C Program to Convert Decimal to Hexadecimal

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) into its equivalent hexadecimal value. We have also created a user-defined function that does the same job of converting decimal number to hexadecimal number.

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

• Decimal Number
• Hexadecimal Number
• Decimal to Hexadecimal Conversion Process

Then refer to, Decimal to Hexadecimal conversion step by step process. Let's move on to the program.

Decimal to Hexadecimal in C

To convert decimal number to hexadecimal number in C programming, you have to ask from user to enter the decimal number as input and then convert it into its equivalent hexadecimal value as shown in the program given below. The question is, Write a program in C that converts Decimal to Hexadecimal. Here is its answer.

#include<stdio.h>
#include<conio.h>
int main()
{
    int decnum, rem, i=0;
    char hexnum[50];
    printf("Enter any decimal number: ");
    scanf("%d", &decnum);
    while(decnum!=0)
    {
        rem = decnum%16;
        if(rem<10)
            rem = rem+48;
        else
            rem = rem+55;
        hexnum[i] = rem;
        i++;
        decnum = decnum/16;
    }
    printf("\nEquivalent Value in Hexadecimal = ");
    for(i=i-1; i>=0; i--)
        printf("%c", hexnum[i]);
    getch();
    return 0;
}

As the above program was build and run under Code::Blocks IDE, therefore after successful build and run, you will get the following output. This is the first snapshot of the sample run:

Now supply any decimal number as input say 172 and press ENTER key to see the equivalent hexadecimal value as output. Here is the second snapshot of the sample run:

Here is another sample run. This is the final snapshot of the sample run:

Program Explained

• Receive any decimal number by user
• Create a while loop with condition decnum!=0. Here decnum variable holds the decimal number value entered by user at run-time
• Let's suppose that user has entered 172 as input
• Therefore at first run of the while loop, the condition decnum!=0 or 172!=0 evaluates to be true. Therefore program flow goes inside the loop
• And decnum%16 or 172%16 (we will get a remainder as 12 because while dividing the number 172 (dividend) with 16 (divisor), we will get 10 as quotient and 12 as remainder) or 12 gets initialized to rem variable
• Now using if statement check whether the value inside rem is less than 10 or not, because if value is less than 10, then the value may be from 0, 1, 2, ..., 8, 9. And we all knows that the ASCII code for 0, 1, 2, ..., 8, 9 are 48, 49, 50, ..., 56, 57. Therefore we have to apply the addition with 48 to the value present inside rem variable
• Because if rem is 0, then rem+48 or 0+48 or 48 gets initialized to rem (which is the ASCII code for 0). Or if rem holds the value 4, then rem+48 or 4+48 or 52 gets initialized to rem that equals the ASCII code for 4
• And finally rem (ASCII code value) gets initialized to hexnum[i] (i holds 0 as its initial value) or hexnum[0]
• The second case is, if value of rem is not less than 10, therefore value inside the rem variable may be from 10, 11, 12, ..., 14, 15
• In hexadecimal number system, 10 is represented by A, 11 is represented by B, ..., 15 is represented by F. And ASCII code for A, B, C, ..., E, F are 65, 66, 67, ..., 69, 70
• Therefore, rem+55 gets initialized to rem. We have added the value of rem with 55 as if value of rem is 10, then we have to initialize ASCII code of A, as 10 is repsented by A. And the ASCII code of A is 65. In this way the ASCII code of 0, 1, 2, ..., E, or F gets initialized to hexnum[i] or hexnum[0]. Therefore, at first run of the while loop. We have got a remainder value as 12, therefore rem+55 or 12+55 or 67 gets initialized to rem and then rem gets initialized to hexnum[i] or hexnum[0]
• Then value of i gets incremented and becomes 1. And decnum/16 or 172/16 or 10 gets initialized to decnum
• Now at second run of the while loop, the condition decnum!=0 or 10!=0 evaluates to be true, therefore program flow goes inside the loop again and do the similar operation as told in above steps
• After exiting from the while loop, we have successfully stored the equivalent hexadecimal value of given decimal number one by one
• Therefore to print the number in hexadecimal form, we have to create a for loop, that runs from one less than the current value of i to 0
• Because at last run, we have incremented the value of i. Here last run means decnum contains 0, therefore the condition (decnum!=0 or 0!=0) evaluates to be false . Therefore we have to subtract the current value of i with 1
• Print all the digit of hexnum[] array one by one from last digit to first digit
• In this way, we have successfully printed equivalent hexadecimal value of given decimal value by user at run-time

Decimal to Hexadecimal in C without Modulous Operator

Now let's create the same program but without using any modulous operator. That is we have to find out the remainder without using modulous operator. Therefore to find out remainder, we have divided the number present inside decnum by 16, and stored its quotient value inside a variable say temp, then again multiply the quotient value with 16 and stored the multiplication result to a variable say chck. Now subtract chck from decnum (decnum - chck) and initialized it to rem variable, that will holds the current remainder.

For example, if user has supplied 172 as input, therefore at first run decnum/16 or 10 gets initialized to temp Then temp*16 or 10*16 or 160 gets initialized to chck. Now decnum-chck or 172-160 or 12 gets initialized to rem which is the remainder this time. In this way, we have replaced the modulous operator with three line of code as shown in the program given below:

#include<stdio.h>
#include<conio.h>
int main()
{
    int decnum, hexnum[50], temp, chck, i=0, rem;
    printf("Enter any Decimal number: ");
    scanf("%d", &decnum);
    while(decnum!=0)
    {
        temp = decnum/16;
        chck = temp*16;
        rem = decnum - chck;
        if(rem<10)
            rem = rem+48;
        else
            rem = rem+55;
        hexnum[i] = rem;
        i++;
        decnum = temp;
    }
    printf("\nEquivalent Hexadecimal Value = ");
    for(i=i-1; i>=0; i--)
        printf("%c", hexnum[i]);
    getch();
    return 0;
}

Here is the final snapshot of the sample run:

Decimal to Hexadecimal in C using User-defined Function

Now let's create a user-defined function named DecToHex() that takes one argument (the decimal number entered by user). Here we have declared the variable i and the array hex[] outside both the function say main() and DecToHex() to make it known for both the function. Here the variable i is declared as static variable because static variable remembers its previous value. One last thing is, we have not initialized the static variable i with 0 (which is required), because by default static variable holds 0 as its initial value after declaring the static variable. Rest of the thing is similar that can easily be understand by you.

#include<stdio.h>
#include<conio.h>
void DecToHex(int dec);
static int i;
char hex[50];
int main()
{
    int decnum;
    printf("Enter any decimal number: ");
    scanf("%d", &decnum);
    DecToHex(decnum);
    printf("\nEquivalent Value in Hexadecimal = ");
    for(i=i-1; i>=0; i--)
        printf("%c", hex[i]);
    getch();
    return 0;
}
void DecToHex(int dec)
{
    int rem;
    while(dec!=0)
    {
        rem = dec%16;
        if(rem<10)
            rem = rem+48;
        else
            rem = rem+55;
        hex[i] = rem;
        i++;
        dec = dec/16;
    }
}

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

Same Program in Other Languages

• C++ Decimal to Hexadecimal
• Java Decimal to Hexadecimal
• Python Decimal to Hexadecimal

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