error C2065: 'i' : undeclared identifier

[MAbebe]

Hello everyone,

Can anyone please help me figure out what I miss or did wrong to my code for not to compile?

below are the code I did and I just couldn't figure it out what I missed. Thanks.

#include <iostream>


typedef struct NodeType {
	char name;		// the node's name
	int weight;		// the node's current weight
	int pi;			// the node's parent
} Node;

int graph[6][6] = {
	{0,1,2,0,0,0},
	{1,0,5,9,0,10},
	{2,5,0,3,0,0},
	{0,9,3,0,3,0},
	{0,0,0,3,0,2},
	{0,10,0,0,2,0}
};

Node node[6];
bool visited[6];

int getMinNode() 
{
	int index = -1;
	for (int i=0; i<6; i++) 
	{
		if (!visited[i]) 
		{
			index = i;
			break;
		}
	}
	for (int j=i+1; j<6; j++) 
	{
		if (node[j].weight < node[index].weight) index = j;
	}
	return index;
}

void printResult(char *message) {
	printf("%s\n", message);
	for (int i=0; i<6; i++) {
		if (node[i].pi >= 0) {
			int parent = node[i].pi;
			printf("%c -- %c \n", node[i].name, node[parent].name);
		}
	}
}

void main() {	// Prim's algorithm
	
	// Initialize the 6 nodes
	for (int i=0; i<6; i++) {
		node[i].name = 'A'+i;
		node[i].pi = -1;		// no parent
		node[i].weight = 10000;	// 10000 as infinity
		visited[i] = false;
	}
	// Start from node 'A'
	node[0].weight = 0;
	int index = getMinNode();

	// Prim's algorithm
	while (index >= 0) {
		visited[index] = true;
		for (int j=0; j<6; j++) {
			if (j==index) continue;
			if (graph[j][index] == 0) continue;
			int weight = node[index].weight + graph[j][index];
			if (weight < node[j].weight) {
				node[j].weight = weight;
				node[j].pi = index;
			}
		}
		index = getMinNode();
	}
	
	// Print out the result
	printResult("Final Minimum Spanning Tree:");
}

[ixmike88]

hi, use code tags

for (int j=i+1; j<6; j++)

i is undefined in this line

[MAbebe]

So how can I define it?? Thanks. Please give me examples

[thelamb]

Think about what you're doing.

You want to start j at i + 1, is there any orther variable that you could use for this, that IS defined at for( int j=... ) ?

If you declare a variable inside the for statement like this, it is ONLY visible inside the for block, after that you can not use it any more (unless you re-define it).

[MasterGberry]

for (int i=0; i<6; i++) // i is defined for this block
	{
		if (!visited[i]) 
		{
			index = i;
			break;
		}
	} // i definition ends here
	for (int j=i+1; j<6; j++) // i is not defined
	{
		if (node[j].weight < node[index].weight) index = j;
	}

If you want to use i then do the following:

int i = 0; // i is now defined for the main program
for (; i<6; i++) // i is used in this block
	{
		if (!visited[i]) 
		{
			index = i;
			break;
		}
	} 
	for (int j=i+1; j<6; j++) // i is still defined since it is still in the main block
	{
		if (node[j].weight < node[index].weight) index = j;
	}

[FutureWebDev]

To fix your problem

Just put this before line 53. (I think)

int i = 0;