C Program on Decimal to Hexadecimal Number Conversion

Question:

Algorithm:

Explanation:

Decimal to hexadecimal conversion is based on repeated division by 16. Since hexadecimal has base 16, each division gives one hexadecimal digit as a remainder. If the remainder is between 0 and 9, the same digit is used. If the remainder is 10, 11, 12, 13, 14 or 15, the corresponding hexadecimal digit is A, B, C, D, E or F. To make this conversion simple, the program stores all sixteen possible hexadecimal symbols in the character array dig.

The program first reads the decimal number. A special check is made for 0 because the loop while(deci > 0) will not run when the input is 0. In that case, the hexadecimal form is also 0, so the program prints the answer directly. For any positive number, the program repeatedly finds the remainder after division by 16. That remainder is used as an index in the dig array, and the selected hexadecimal character is stored in the hex array.

The remainders are produced from right to left. For example, decimal 47 first gives remainder 15, which is F, and then gives remainder 2. The correct hexadecimal result is 2F, not F2. Therefore, after collecting all digits, the program prints the hex array backwards. This avoids the non-standard strrev() function and keeps the program portable across standard C compilers.

C Program:

/*
 * C Program to convert a Decimal number into a Hexadecimal number
 * @author : www.guideforschool.com
 * @Program Type : C Program
 */

#include <stdio.h>

int main(void)
{
    int deci, i = 0, j, rem;
    char hex[100]; // Array for storing hexadecimal digits.
    char dig[] = {'0', '1', '2', '3', '4', '5', '6', '7',
                  '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};

    printf("\nEnter a decimal number : ");
    scanf("%d", &deci);

    if(deci == 0)
    {
        printf("\nEquivalent Hexadecimal number = 0");
        return 0;
    }

    while(deci > 0)
    {
        rem = deci % 16;
        hex[i++] = dig[rem]; // Store digit according to the remainder.
        deci = deci / 16;
    }

    printf("\nEquivalent Hexadecimal number = ");

    // Print the stored digits in reverse order.
    for(j = i - 1; j >= 0; j--)
    {
        printf("%c", hex[j]);
    }

    return 0;
}

Output:

Enter a decimal number : 47
Equivalent Hexadecimal number = 2F

Enter a decimal number : 1243
Equivalent Hexadecimal number = 4DB