c语言建立无向图

要建立一个无向图，可以使用邻接表来进行表示。邻接表是一种数据结构，用于表示图中每个节点所有相邻节点的集合。

下面是一个示例代码，可以创建一个无向图：

#include <stdio.h>
#include <stdlib.h>

typedef struct Node {
    int vertex;
    struct Node* next;
} Node;

typedef struct Graph {
    int num_vertices;
    Node** adj_list;
} Graph;

Node* create_node(int v) {
    Node* node = (Node*)malloc(sizeof(Node));
    node->vertex = v;
    node->next = NULL;
    return node;
}

Graph* create_graph(int num_vertices) {
    Graph* graph = (Graph*)malloc(sizeof(Graph));
    graph->num_vertices = num_vertices;

    graph->adj_list = (Node**)malloc(num_vertices * sizeof(Node*));

    for (int i = 0; i < num_vertices; ++i) {
        graph->adj_list[i] = NULL;
    }

    return graph;
}

void add_edge(Graph* graph, int src, int dest) {
    Node* node = create_node(dest);
    node->next = graph->adj_list[src];
    graph->adj_list[src] = node;

    node = create_node(src);
    node->next = graph->adj_list[dest];
    graph->adj_list[dest] = node;
}

void print_graph(Graph* graph) {
    for (int i = 0; i < graph->num_vertices; ++i) {
        Node* tmp = graph->adj_list[i];
        printf("\nAdjacency list of vertex %d\n head ", i);
        while (tmp) {
            printf("-> %d", tmp->vertex);
            tmp = tmp->next;
        }
        printf("\n");
    }
}

int main() {
    Graph* graph = create_graph(4);
    add_edge(graph, 0, 1);
    add_edge(graph, 0, 2);
    add_edge(graph, 1, 2);
    add_edge(graph, 2, 3);

    print_graph(graph);

    return 0;
}

上面的代码创建了一个有四个节点的无向图，并在它们之间添加了几条边。您可以根据需要修改该代码以创建更大或更小的无向图。