C Program to Convert Octal Number to Decimal Number

June 5, 2021

This program converts an octal number to an equivalent decimal number.

Example: Program to Convert Octal to Decimal

In this program, we have created a user defined function for octal to decimal conversion. The program takes the octal number (entered by user) as input and converts it into a decimal number using function. To understand this program, you should have the knowledge of following C programming topics:

  1. C – User defined functions
  2. while loop in C
#include <stdio.h>
#include <math.h>
/* This function converts the octal number "octalnum" to the
 * decimal number and returns it.
long octalToDecimal(int octalnum)
    int decimalnum = 0, temp = 0;

    while(octalnum != 0)
        decimalnum = decimalnum + (octalnum%10) * pow(8,temp);
        octalnum = octalnum / 10;

    return decimalnum;
int main()
    int octalnum;

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

    printf("Equivalent decimal number is: %ld", octalToDecimal(octalnum));

    return 0;


Enter an octal number: 754
Equivalent decimal number is: 492