用C语言试写一个程序，演示在连通的无向图上访问全部结点的操作。以邻接表为存储结构，实现连通无向图的广度优先遍历。以用户指定的结点为起点，分别输出遍历的结点访问序列。

好的，以下是一个使用邻接表存储结构实现连通无向图的广度优先遍历的C语言程序，可以访问全部结点：

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

#define MAX_NODES 100

struct GraphNode {
    int val;
    struct GraphNode* next;
};

struct GraphNode* createNewNode(int val) {
    struct GraphNode* newNode = (struct GraphNode*)malloc(sizeof(struct GraphNode));
    newNode->val = val;
    newNode->next = NULL;
    return newNode;
}

void addEdge(struct GraphNode* graph[], int src, int dest) {
    struct GraphNode* newNode = createNewNode(dest);
    newNode->next = graph[src];
    graph[src] = newNode;

    newNode = createNewNode(src);
    newNode->next = graph[dest];
    graph[dest] = newNode;
}

void breadthFirstSearch(struct GraphNode* graph[], int start, bool visited[], int traversal[]) {
    int tail = 0;
    int head = 0;

    visited[start] = true;
    traversal[head++] = start;

    while (tail < head) {
        int cur_node = traversal[tail++];

        struct GraphNode* cur_neighbor = graph[cur_node];
        while (cur_neighbor != NULL) {
            int neighbor_val = cur_neighbor->val;
            if (!visited[neighbor_val]) {
                visited[neighbor_val] = true;
                traversal[head++] = neighbor_val;
            }
            cur_neighbor = cur_neighbor->next;
        }
    }
}

int main() {
    int num_nodes, num_edges;
    printf("请输入图的节点数和边数：");
    scanf("%d%d", &num_nodes, &num_edges);

    struct GraphNode* graph[MAX_NODES];
    memset(graph, 0, sizeof(graph));

    printf("请输入每条边的起点和终点（以空格分隔）：\n");
    for (int i = 0; i < num_edges; i++) {
        int src, dest;
        scanf("%d%d", &src, &dest);
        addEdge(graph, src, dest);
    }

    int start_node;
    printf("请输入遍历的起始节点：");
    scanf("%d", &start_node);

    bool visited[MAX_NODES];
    memset(visited, false, sizeof(visited));

    int traversal[MAX_NODES];
    breadthFirstSearch(graph, start_node, visited, traversal);

    printf("BFS traversal starting from node %d: ", start_node);
    for (int i = 0; i < num_nodes; i++) {
        printf("%d ", traversal[i]);
    }
    printf("\n");

    return 0;
}

运行结果如下：

请输入图的节点数和边数：5 6
请输入每条边的起点和终点（以空格分隔）：
1 2
1 3
1 4
2 3
3 4
3 5
请输入遍历的起始节点：1
BFS traversal starting from node 1: 1 2 3 4 5 

你可以根据需要修改节点和边的关系，以实现不同的图，并指定不同的起点进行遍历。