Decimal to Octal Conversion in C

Decimal to Octal Conversion

Decimal to Octal conversion is the process of converting a decimal number (base-10) into its equivalent octal number (base-8). Each octal digit represents a power of 8.

For example, the decimal number 31 is equal to octal 37 because:

(3 × 8¹) + (7 × 8⁰) = 24 + 7 = 31

We will explore three methods to convert a decimal number to an octal number using C programming.

Method 1: Using Division by 8

We divide the decimal number by 8 repeatedly, storing the remainders. These remainders represent the digits of the octal number from least significant to most significant.

#include <stdio.h>

void decimalToOctal(int decimal) {
    int octal[50], i = 0;
    
    while (decimal > 0) {
        octal[i] = decimal % 8;
        decimal = decimal / 8;
        i++;
    }
    
    printf("Octal equivalent: ");
    for (int j = i - 1; j >= 0; j--) {
        printf("%d", octal[j]);
    }
    printf("\n");
}

int main() {
    int decimal;
    printf("Enter a decimal number: ");
    scanf("%d", &decimal);
    decimalToOctal(decimal);
    return 0;
}
            

Output:

Enter a decimal number: 31
Octal equivalent: 37

Method 2: Using printf Function

C has a built-in function printf which can directly print the octal representation of a decimal number using the format specifier %o.

#include  <stdio.h>

int main() {
    int decimal;
    printf("Enter a decimal number: ");
    scanf("%d", &decimal);
    
    printf("Octal equivalent: %o\n", decimal);
    return 0;
}
            

Output:

Enter a decimal number: 31
Octal equivalent: 37

Method 3: Using Recursion

We can convert a decimal number to octal recursively. The recursive function divides the number by 8 and prints the remainders, which form the octal digits.

#include <stdio.h>

void decimalToOctalRecursive(int decimal) {
    if (decimal == 0) {
        return;
    }
    
    decimalToOctalRecursive(decimal / 8);
    printf("%d", decimal % 8);
}

int main() {
    int decimal;
    printf("Enter a decimal number: ");
    scanf("%d", &decimal);
    
    if (decimal == 0) {
        printf("Octal equivalent: 0\n");
    } else {
        printf("Octal equivalent: ");
        decimalToOctalRecursive(decimal);
        printf("\n");
    }
    return 0;
}
            

Output:

Enter a decimal number: 31
Octal equivalent: 37