Converting an Adjacency Matrix to an Adjacency List in C - c

Question

I am supposed to convert a given adjacency matrix to an adjacency list in C. I need this adjacency list because this is where I will implement my algorithm for Depth First Search (DFS). Before I write my code for DFS, I wanna make sure that I made the right adjacency list. However, my problem is that when I try to run my code, the program does not proceed in printing the graph. I believe it's because of how I read user inputs because that is exactly where the program stops. Now my question is, how do I read multiple inputs in one line? I tried using fgets() but my program does not proceed in printing the graph/adjacency list. Provided below is the code that I wrote.
Here are the struct nodes:
typedef struct vertexnode VertexNode;
struct vertexnode
{
int vertex;
VertexNode *Next;
};
typedef struct graph
{
int numVertices;
VertexNode **adjLists;
} Graph;
Below is the main function:
int main()
{
int size, i, temp;
//char input1[100000];
scanf("%d\n", &size); // scan number of vertices
Graph *graph = createAGraph(size);
for(i = 0; i < size; i++) // scan the adjacency MATRIX
{
char input1[100000];
int j = 0;
fgets(input1, sizeof(input1), stdin);
char *piece = strtok(input1, " "); // extract first number
while(piece != NULL)
{
temp = atoi(piece); // convert from char to int
if(temp == 1) // create new node
{
addEdge(graph, i, j); //add edge from vertex i to j
}
j++;
piece = strtok(NULL, " ");
}
}
printGraph(graph);
return 0;
}
Function for creating a vertex:
VertexNode *createVertex(int vertexNum)
{
VertexNode *new_vertex = (VertexNode *) malloc(sizeof(VertexNode));
new_vertex->vertex = vertexNum + 1;
new_vertex->Next = NULL;
return new_vertex;
}
Function for creating the graph:
Graph *createAGraph(int size)
{
Graph *graph = (Graph *)malloc(sizeof(Graph));
graph->numVertices = size;
graph->adjLists = (VertexNode **)malloc(sizeof(VertexNode *));
for(int i = 0; i < size; i++)
graph->adjLists[i] = NULL;
return graph;
}
Function for addEdge:
void addEdge(Graph *graph, int s, int d)
{
VertexNode *newNode = createVertex(d);
newNode->Next = graph->adjLists[s];
graph->adjLists[s] = newNode;
}
Function for printing the adjacency list:
void printGraph(Graph *graph)
{
for(int i = 0; i < graph->numVertices; i++)
{
VertexNode *temp = graph->adjLists[i];
printf("\n Vertex %d\n: ", i+1);
while(temp)
{
printf("%d -> ", temp->vertex);
temp = temp->Next;
}
newline;
}
}
Is there a better way of taking a user input given the context that we have to read multiple inputs in a line and there's an arbitrary number of lines?
Example Input:
4
0 0 1 0
1 0 0 1
1 1 0 1
0 1 0 0
First input is the number of vertices in the list
The succeeding lines represent the adjacency matrix
The adjacency list should be like this:
1 -> 3
2 -> 1 -> 4
3 -> 1 -> 2 -> 4
4 -> 2

Answer 1

Would you please try the following:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int
main()
{
int i, j, size;
char *tk; // pointer to a token
char delim[] = " "; // delimiter of tokens
char line[BUFSIZ];
int *m; // matrix
fgets(line, BUFSIZ, stdin); // read stdin and assign line
size = atoi(line); // size of matrix
if (NULL == (m = malloc(sizeof(int) * size * size))) {
// allocate a matrix
fprintf(stderr, "malloc failed\n");
exit(1);
}
for (i = 0; i < size; i++) {
if (NULL == fgets(line, BUFSIZ, stdin)) {
fprintf(stderr, "insufficient lines\n");
exit(1);
}
j = 0;
tk = strtok(line, delim);
while (tk != NULL) {
m[i * size + j] = atoi(tk); // assign element of matrix
j++;
if (j > size) {
fprintf(stderr, "too many columns\n");
exit(1);
}
tk = strtok(NULL, delim);
}
if (j < size) {
fprintf(stderr, "insufficient columns\n");
exit(1);
}
}
// print the adjacency list
for (i = 0; i < size; i++) {
printf("%d", i + 1);
for (j = 0; j < size; j++) {
if (m[i * size + j]) {
printf(" -> %d", j + 1);
}
}
printf("\n");
}
return 0;
}
As I'm not aware of your special functions such as createAGraph() or
addEdge(), I've used my own definition of matrix. Please modify
my code to meet your interfaces.