IT. Expert System.

C

graph


A graph is a collection of nodes and edges. These nodes are connected by links(edges). These edges may be directed or undirected.

Syntax:
Syntax doesn't exist.


Example:

/*graph.c*/
#include 
#include 
#include "graph.h"
 
/* Function to create an adjacency list node*/
adjlist_node_p createNode(int v)
{
    adjlist_node_p newNode = (adjlist_node_p)malloc(sizeof(adjlist_node_t));
    if(!newNode)
        err_exit("Unable to allocate memory for new node");
 
    newNode->vertex = v;
    newNode->next = NULL;
 
    return newNode;
}
 
/* Function to create a graph with n vertices; Creates both directed and undirected graphs*/
graph_p createGraph(int n, graph_type_e type)
{
    int i;
    graph_p graph = (graph_p)malloc(sizeof(graph_t));
    if(!graph)
        err_exit("Unable to allocate memory for graph");
    graph->num_vertices = n;
    graph->type = type;
 
    /* Create an array of adjacency lists*/
    graph->adjListArr = (adjlist_p)malloc(n * sizeof(adjlist_t));
    if(!graph->adjListArr)
        err_exit("Unable to allocate memory for adjacency list array");
 
    for(i = 0; i < n; i++)
    {
        graph->adjListArr[i].head = NULL;
        graph->adjListArr[i].num_members = 0;
    }
 
    return graph;
}
 
/*Destroys the graph*/
void destroyGraph(graph_p graph)
{
    if(graph)
    {
        if(graph->adjListArr)
        {
            int v;
            /*Free up the nodes*/
            for (v = 0; v < graph->num_vertices; v++)
            {
                adjlist_node_p adjListPtr = graph->adjListArr[v].head;
                while (adjListPtr)
                {
                    adjlist_node_p tmp = adjListPtr;
                    adjListPtr = adjListPtr->next;
                    free(tmp);
                }
            }
            /*Free the adjacency list array*/
            free(graph->adjListArr);
        }
        /*Free the graph*/
        free(graph);
    }
}
 
/* Adds an edge to a graph*/
void addEdge(graph_t *graph, int src, int dest)
{
    /* Add an edge from src to dst in the adjacency list*/
    adjlist_node_p newNode = createNode(dest);
    newNode->next = graph->adjListArr[src].head;
    graph->adjListArr[src].head = newNode;
    graph->adjListArr[src].num_members++;
 
    if(graph->type == UNDIRECTED)
    {
        /* Add an edge from dest to src also*/
        newNode = createNode(src);
        newNode->next = graph->adjListArr[dest].head;
        graph->adjListArr[dest].head = newNode;
        graph->adjListArr[dest].num_members++;
    }
}
 
/* Function to print the adjacency list of graph*/
void displayGraph(graph_p graph)
{
    int i;
    for (i = 0; i < graph->num_vertices; i++)
    {
        adjlist_node_p adjListPtr = graph->adjListArr[i].head;
        printf("\n%d: ", i);
        while (adjListPtr)
        {
            printf("%d->", adjListPtr->vertex);
            adjListPtr = adjListPtr->next;
        }
        printf("NULL\n");
    }
}
 
int main()
{
    graph_p undir_graph = createGraph(5, UNDIRECTED);
    graph_p dir_graph = createGraph(5, DIRECTED);
    addEdge(undir_graph, 0, 1);
    addEdge(undir_graph, 0, 4);
    addEdge(undir_graph, 1, 2);
    addEdge(undir_graph, 1, 3);
    addEdge(undir_graph, 1, 4);
    addEdge(undir_graph, 2, 3);
    addEdge(undir_graph, 3, 4);
 
    addEdge(dir_graph, 0, 1);
    addEdge(dir_graph, 0, 4);
    addEdge(dir_graph, 1, 2);
    addEdge(dir_graph, 1, 3);
    addEdge(dir_graph, 1, 4);
    addEdge(dir_graph, 2, 3);
    addEdge(dir_graph, 3, 4);
 
    printf("\nUNDIRECTED GRAPH");
    displayGraph(undir_graph);
    destroyGraph(undir_graph);
 
    printf("\nDIRECTED GRAPH");
    displayGraph(dir_graph);
    destroyGraph(dir_graph);
 
    return 0;
}


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