Symmetric Relation

[hunterx893]

Hi, I made a function that looks through a vector and looks through the pair of elements. Example: vector = {1 1 2 2 2 3 3 2} but actually its in pairs (1,1),(2,2),(2,3)(3,2). According to the Symmetric definition if 'A' is related to 'B' then 'B' is related to 'A'. From the vector it is symmetric since in the set there is (2,3) and (3,2). So far this is my code that checks to see if symmetric.

#include <vector>

using namespace std; 

const int MAX = 100;

void putinArray(vector <int> & orderedpairs, int arr[MAX][MAX], int dom, int rang); 
bool RelationOrFunction(int arr[MAX][MAX], int dom, int rang);
int SurOrInj(int arr[MAX][MAX], int dom, int rang); 
bool Reflexive(vector <int> pairs, int dom);
bool Symmetric(vector <int> pairs);
void printArray(int arr[MAX][MAX], int dom, int rang);

int main()
{
	int testcase, domain, range, pairs, p;
	int i = 0; 
	int j = 0;
	vector <int> nums;
	int arr[MAX][MAX] = {{0}}; 
	
	cout << "Please input the amount of test cases: "; 
	cin >> testcase; 
	cout << endl; 

	while(i < testcase)
	{
		cout << "Please type the amount of ordered pairs: "; 
		cin >> pairs; 
		cout << endl; 

		cout << "Please type the range of the domain: "; 
		cin >> domain; 
		cout << endl;

		cout << "Please type the range of the range: "; 
		cin >> range; 
		cout << endl;

		cout << "Please type the pairs: " ; 
		while(j < (pairs * 2))
		{
			cin >> p; 
			nums.push_back(p);
			j++;
		}
		putinArray(nums,arr,domain,range);
		printArray(arr,domain,range);		
		
		if(RelationOrFunction(arr,domain,range))
		{
			cout << "Function "; 
			if(SurOrInj(arr,domain,range) == 1)
			{
				cout << "Injective "; 
			}
			else if(SurOrInj(arr,domain,range) == 2)
			{
				cout << "Surjective "; 
			}
			else if(SurOrInj(arr,domain,range) == 3)
			{
				cout << "Injective Surjective Bijective "; 
			}
			else if(SurOrInj(arr,domain,range) ==4)
			{
				cout << " "; 
			}
		}
		else 
		{
			cout << "Relation "; 
			
			if(Reflexive(nums,domain))
			{
				cout << "Reflexive "; 
			}
			if(Symmetric(nums))
			{
				cout << "Symmetric "; 
			}
			
		}
		cout << endl;
		i++;
	}

	





	return 0; 
}

void putinArray(vector <int> &orderedpairs, int arr[MAX][MAX], int dom, int rang)
{
	const int MAX = 100; 
	
	
	for(int i = 0; i < orderedpairs.size(); i = i + 2)
	{
		arr[orderedpairs[i] - 1][orderedpairs[i+1] - 1] = 1; 
	}
}

bool RelationOrFunction(int arr[MAX][MAX], int dom, int rang)
{
	int total = 0;

	for(int i = 0; i < dom; i++)
	{
		for(int j = 0; j < rang; j++)
		{
			total = arr[i][j] + total; 
		}
		
		if(total == 1)
		{
			total = 0;
			continue; 
		}
		else
		{
				return false; 
		}
	}
	return true; 
}

int SurOrInj(int arr[MAX][MAX], int dom, int rang)
{
	int total = 0;
	
	for(int i = 0; i < dom; i++)
		{
			for(int j = 0; j < rang; j++)
			{
				total = arr[j][i] + total;
			}
			if(total >= 1)
			{
				total = 0;
				continue; 
			}
		}
		if(dom < rang)
		{
			return 1; //injective
		}
	
	for(int i = 0; i < dom; i++)
	{
		for(int j = 0; j < rang; j++)
		{
			total = arr[j][i] + total;
		}
		if(total <= 1)
		{
			total = 0;
			continue; 
		}
	}
	if(dom > rang)
	{
		return 2; //surjective
	}

	for(int i = 0; i < dom; i++)
	{
		for(int j = 0; j < rang; j++)
		{
			total = arr[j][i] + total;
		}
		if(total == 1)
		{
			total = 0;
			continue; 
		}
	}
	if(dom == rang)
	{
		return 3; //bijective
	}

	for(int i = 0; i < dom; i++)
	{
		for(int j = 0; j < rang; j++)
		{
			total = arr[j][i] + total;
		}
		if(total >= dom)
		{
			return 4; //none
		}
	}

	

}

bool Reflexive(vector <int> pairs, int dom)
{
	int j = 1;
	
	while(j <= dom)
	{
		for(int i = 0; i < pairs.size(); i = i+2)
		{
			if(pairs[i] == j && pairs[i+1] == j)
			{
				j++;
				
			}
		}
	}
	return true;
}

bool Symmetric(vector <int> pairs)
{
	int a, b;

	for(int i = 0; i < pairs.size(); i=i+2)
	{
		if(pairs[i] != pairs[i+1])
		{
			a = pairs[i]; 
			b = pairs[i+1];
			for(int j = 0; j < pairs.size(); j = j+2)
			{
				if(pairs[j] = b && pairs[j+1] == a)
				{
					return true; 
				}
			}
		}
	}
	return false; 
}



void printArray(int arr[MAX][MAX], int dom, int rang)
{
	for(int i = 0; i < dom; i++)
		{
			for(int j = 0; j < rang; j++)
			{
				cout << arr[i][j]; 
			}
			cout << endl; 
		}
}

[MiiNiPaa]

I have two questions:
1) What the problem is?
2) Why not store actual pairs in vector instead of making surrogate pairs on fly?

[hunterx893]

1) The main problem is that it does not cout "Symmetric" in the int main when running it.
2) I actually store the pairs in the vector by inputting it from the keyboard.

[MiiNiPaa]

2) I actually store the pairs in the vector by inputting it from the keyboard.

I mean to have either a vector of struct or std::pair<int, int>

Looka at the line 233: if(pairs[j] = b && pairs[j+1] == a) You are doing assigment instead of comparsion here. And compiler should issue a warning here.

GCC wrote:

main.cpp|233|warning: suggest parentheses around assignment used as truth value [-Wparentheses]|

[dhayden]

Why not use arr for the Symmetry test? Something like:

bool Symmetric(int arr[MAX][MAX])
{
    for (int i=0; i<MAX; ++i) {
        for (int j=0; j<MAX; ++j) {
            if (arr[i][j] != arr[j][i]) return false;
        }
    }
    return true;
}