# C Program to Convert Decimal Number to Octal Number using Function

Here is a C program to convert a decimal number to octal number. Decimal number system is a base 10 number system using digits for 0 to 9 whereas octal number system is base 8 and using digits from 0 to 7. Given a decimal number as input from user we have to print the octal equivalent of input decimal number.

For Example:
100 in Decimal is equivalent to 144 in Octal number system.

Algorithm to convert Decimal to Octal number
• Divide the input decimal number by 8 and store the remainder.
• Store the quotient back to the input number variable.
• Repeat this process till quotient becomes zero.
• Equivalent octal number will be the remainders in above process in reverse order.
For Example:

Suppose input decimal number is 525
Step 1. 525/8 , Remainder = 5, Quotient = 65
Step 2. 65/8 , Remainder = 1, Quotient = 8
Step 3. 8/8 , Remainder = 0, Quotient = 1
Step 4. 1/8 , Remainder = 1, Quotient = 0
Now, the Octal equivalent of 525 is the remainders in reverse order : 1015

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

```#include <stdio.h>

long decimalToOctal(long n);
int main() {
long decimal;
printf("Enter a decimal number\n");
scanf("%ld", &decimal);
printf("Octal number of %ld is %ld", decimal, decimalToOctal(decimal));

return 0;
}

long decimalToOctal(long n) {
int remainder;
long octal = 0, i = 1;

while(n != 0) {
remainder = n%8;
n = n/8;
octal = octal + (remainder*i);
i = i*10;
}
return octal;
}
```
Output
```Enter a decimal number
1234
Octal number of 1234 is 2322
```

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

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

long octalToDecimal(long n);
int main() {
long octal;
printf("Enter an octal number\n");
scanf("%ld", &octal);
printf("Decimal number of %ld(Octal) is %ld", octal, octalToDecimal(octal));

return 0;
}

long octalToDecimal(long n) {
int remainder;
long decimal = 0, i=0;
while(n != 0) {
remainder = n%10;
n = n/10;
decimal = decimal + (remainder*pow(8,i));
++i;
}
return decimal;
}
```
Output
```Enter an octal number
45132
Decimal number of 45132(Octal) is 19034
```

Related Topics