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C Program to Convert Decimal to Octal

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In this tutorial, we will learn about how to create a program in C that converts any given decimal number (by user at run-time) to its equivalent octal number. At last we have also created a user-defined function program that does the same job.

Before going through the program, if you are not aware of

then refer to Decimal to Octal conversion step by step process. Now let's move on to the program.

Decimal to Octal in C

To convert decimal number to octal number in C programming, you have to ask from user to enter the decimal number' and convert it into octal number and then display the equivalent value in octal as output like here in the program given below:

#include<stdio.h>
#include<conio.h>
int main()
{
    int decnum, octnum[50], i=0;
    printf("Enter any Decimal number: ");
    scanf("%d", &decnum);
    while(decnum != 0)
    {
        octnum[i] = decnum%8;
        i++;
        decnum = decnum/8;
    }
    printf("\nEquivalent Octal Value = ");
    for(i=(i-1); i>=0; i--)
        printf("%d", octnum[i]);
    getch();
    return 0;
}

As the above program was written under Code::Blocks IDE, therefore here is the sample run after successful build and run. This is the first snapshot of the sample run:

c program convert decimal to octal

Now supply any decimal number say 159 and press ENTER key to see its equivalent octal value as shown in the second snapshot of the sample run given here:

decimal to octal in c

Program Explained

Decimal to Octal in C without Modulous Operator

Now let's create same purpose program that is to convert any given decimal number into its equivalent octal value but without using any modulous operator as shown here in the program given below.

#include<stdio.h>
#include<conio.h>
int main()
{
    int decnum, octnum[100], i=0, temp, chck, rem;
    printf("Enter any Decimal number: ");
    scanf("%d", &decnum);
    while(decnum!=0)
    {
        temp = decnum/8;
        chck = temp*8;
        rem = decnum - chck;
        octnum[i] = rem;
        i++;
        decnum = temp;
    }
    printf("\nEquivalent Octal Value = ");
    for(i=i-1; i>=0; i--)
        printf("%d", octnum[i]);
    getch();
    return 0;
}

Here is the final snapshot of the sample run:

c decimal to octal without modulous

Program Explained

Therefore, we have successfully replaced modulous operator and created the program for same purpose but without using any modulous operator as shown in the above program.

Decimal to Octal in C using User-defined Function

Now let's create a function-driven program for same purpose. The question is, Write a program in C that converts Decimal number to Octal number using user-defined function. The answer to this question is:

#include<stdio.h>
#include<conio.h>
void DecToOct(int dec);
int octnum[50];
static int i;
int main()
{
    int decnum;
    printf("Enter any Decimal number: ");
    scanf("%d", &decnum);
    DecToOct(decnum);
    printf("\nEquivalent Octal Value = ");
    for(i=(i-1); i>=0; i--)
        printf("%d", octnum[i]);
    getch();
}
void DecToOct(int dec)
{
    while(dec != 0)
    {
        octnum[i] = dec%8;
        i++;
        dec = dec/8;
    }
}

Here is the final snapshot of sample run of above program:

c decimal to octal using function

Here we have declared the variable i as static variable. Because static variable remembers its previous value. And we have not initialized the value of i with 0, because static variable holds 0 as its initial value. That is if you will not initialize any value to any static variable, therefore 0 gets automatically initialized to it. We have created the array octnum[] and the variable i outside the main() function so that both the array and variable stays known throughout the program, that is inside both the function namely, main() and DecToOct().

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