C++ Program to Convert Decimal to Hexadecimal

In this article, you will learn and get code on decimal to hexadecimal conversion in C++. The decimal to hexadecimal conversion program in C++ is created here using following approaches:

• Decimal to Hexadecimal without using Function
• Using user-defined Function

But before going through these programs, if you are not aware about some simple steps used for the conversion, then you can refer to decimal to hexadecimal to get every required things.

Decimal to Hexadecimal in C++

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

The question is, write a program in C++ to receive decimal number and print its equivalent value in hexadecimal. The answer to this question is given below:

#include<iostream>
using namespace std;
int main()
{
    int decimalNum, rem, i=0;
    char hexaDecimalNum[50];
    cout<<"Enter the Decimal Number: ";
    cin>>decimalNum;
    while(decimalNum!=0)
    {
        rem = decimalNum%16;
        if(rem<10)
            rem = rem+48;
        else
            rem = rem+55;
        hexaDecimalNum[i] = rem;
        i++;
        decimalNum = decimalNum/16;
    }
    cout<<"\nEquivalent Hexadecimal Value: ";
    for(i=i-1; i>=0; i--)
        cout<<hexaDecimalNum[i];
    cout<<endl;
    return 0;
}

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

Now enter the input say 259 (decimal number) and press ENTER key to convert and print its equivalent value in hexadecimal as shown in the snapshot given below:

The dry run of above program with user input 259 (decimal number), goes like:

• Initial value, i=0
• When user enters the decimal number input say 259, then it gets stored in decimalNum variable. So decimalNum=259
• Now the condition of while loop gets evaluated.
• That is, the condition decimalNum!=0 or 259!=0 evaluates to be true, therefore program flow goes inside the loop
• decimalNum%16 or 259%16 or 3 gets initialized to rem. So rem=3
• Now the condition rem<10 or 3<10 evaluates to be true, therefore program flow goes inside the if's body and the statement
  rem = rem+48;
  gets evaluated
• That is, rem+48 or 3+48 or 51 gets initialized to rem. So rem=51
• Because, the condition of if evaluates to be true, therefore else's body gets skipped
• Now the value of rem (51) gets initialized to hexaDecimalNum[i] or hexaDecimalNum[0]
• The value of i gets incremented. Now i=1
• And then decimalNum/16 or 259/16 or 16 gets initialized to decimalNum. So decimalNum=16
• Now program flow goes back and evaluates the condition of while loop again with new value of decimalNum (16)
• Again the condition evaluates to be true, therefore program flow again goes inside the loop
• decimalNum%16 or 16%16 or 0 gets initialized to rem
• Again the condition of if, that is, rem<10 or 0<10 evaluates to be true again, therefore rem+48 or 0+48 or 48 gets initialized to rem. Now rem=0
• And rem or 0 gets initialized to hexaDecimalNum[i] or hexaDecimalNum[1]. So hexaDecimalNum[1]=0
• Again the value of i gets incremented. So i=2
• decimalNum/16 or 1 gets initialized to decimalNum
• Continue the process until the condition of while loop evaluates to be false
• On continuing the process, we'll get the value of rem as 51, 48, 49 that gets initialized to hexaDecimalNum[0], hexaDecimalNum[1], and hexaDecimalNum[2]
• Print the value of hexaDecimalNum[] from its last to 0^th index
• Because 51, 48, 49 are ASCII values of 3, 0, 1. Therefore in reverse order, 103 gets printed using for loop. That is the equivalent hexadecial value of given decimal number (that was 259)

Note - If the value of rem (remainder) will be greater than or equal to 10, then equivalent hexadecimal alphabet's ASCII value gets assigned (A-F). That is, A for 10, B for 11, C for 12 and so on.

Convert Decimal to Hexadecimal from 1 to 20

This program converts all the decimal number from 1 to 20 into its equivalent hexadecial value without asking for user input:

#include<iostream>
using namespace std;
int main()
{
    int decimalNum, rem, i, k;
    char hexaDecimalNum[50];
    cout<<"Decimal Number\tHexadecimal Number\n";
    for(k=1; k<=20; k++)
    {
        decimalNum=k;
        i=0;
        while(decimalNum!=0)
        {
            rem = decimalNum%16;
            if(rem<10)
                rem = rem+48;
            else
                rem = rem+55;
            hexaDecimalNum[i] = rem;
            i++;
            decimalNum = decimalNum/16;
        }
        cout<<k<<"\t\t";
        for(i=i-1; i>=0; i--)
            cout<<hexaDecimalNum[i];
        cout<<endl;
    }
    return 0;
}

Here is its sample output:

Decimal to Hexadecimal using Function

Let's create the same purpose program using user-defined function DecToHexDec(). This function converts decimal number to hexadecimal.

#include<iostream>
using namespace std;
int DecToHexDec(int dec, int);
char hexaDecNum[50];
int main()
{
    int decimalNum, i;
    cout<<"Enter the Decimal Number: ";
    cin>>decimalNum;
    i = DecToHexDec(decimalNum, 0);
    cout<<"\nEquivalent Hexadecimal Value: ";
    for(i=i-1; i>=0; i--)
        cout<<hexaDecNum[i];
    cout<<endl;
    return 0;
}
int DecToHexDec(int dec, int i)
{
    int rem;
    while(dec!=0)
    {
        rem = dec%16;
        if(rem<10)
            rem = rem+48;
        else
            rem = rem+55;
        hexaDecNum[i] = rem;
        i++;
        dec = dec/16;
    }
    return i;
}

Here is its sample run with user input 364 as decimal number input:

Same Program in Other Languages

• C Decimal to Hexadecimal Conversion
• Java Decimal to Hexadecimal Conversion
• Python Decimal to Hexadecimal Conversion

C++ Online Test