C Program To Convert Octal to Decimal

In this tutorial, i am going to show you how to convert octal numbers to decimal numbers in c programs using functions.

Algorithm to Convert Octal to Decimal

Follow the below given algorithm to write a program to convert octal numbers to decimal numbers; as follows:

  • Take an input octal number from user and stored in an int type variable say octal.
  • Create A function, which name convert().
    1. Digits of octal are extracted one by one starting from right.

                     int rem = octal%10;

                2. Extracted digits are multiplied with proper base i.e. power of 8.

                     int res = rem*pow(8,i);

                3. After multiplying each digit with proper base the results are added and stored in another variable say decimal.

                    decimal += res;

  • Call Convert function with parameters.
  • The output is printed.

C Program To Convert Octal to Decimal

    #include <stdio.h>
    // Function to convert octal number to decimal
    int convert(int octal)
        int decimal = 0, i = 0;
        //converting octal to decimal
        while (octal != 0)
            int rem = octal % 10;
            octal /= 10;
            int res=rem*pow(8,i);
            decimal += res;
        return decimal;
    //main program
    int main()
        int octal;
        printf("Enter an octal number: ");
        //user input
        scanf("%d", &octal);
        //calling function
        int decimal=convert(octal);
        //printing output
        printf( " %d in octal = %d in decimal", octal, decimal);     
        return 0;

The result of the above c program; as follows:

Enter an octal number: 120255
120255 in octal = 41133 in decimal

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