# C++ Program to Convert Octal to Hexadecimal

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In this article, you will learn and get code on octal to hexadecimal conversion in C++. The program is created with and without using user-defined function.

Before going through program, if you are not aware about formula or steps used for the conversion of octal to hexadecimal, you can refer to octal to hexadecimal steps to get everything that is required while the conversion from octal to hexadecimal.

## Octal to Hexadecimal without Function

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

```#include<iostream>
#include<string.h>
using namespace std;
int main()
{
int octalNum, rev=0, rem, chk=0, hex=0, mul=1, i=0, k=0;
char binaryNum = "", hexnum;
cout<<"Enter any Octal Number: ";
cin>>octalNum;
while(octalNum!=0)
{
rem = octalNum%10;
if(rem>7)
{
chk++;
break;
}
rev = (rev*10) + rem;
octalNum = octalNum/10;
}
if(chk==0)
{
octalNum = rev;
while(octalNum!=0)
{
rem = octalNum%10;
switch(rem)
{
case 0: strcat(binaryNum, "000");
break;
case 1: strcat(binaryNum, "001");
break;
case 2: strcat(binaryNum, "010");
break;
case 3: strcat(binaryNum, "011");
break;
case 4: strcat(binaryNum, "100");
break;
case 5: strcat(binaryNum, "101");
break;
case 6: strcat(binaryNum, "110");
break;
case 7: strcat(binaryNum, "111");
break;
}
octalNum = octalNum/10;
}
while(binaryNum[k]!='\0')
k++;
chk=1;
k--;
while(k>=0)
{
if(binaryNum[k]=='0')
rem = 0;
else
rem = 1;
hex = hex + (rem*mul);
if(chk%4==0)
{
if(hex<10)
hexnum[i] = hex+48;
else
hexnum[i] = hex+55;
mul = 1;
hex = 0;
chk = 1;
i++;
}
else
{
mul = mul*2;
chk++;
}
k--;
}
if(chk!=1)
hexnum[i] = hex+48;
if(chk==1)
i--;
chk = 0;
for(i=i; i>=0; i--)
{
if(hexnum[i]=='0' && chk==0)
{
chk++;
continue;
}
else
cout<<hexnum[i];
}
}
else
cout<<"\nInvalid Octal Digit "<<rem;
cout<<endl;
return 0;
}```

This program was build and run under Code::Blocks IDE. Here is its sample run:

Now input any octal number say 377 and press `ENTER` key to see its equivalent hexadecimal value as shown in the output given below:

This program converts octal to binary, and then binary to hexadecimal

You can also approach the second way, that is octal to decimal and then decimal to hexadecimal. Here the first way is used, because the second way is little easier to create and understand. So you can follow both the article and create it with yourself.

## Octal to Hexadecimal using Function

This program does the same job as of previous program. The only difference is, it is created using user-defined function octalToHexa().

```#include<iostream>
#include<string.h>
int reverseNum(int);
void octalToHexa(int);
static int chk, i;
char hexnum;
using namespace std;
int main()
{
int octalNum;
cout<<"Enter any Octal Number: ";
cin>>octalNum;
octalToHexa(octalNum);
if(chk!=0)
{
chk = 0;
for(i=i; i>=0; i--)
{
if(hexnum[i]=='0' && chk==0)
{
chk++;
continue;
}
else
cout<<hexnum[i];
}
}
else
cout<<"\nInvalid Octal Digit!";
cout<<endl;
return 0;
}
void octalToHexa(int octalNum)
{
int rev=0, rem, hex=0, mul=1, k=0;
char binnum = "";
rev = reverseNum(octalNum);
if(rev!=0)
{
octalNum = rev;
while(octalNum!=0)
{
rem = octalNum%10;
switch(rem)
{
case 0: strcat(binnum, "000");
break;
case 1: strcat(binnum, "001");
break;
case 2: strcat(binnum, "010");
break;
case 3: strcat(binnum, "011");
break;
case 4: strcat(binnum, "100");
break;
case 5: strcat(binnum, "101");
break;
case 6: strcat(binnum, "110");
break;
case 7: strcat(binnum, "111");
break;
}
octalNum = octalNum/10;
}
while(binnum[k]!='\0')
k++;
chk=1;
k--;
while(k>=0)
{
if(binnum[k]=='0')
rem = 0;
else
rem = 1;
hex = hex + (rem*mul);
if(chk%4==0)
{
if(hex<10)
hexnum[i] = hex+48;
else
hexnum[i] = hex+55;
mul = 1;
hex = 0;
chk = 1;
i++;
}
else
{
mul = mul*2;
chk++;
}
k--;
}
if(chk!=1)
hexnum[i] = hex+48;
if(chk==1)
i--;
}
else
chk=0;
}
int reverseNum(int octalNum)
{
int rem, rev=0;
while(octalNum!=0)
{
rem = octalNum%10;
if(rem>7)
return 0;
rev = (rev*10) + rem;
octalNum = octalNum/10;
}
return rev;
}```

It produces the same output as of previous program.

#### Same Program in Other Languages

C++ Online Test

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