Arabic to roman and roman to arabic

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include<string.h>

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

char romanval[1000];
char roman_Number[1000];
int i = 0;
int main()
{
	int j;
	long number;
	int x;
	printf("Enter 1 to convert an arabic number to roman or enter 2 to convert a roman number to arabic: ");
	scanf("%d", &x);

	if (x = 1)
	{
		printf("Enter a 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;
	}

if (x = 2)
{
	long int number = 0;
	printf("Enter a roman number (Valid digits are I, V, X, L, C, D, M):  \n");
	scanf("%s", roman_Number);

	while (roman_Number[i])
	{
		if (digit(roman_Number[i]) < 0)
		{
			printf("Invalid roman digit : %c", roman_Number[i]);
			return 0;
		}

		if ((strlen(roman_Number) - i) > 2)
		{
			if (digit(roman_Number[i]) < digit(roman_Number[i + 2])) {
				printf("Invalid roman number");
				return 0;
			}
		}

		if (digit(roman_Number[i]) >= digit(roman_Number[i + 1]))
			number = number + digit(roman_Number[i]);
		else {
			number = number + (digit(roman_Number[i + 1]) - digit(roman_Number[i]));
			i++;
		}
		i++;
	}

	printf("Its decimal value is : %ld", number);

	return 0;



int digit(char c) {

	int value = 0;

	switch (c) {
	case 'I': value = 1; break;
	case 'V': value = 5; break;
	case 'X': value = 10; break;
	case 'L': value = 50; break;
	case 'C': value = 100; break;
	case 'D': value = 500; break;
	case 'M': value = 1000; break;
	case '\0': value = 0; break;
	default: value = -1;
	}

	return value;
}
}