal number) to decimal number
Decimal number = 2*83 + 0*82 + 1*81 + 5*80 = 1024 + 0 + 8 + 5 = 1037

## C program to convert a octal number to decimal number

```#include <stdio.h>
#include <math.h>

int main() {
long octalNumber, decimalNumber=0;
int position=0, digit;

printf("Enter an Octal Number\n");
scanf("%ld", &octalNumber);

/* Converting octal number to decimal number */
while(octalNumber!=0) {
/* get the least significant digit of octal number */

digit = octalNumber%10;
decimalNumber += digit*pow(8, position);

position++;
octalNumber /= 10;
}

printf("Decimal Number : %ld", decimalNumber);

return 0;
}
```
Output
```Enter an Octal Number
2015
Decimal Number : 1037
```
```Enter an Octal Number
1234
Decimal Number : 668
```

Related Topics