Simple string issue

[LiverpoolFTW]

So the assignment is to take a string the user inputs and reverse each word within the string (not to reverse the string itself, just each word individually).

example:
Enter your line of string: I am going to reverse the string
Your reversed string is : I ma gniog ot esrever eht gnirts

I am having issues with my code however. I have checked my for loops over and over and they shoudl theoretically work but i think my main problem is i dont know exactly how to check the str.find() if it does not find the value. I want to say, if you dont find a space in the string then output the string reversed_string and end the program. Any constructive criticism is welcome. Thanks in advance.

EDIT: Right now the program just allows the user to input their string and then ends. I have checked and it enters the while loop fine and finds the position of the first space just fine but it never gets to the next space or aything.

EDIT: I did make some progress. now it spits out something for the reversed_string but still not correct. code has been updated.

EDIT: Got it :). updated code for future references.

#include <iostream>
#include <string>
using namespace std;

//A space has been found, the word between that space and the previous space must be reversed
void reverse_word (string &original_string_par, string &reversed_string_par, int space_position_par, int previous_space_position_par);
//The word has been reversed and added to the new string

int main ()
{
	string original_string, reversed_string;
	string s1 (" ");	
	int previous_space_position = 0, x = 0, space_position = 0;

	cout << "Enter a string: ";
	//Get the entire string the user has inputed
	getline(cin, original_string);
	//For the length of the string, do the following.
	while (x < original_string.length())
	{
		//Check each value of the string and see if it is a space. if not then continue to next value.
		// if it is then mark that position as space_position and reverse the word that is between that and the previous_space_position.
		if (original_string.at(x) == ' ')
		{
			space_position = x;
			reverse_word (original_string, reversed_string, space_position, previous_space_position);
			//After a word has been reversed, the previous space position must be updated.
			previous_space_position = space_position;
		}

		x++;
	}
	
	//The previous loop does not catch the last word unless the last value is a space. so this will reverse the last word of the string.
	space_position = original_string.length();
	reverse_word (original_string, reversed_string, space_position, previous_space_position);
	cout << "Your reversed string is: " << reversed_string << endl;
	
	return 0;
}
	
void reverse_word (string &original_string_par, string &reversed_string_par, int space_position_par, int previous_space_position_par)
{
	//A special case must be made for the first space found as the first value is a letter and not a space. precious_space_position = 0 which is the position of a lettter.
	if (previous_space_position_par == 0)
	{
		int x = 2;
		reversed_string_par += original_string_par[space_position_par-1];

		for (int i = 1; i < space_position_par; i++)
		{
			reversed_string_par += original_string_par[space_position_par - x];
			x++;
		}
	}
	
	//For all other cases take the letter right before the space found and add it to the string. got closer and closer to the previous_space_position until the starting letter is reached.
	else
	{
		for (int i = space_position_par; i > previous_space_position_par; i--)
		{
			reversed_string_par += original_string_par[i - 1];
		}
	}
	
	reversed_string_par += ' ';
	
}