Question

这是我的代码。这将使用户的信息很好，但它不会调用prims！（它甚至不会在通话前打印语句..）。问题是，这个main（）只是使用kruskals而不是prims从这个问题的尝试中复制和粘贴..主要没有改变，它曾经工作正常，唯一的区别是prims（）现在有。我看不出任何理由为什么程序会停止（然后什么也不做。闪烁光标没什么）。发生了什么事？

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define MAX 50

typedef struct graph{
    int vertices;
    int edges;
    int vertex[MAX];
    int edge[MAX][4]; /*[i][0]=i (edge ref) [i][1]=vertex1 [i][2]=vertex2 [i][3]=weight*/
} Graph;

void prims(Graph graph);

int main () {

    Graph* graph=malloc(sizeof *graph);
    printf("Please enter the number of vertices in your graph: ");
    scanf("%i", &graph->vertices);
    printf("\nPlease enter the number of edges in your graph: ");
    scanf("%i", &graph->edges);

    for (int i=0; i<graph->edges; ++i) {
        graph->edge[i][0]=i;
    ensure_valid_input:
        printf("\nPlease enter the vertices connected by edge %i, and its weight: ",i+1);
        scanf("%i %i %i", &graph->edge[i][1], &graph->edge[i][2], &graph->edge[i][3]);
        if (graph->edge[i][1]>graph->vertices || graph->edge[i][2]>graph->vertices || graph->edge[i][1] <= 0 || graph->edge[i][2] <= 0) {
            printf("\nERROR: One of these vertices is invalid; ensure they are both in range 1 - %d\n", graph->vertices);
            goto ensure_valid_input;
        }
    }

    printf("Try to call the function?");

    prims(*graph);

    /*Print result to screen*/

    /*Print result to file*/

    return 0;
}


void prims(Graph graph){

    printf("Function called...");

    /*Initialise sets and test-values*/

    int edges_ordered[graph.edges];
    int used_vertices[graph.vertices];
    int used_edges[graph.vertices-1];
    int least_avail_edge;
    int least_edge_reset;
    int existing_entry;
    int done=1;
    int vertex_present;

    for (int i=0; i<graph.vertices; ++i) {
        if (i=0) {
            used_vertices[i]=0;
        }
        else {
            used_vertices[i]=-1;
        }

    }

    /*Order the edges*/

    for (int i=0; i<graph.edges; ++i) {
        least_avail_edge = least_edge_reset;
        existing_entry = 1;
        for (int j=0; j<graph.edges; ++j) {
            if (graph.edge[j][3]<=graph.edge[least_avail_edge][3]) {
                for (int k=0; k<graph.edges; ++k) {
                    if (edges_ordered[k]==graph.edge[j][0]) {
                        existing_entry=0;
                    }
                }
                if (existing_entry==1) {
                    least_avail_edge=j;
                }
            }
        }
        edges_ordered[i]=least_avail_edge;
    }

    //Diagnotstic Print

    for (int i=0; i<graph.edges; ++i) {
        printf("\n%d) Edge %d, Weight %d\n)", i+1, edges_ordered[i]+1, graph.edge[i][3]);
    }



    /*Continually add next appropriate edge to tree until spanning*/

    while (done!=0) {



        /*Test to see if all vertices are in the tree yet*/
        done=0;
        for (int i=0; i<graph.vertices; ++i) {
            vertex_present=1;
            for (int j=0; j<graph.vertices; ++j) {
                if (graph.vertex[i]==used_vertices[j]) {
                    vertex_present=0;
                }
            }
            if (vertex_present==1) {
                /*Vertex is missing from tree -- not done!*/
                done=1;
                break;
            }
        }
    }
}

Answer 1

此代码存在很多问题，但我怀疑罪魁祸首在prims()函数中：

if (i=0) {

我认为你的意思是==。您每次循环都将i设置为零，这会导致循环永不终止，冻结您的程序。

其他问题是least_edge_reset未初始化，malloc的返回值未被强制转换（取决于C / C ++版本和编译器设置，您是否会收到错误或警告），sizeof *graph很尴尬。此外，没有防止超过最大边数等的保护，但我会停在那里，因为它不是你所问的。

我怀疑你的print语句正在运行，但由于没有\n，它正在被缓冲而不会立即显示在屏幕上，因为prims()被卡住而永远不会显示在无限循环中。

程序停止并无缘无故地执行任何操作

1 个答案: