C Program to Convert Octal to Decimal: Full Code & Output

Converting numbers between systems is a skill you’ll use in both computer science and electronics. Here, we’re gonna convert an octal number, like 17, into its decimal form. Octal numbers are base-8, using digits 0-7, and decimals are base-10.

Prerequisites for the C Program to Convert Octal to Decimal

Before you start writing the program, ensure you know these:

• Understanding of loops such as while in C.
• Usage of basic mathematical operators like %, /, and *.
• Familiarity with <stdio.h> for input/output.
• Any C compiler such as GCC 9 or newer — or just run it in the EduSeekho online compiler.

Source Code of C Program to Convert Octal to Decimal

Here's the source code for converting an octal number to its decimal equivalent. It calculates the decimal value by processing each digit.

#include <stdio.h>

int main() {
    int octalNumber, decimalNumber = 0, base = 1, rem;

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

    // Convert octal to decimal
    while (octalNumber != 0) {
        rem = octalNumber % 10;
        decimalNumber += rem * base;
        base *= 8;
        octalNumber /= 10;
    }

    // Output the result
    printf("The decimal equivalent is: %d\n", decimalNumber);

    return 0;
}

Output of the Convert Octal to Decimal Program

When you run the program with an input, here's what you'll see:

Enter an octal number: 17
The decimal equivalent is: 15

Algorithm to Convert Octal to Decimal in C

Converting octal to decimal means evaluating each digit by its position. Here's the step-by-step algorithm this C program follows:

1. Read the octal number from the user.
2. Initialize decimalNumber to 0 and base to 1.
3. Repeat while octalNumber is not 0:
4. Get the last digit using octalNumber % 10.
5. Update decimalNumber by adding the product of the digit and base.
6. Multiply base by 8.
7. Remove the last digit from octalNumber by dividing by 10.

flowchart TD
  A([Start]) --> B[/Read octalNumber/]
  B --> C[decimalNumber = 0]
  C --> D[base = 1]
  D --> E{"octalNumber != 0?"}
  E -->|Yes| F[rem = octalNumber %% 10]
  F --> G[decimalNumber += rem * base]
  G --> H[base *= 8]
  H --> I[octalNumber /= 10]
  I --> E
  E -->|No| J([End])

How the C Program to Convert Octal to Decimal Works

Let's break down how each part of the code converts octal to decimal:

• #include <stdio.h>: Includes the standard input and output library for functions like printf and scanf.
• int main(): The main function where program execution begins.
• int octalNumber, decimalNumber = 0, base = 1, rem;: Declares variables for storing the octal number, the resulting decimal number, the base (initially set to 1), and remainder.
• scanf("%d", &octalNumber);: Reads an octal number input from the user and stores it in octalNumber.
• while (octalNumber != 0): Loops until all digits have been processed — a fundamental control structure for this conversion.
• rem = octalNumber % 10;: Gets the last digit of octalNumber.
• decimalNumber += rem * base;: Converts and accumulates the current digit's decimal value.
• base *= 8;: Updates the base for the next digit's place value in octal.
• octalNumber /= 10;: Removes the processed digit from octalNumber.
• printf("The decimal equivalent is: %d\n", decimalNumber);: Outputs the calculated decimal number.
• return 0;: Ends the program, returning zero as the status code.

Time and Space Complexity of the C Program to Convert Octal to Decimal

Evaluating the efficiency of converting octal to decimal helps understand its performance.

Time Complexity: O(n), where n is the number of digits in the octal number — for instance, 2 for 17. The while (octalNumber != 0) loop processes each digit once, so 3 digits means 3 rounds.

Space Complexity: O(1). The program uses a fixed number of variables — octalNumber, decimalNumber, base, and rem. There's no extra space needed beyond these few.

Key takeaway:Octal to decimal conversion’s all about assigning positional values to each digit and updating base as you go.

FAQs About C Program to Convert Octal to Decimal

Here's a collection of frequently asked questions about converting octal numbers to decimal in C.

Related Programs

If you found this program helpful, check out these related programs:

• C Program to Convert Octal to Binary with Example
• C Program to Convert Binary to Octal with Sample Output
• C Program to Convert Binary to Decimal with Code and Output
• C Program to Convert Binary to Decimal and Vice-Versa
• C Program to Convert Hexadecimal to Decimal

Conclusion

This program shows a cool way of using basic arithmetic to convert number systems. If this caught your interest, give converting binary to decimal a shot for more practice. Get the logic down, and you'll be set for more complex conversions.

Keep sharpening your C skills with quizzes on our platform. You can also check out the code in the EduSeekho online compiler anytime.