C Program to Convert Octal to Decimal

Octal to Decimal conversion in C:

We can convert any octal number(base-8 (0 or 7)) into decimal number (base-10 (0 to 9)) by c program.

Decimal Number

Decimal number is a base 10 number because it ranges from 0 to 9, there are total 10 digits between 0 to 9. Any combination of digits is decimal number such as 23, 445, 132, 0, 2 etc.

Octal Number

Octal number is a base 8 number because it ranges from 0 or 7. Any combination of digits (0 yo 7) is Octal number such as 34, 54, 77, 210 etc.

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

C Functions
C User-defined functions

/* Program to Convert Octal to Decimal */

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

long long convertOctalToDecimal(int octalNumber);
int main()
    int octalNumber;

    printf("Enter an octal number: ");
    scanf("%d", &octalNumber);

    printf("%d in octal = %lld in decimal", octalNumber, convertOctalToDecimal(octalNumber));

    return 0;

long long convertOctalToDecimal(int octalNumber)
    int decimalNumber = 0, i = 0;

    while(octalNumber != 0)
        decimalNumber += (octalNumber%10) * pow(8,i);

    i = 1;

    return decimalNumber;


Enter an octal number: 14
14 in octal = 12 in decimal

Enter an octal number: 77
77 in octal = 63 in decimal

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