Question

I’m attempting to code Prim’s algorithm. However when I compile I get errors on lines: 57,59,60,62,63,65

Obviously it was something to do with my arrays… I just don’t know what exactly. I get the feeling it has to do with pointers which I have tried to figure out and have failed.

int map[][7] is a global array I am using to keep track of my initial graph.

edit – as requested here is all of the code

#include <iostream>

using namespace std;

void performPrims(int);
void print(int *);

// Global Variables
int nodes = 7;
int cur   = 0;
int cost  = 0;

int map[][7] =  
   {{0,3,6,0,0,0,0},
    {3,0,7,0,0,12,0},
    {6,7,0,10,13,8,0},
    {0,0,10,0,0,0,5},
    {0,0,13,0,0,9,4},
    {0,12,8,0,9,0,11},
    {0,0,0,5,4,11,0}};

int main()
{
// Initializations

srand(time(NULL)); 
int S = rand() % 7; // Create an arbitrary starting point

// Perform Prim's Algorithm starting with S

performPrims(S);

return 0;
}

void performPrims(int S)
{
int low = 100;

// open[] is used to keep track of what vertices are available
int open [] = {1,2,3,4,5,6,7};

// closed [] is used to keep track of what vertices have been reached and in what order
int closed [] = {0,0,0,0,0,0,0};

open [S] = 0;       // Make our starting node unavailable
closed [cur] = S+1; // Record our starting node in the path
cur++;

while (cur < 7)
{
    int i=0;
    while (i<nodes)
    {
        int k=0;
        while (k<nodes)
        {
            if (*map[*close[i]-1][k] > 0 && *map[*close[i]-1][k] < low)
            {
                low = map[close[i]-1][k];
                close [cur] = k+1;
            }
            map[close[cur-1]-1][close[cur]-1] = 0;
            map[close[cur]-1][close[cur-1]-1] = 0;
            cost += low; low = 100;
            open[close[cur]-1] = 0;
            k++;
        }
        i++;
    }
    cur++;
}
print(closed);
}

void print(int *closed)
{
cout<<"The path taken was ";
for (int i=0; i<nodes; i++)
    cout<<closed[i]<<" "<<endl;
cout<<"\nThe cost is "<<cost<<endl;
}

Errors

There are a few different ones:

error: pointer to a function used in arithmetic (Many Lines)
error: invalid types ‘int[7][7][int (*)(int)]’ for array subscript (Many Lines)
error: assignment of read-only location (LINE 60)
error: cannot convert ‘int’ to ‘int ()(int)’ in assignment (LINE 60)

Answer 1

You misspelled closed. You typed close instead.

Replace all instances of close with closed.

Also, add #include <cstdlib> to the top of the file.