C program to convert Decimal to Hexadecimal

In this blog post, we will see the C program to convert Decimal to Hexadecimal. In the interview, people ask the below questions,

How will you convert decimal to hexadecimal value?
Write a C program to convert decimal number system value to hexadecimal number system?
Implement logic to convert a decimal number to a hexadecimal number system?
Get a decimal number from the user and convert it to its hexadecimal equivalent?
How do you convert the number with base value 10 to base value 16?

Before writing the code let’s understand what hexadecimal and decimal are.

The hexadecimal number system is a base 16 number system. The hexadecimal number is represented by 16 values i.e 0 1 2 3 4 5 6 7 8 9 A B C D E F.

The decimal number system is a base 10 number system. It uses 10 symbols to represent all numbers i.e. 0123456789

Conversion steps from decimal to hex:

Divide the number by 16.
Get the integer quotient for the next iteration.
Get the remainder for the hex digit.
Repeat the steps until the quotient is equal to 0.

Example,

Convert 6711₁₀ to hex:

Division by 16	Quotient (integer)	Remainder (decimal)	Remainder (hex)	Digit #
6711/16	419	7	7	0
419/16	26	3	3	1
26/16	1	10	A	2
1/16	0	1	1	3

Decimal to hexadecimal conversion table:

The following table shows 0-16 decimal numbers with the corresponding hexadecimal numbers.

Decimalbase 10	Hexbase 16
0	0
1	1
2	2
3	3
4	4
5	5
6	6
7	7
8	8
9	9
10	A
11	B
12	C
13	D
14	E
15	F
16	10

C Program to convert a decimal number to a hexadecimal number:

The following are C programs to convert a decimal number to a hexadecimal number.

Method 1:

// C program to convert a decimal
//

#include <stdio.h>

// function to convert decimal to hexadecimal
void decToHex(int decNum)
{
    // char array to store hexadecimal number
    char hexaDeciNum[50];

    // counter for hexadecimal number array
    int i = 0;
    while (decNum != 0)
    {
        /* temporary variable to
        store right most digit*/
        int temp = 0;

        // Get the right most digit
        temp = decNum % 16;

        // check if temp < 10
        if (temp < 10)
        {
            hexaDeciNum[i] = temp + 48;
            i++;
        }
        else
        {
            hexaDeciNum[i] = temp + 55;
            i++;
        }

        decNum = decNum / 16; // get the quotient
    }

    printf("0x"); //print hex symbol

    // printing hexadecimal number array in reverse order
    for (int j = i - 1; j >= 0; j--)
    {
        printf("%c", hexaDeciNum[j]);
    }
}

int main()
{
    int decNum;
    
    printf("Enter a decimal number: ");
    scanf("%d", &decNum);
    
    decToHex(decNum);

    return 0;
}

Output:

How it works:

Step 1: Calculate remainder when 6711 is divided by 16 is 7. Therefore, temp = 7. As temp is less than 10. So, hexaDeciNum[0] = 48 + 7= 55 = ‘7’.

Step 2: Divide 6711 by 16. New number is 6711/16 = 419.

Step 3: Calculate remainder when 419 is divided by 16 is 3. Therefore, temp = 3. As temp is less than 10. So, hexaDeciNum[0] = 48 + 3= 51= ‘3’.

Step 4: Divide 419 by 16. New number is 419 /16 = 26.

Step 5: Calculate remainder when 26 is divided by 16 is 10. Therefore, temp = 10. As temp is greater than 10. So, hexaDeciNum[0] = 55 + 10= 65= ‘A’.

Step 6: Divide 26 by 16. New number is 26/16 = 1.

Step 7: Calculate remainder when 1 is divided by 16 is 1. Therefore, temp = 1. As temp is less than 10. So, hexaDeciNum[0] = 48 + 1= 49 = ‘1’.

Step 8: Divide 1 by 16. New number is 1/16 = 10.

Step 9: Now number becomes = 0, so iterating loops will break and print hexaDeciNum array reverse order.

Method-2:

The steps are the almost same as the above method. Here I have used the ternary operator in place of the if-else statement.

#include <stdio.h>

//function to convert decimal to hexadecimal
void decToHex(int decNum)
{
    // char array to store hexadecimal number
    char hexaDeciNum[50];

    // counter for hexadecimal number array
    int i = 0;

    while (decNum != 0)
    {
        /* temporary variable to
        store right most digit*/
        int temp = decNum % 16;

        // check if temp < 10
        hexaDeciNum[i++] = temp + ((temp < 10) ? 48 :55);

        decNum = decNum / 16; // get the quotient
    }
    printf("0x"); //print hex symbol

    // printing hexadecimal number array in reverse order
    for (int j = i - 1; j >= 0; j--)
    {
        printf("%c", hexaDeciNum[j]);
    }
}
int main()
{
    int decNum;

    printf("Enter a decimal number: ");
    scanf("%d", &decNum);

    decToHex(decNum);
    
    return 0;
}

Method-3:

Using the literal string you can also convert decimal to hex.

// C program to convert a decimal

#include <stdio.h>

// function to convert decimal to hexadecimal
void decToHex(int decNum)
{
    // char array to store hexadecimal number
    char hexaDeciNum[50];
    int i = 0;

    while (decNum != 0)
    {
        hexaDeciNum[i] = (char)(*("0123456789ABCDEF"
                                  + ((decNum % 16) & (15))));
        decNum = (decNum / 16);
        ++i;
    }

    printf("0x"); //print hex symbol

    // printing hexadecimal number array in reverse order
    for (int j = i - 1; j >= 0; j--)
    {
        printf("%c", hexaDeciNum[j]);
    }
}

int main()
{
    int decNum;

    printf("Enter a decimal number: ");
    scanf("%d", &decNum);

    decToHex(decNum);

    return 0;
}