programming-examples/c/_Basic/C Program to Convert Numbers to Roman Numerals.c

/*
 * C Program to Convert Numbers to Roman Numerals
 */
#include <stdio.h>

void predigit(char num1, char num2);
void postdigit(char c, int n);

char romanval[1000];
int i = 0;
int main()
{
    int j;
    long number;
    printf("Enter the number: ");
    scanf("%d", &number);
    if (number <= 0)
        {
            printf("Invalid number");
            return 0;
        }
    while (number != 0)
        {
            if (number >= 1000)
                {
                    postdigit('M', number / 1000);
                    number = number - (number / 1000) * 1000;
                }
            else if (number >= 500)
                {
                    if (number < (500 + 4 * 100))
                        {
                            postdigit('D', number / 500);
                            number = number - (number / 500) * 500;
                        }
                    else
                        {
                            predigit('C','M');
                            number = number - (1000-100);
                        }
                }
            else if (number >= 100)
                {
                    if (number < (100 + 3 * 100))
                        {
                            postdigit('C', number / 100);
                            number = number - (number / 100) * 100;
                        }
                    else
                        {
                            predigit('L', 'D');
                            number = number - (500 - 100);
                        }
                }
            else if (number >= 50 )
                {
                    if (number < (50 + 4 * 10))
                        {
                            postdigit('L', number / 50);
                            number = number - (number / 50) * 50;
                        }
                    else
                        {
                            predigit('X','C');
                            number = number - (100-10);
                        }
                }
            else if (number >= 10)
                {
                    if (number < (10 + 3 * 10))
                        {
                            postdigit('X', number / 10);
                            number = number - (number / 10) * 10;
                        }
                    else
                        {
                            predigit('X','L');
                            number = number - (50 - 10);
                        }
                }
            else if (number >= 5)
                {
                    if (number < (5 + 4 * 1))
                        {
                            postdigit('V', number / 5);
                            number = number - (number / 5) * 5;
                        }
                    else
                        {
                            predigit('I', 'X');
                            number = number - (10 - 1);
                        }
                }
            else if (number >= 1)
                {
                    if (number < 4)
                        {
                            postdigit('I', number / 1);
                            number = number - (number / 1) * 1;
                        }
                    else
                        {
                            predigit('I', 'V');
                            number = number - (5 - 1);
                        }
                }
        }
    printf("Roman number is: ");
    for(j = 0; j < i; j++)
        printf("%c", romanval[j]);
    return 0;
}

void predigit(char num1, char num2)
{
    romanval[i++] = num1;
    romanval[i++] = num2;
}

void postdigit(char c, int n)
{
    int j;
    for (j = 0; j < n; j++)
        romanval[i++] = c;
}