# C Program to Convert Hexadecimal to Octal

In this article, you will learn and get code about the conversion of a number given by user (at run-time) from hexadecimal to octal.

Before going to the program, if you are not aware of:

• Octal Number
• Hexadecimal to Octal Conversion

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

## Hexadecimal to Octal in C

To convert hexadecimal number to octal number in C programming, you have to ask from user to enter the hexadecimal number and then convert it into its equivalent octal value. And then display the equivalent value in octal as shown in the program given below.

Note - There is no any direct conversion from hexadecimal to octal. Therefore you can prefer either hexadecimal to decimal and then decimal to octal, or hexadecimal to binary and then binary to octal.

Let's create a program that converts hexadecimal to binary and then binary to octal. Later on, the same program is also created with second way. In my opinion, then second way is easier to create or understand.

```#include<stdio.h>
#include<conio.h>
#include<string.h>
int main()
{
int i=0, chk=0, len, rem, binDigit, octalDigit;
long long binaryInt=0, temp=1, octalNum, binaryNum;
char hexdec, binnum="";
printf("Enter Hexadecimal Number: ");
gets(hexdec);
while(hexdec[i])
{
switch(hexdec[i])
{
case '0':
strcat(binnum, "0000");
break;
case '1':
strcat(binnum, "0001");
break;
case '2':
strcat(binnum, "0010");
break;
case '3':
strcat(binnum, "0011");
break;
case '4':
strcat(binnum, "0100");
break;
case '5':
strcat(binnum, "0101");
break;
case '6':
strcat(binnum, "0110");
break;
case '7':
strcat(binnum, "0111");
break;
case '8':
strcat(binnum, "1000");
break;
case '9':
strcat(binnum, "1001");
break;
case 'A':
strcat(binnum, "1010");
break;
case 'a':
strcat(binnum, "1010");
break;
case 'B':
strcat(binnum, "1011");
break;
case 'b':
strcat(binnum, "1011");
break;
case 'C':
strcat(binnum, "1100");
break;
case 'c':
strcat(binnum, "1100");
break;
case 'D':
strcat(binnum, "1101");
break;
case 'd':
strcat(binnum, "1101");
break;
case 'E':
strcat(binnum, "1110");
break;
case 'e':
strcat(binnum, "1110");
break;
case 'F':
strcat(binnum, "1111");
break;
case 'f':
strcat(binnum, "1111");
break;
default:
chk = 1;
break;
}
i++;
}
if(chk==0)
{
len = strlen(binnum);
while(len!=0)
{
if(binnum[len-1]=='0')
binDigit=0;
else
binDigit=1;
binaryInt = binaryInt + (binDigit*temp);
temp = temp*10;
len--;
}
binaryNum = binaryInt;
octalNum = 0;
temp = 1;
while(binaryNum>0)
{
rem = binaryNum%1000;
switch(rem)
{
case 0:
octalDigit = 0;
break;
case 1:
octalDigit = 1;
break;
case 10:
octalDigit = 2;
break;
case 11:
octalDigit = 3;
break;
case 100:
octalDigit = 4;
break;
case 101:
octalDigit = 5;
break;
case 110:
octalDigit = 6;
break;
case 111:
octalDigit = 7;
break;
}
octalNum = (octalDigit*temp) + octalNum;
binaryNum = binaryNum/1000;
temp = temp*10;
}
printf("\nEquivalent Octal Value = %lld", octalNum);
}
else
getch();
return 0;
}```

This program was compiled and executed using Code::Blocks IDE. Here is the sample run. This is the first snapshot of sample run:

Now supply any input value (as hexadecimal number) say 4CA and press ENTER key to see its equivalent value in octal number system as shown in the second snapshot given below:

In above program we have converted the hexadecimal value to its equivalent binary value. To learn more about it, refer to Hexadecimal to Binary in C tutorial.

After performing this conversion, we have applied the code given below:

```len = strlen(binnum);
while(len!=0)
{
if(binnum[len-1]=='0')
binDigit=0;
else
binDigit=1;
binaryInt = binaryInt + (binDigit*temp);
temp = temp*10;
len--;
}```

to convert the binary value stored in character array to integer form. Then applied the conversion from binary to octal. You can also refer to Binary to Octal in C tutorial to modify the code given above with your choice.

### Hexadecimal to Octal in C using Indirect Conversion

This program converts given hexadecimal number (by user at run-time) into its decimal equivalent. And then the decimal equivalent gets converted into its octal equivalent.

```#include<stdio.h>
#include<conio.h>
#include<math.h>
int main()
{
int decnum=0, rem, i=0, len=0, octnum;
char hexnum;
printf("Enter any Hexadecimal Number: ");
scanf("%s", hexnum);
while(hexnum[i]!='\0')
{
len++;
i++;
}
len--;
i=0;
while(len>=0)
{
rem = hexnum[len];
if(rem>=48 && rem<=57)
rem = rem-48;
else if(rem>=65 && rem<=70)
rem = rem-55;
else if(rem>=97 && rem<=102)
rem = rem-87;
else
{
printf("\nYou've entered an invalid Hexadecimal digit");
getch();
return 0;
}
decnum = decnum + (rem*pow(16, i));
len--;
i++;
}
i=0;
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;
}```

For in-depth learning of above code, you can follow the separate program on hexadecimal to decimal and decimal to octal.

#### Same Program in Other Languages

C Online Test

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