# C program to convert Octal to Decimal number system

Write a C program to input Octal number from user and convert to Decimal number system. How to convert from Octal number system to Decimal number system in C program. Logic to convert octal to decimal number system in C programming.

Example

Input

`Input octal number: 172`

Output

`Decimal number: 122`

## Required knowledge

Must know – Program to find last digit of a number.

### Octal number system

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

### Decimal number system

Decimal number system is a base 10 number system. Decimal number system uses 10 symbols to represent all its numbers i.e. `0123456789`

## Logic to convert from octal to decimal ```Algorithm Conversion Octal to Binary
begin:
decimal ← 0; rem ← 0; place ← 0;
While(octal !=0)
begin:
rem ← octal % 10;
decimal ← decimal + (8place * rem);
octal ← octal / 10;
place ← place + 1;
end;
write('Decimal =' decimal);
end;```

## Program to convert octal to decimal number system

``````/**
* C program to convert Octal number system to Decimal number system
*/

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

int main()
{
long long octal, tempOctal, decimal;
int rem, place;

/* Input octal number from user */
printf("Enter any octal number: ");
scanf("%lld", &octal);
tempOctal = octal;

decimal = 0;
place = 0;

/*
* Convert octal to decimal
*/
while(tempOctal > 0)
{
/* Extract the last digit of octal */
rem = tempOctal % 10;

/* Convert last octal digit to decimal */
decimal += pow(8, place) * rem;

/* Remove the last octal digit */
tempOctal /= 10;

place++;
}

printf("Octal number = %lld\n", octal);
printf("Decimal number = %lld", decimal);

return 0;
}``````

Output

```Enter any octal number: 172
Octal number = 172
Decimal number = 122```

Happy coding 😉