C Program To Convert Octal Number To Decimal Number, using While Loop

Lets write a C program to convert a number from Octal number system(base 8) to Decimal number system(base 10), using while loop.

Number Systems

1. Binary Number System uses base 2 and digits 01.
2. Octal Number System uses base 8 and digits 01234567.
3. Decimal Number System uses base 10 and digits 0123456789.
4. Hexadecimal Number System uses base 16 and digits 0123456789ABCDEF.

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Note: Octal number system can be derived by base 8 to the power of whole numbers.

Example:
etc .. 8⁴, 8³, 8², 8¹, 8⁰

etc .. 8⁴ = ‭4,096‬, 8³ = 512, 8² = 64, 8¹ = 8, 8⁰ = 1.

Expected Output for the Input

User Input:
Enter an Octal Number
24

Output:
Decimal Equivalent of 24 is 20.

Explanation:

If user enters num = 24.

(8³ x 0) + (8² x 0) + (8¹ x 2) + (8⁰ x 4 )
= 0 + 0 + (8 x 2) + (1 x 4)
= 16 + 4
= 20
So Decimal equivalent of Octal number 24 is 20.

Video Tutorial: C Program To Convert Octal Number To Decimal Number, using While Loop

Logic To Convert Octal Number To Decimal Number, using While Loop

In this C program we ask the user to enter / input an Octal number. Using while loop we calculate the reminder and add it to previous value of variable dec, along with pow(8, place). We make use of variable place to position the reminder.
dec = dec + rem * pow(8, place);

Source Code: C Program To Convert Octal Number To Decimal Number, using While Loop

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

int main()
{
    int num, dec = 0, rem = 0, place = 0;

    printf("Enter an Octal Number\n");
    scanf("%d", &num);

    printf("\nDecimal Equivalent of %d is ", num);
    while(num)
    {
        rem = num % 10;
        dec = dec + rem * pow(8, place);
        num = num / 10;
        place++;
    }
    printf("%d\n", dec);

    return 0;
}

Output 1:
Enter a decimal number
16

Octal Equivalent of 16 is 20

Output 2:
Enter an Octal Number
24

Decimal Equivalent of 24 is 20

Output 3:
Enter an Octal Number
132

Decimal Equivalent of 132 is 90

Output 4:
Enter an Octal Number
16

Decimal Equivalent of 16 is 14

Output 5:
Enter an Octal Number
40

Decimal Equivalent of 40 is 32

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