This is an implementation of dijkstra's algorithm in vanilla C

dijkstra.c

/*
 * Copyright @rootavish
 * LICENSE: Do whatever the fuck you want to do license.
 */
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#define N 6

int visited_all(int visited[])
{
    int i=0;

    for(i=0; i < N ; i++) {

        if (visited[i] == 0)
            return 0;
    }
    return 1;
}

int main()
{
    int visited[N];

    FILE *fp = fopen("graph.txt","r");
    int s,graph[N][N],distance[N];
    int i,j, distanceu=0, u=0, alt=0;

    if (fp == NULL) {
        fprintf(stderr,"Could not open the input file.\n");\
        return 1;
    }
    for(i=0 ;i < N ; i++) {
        for(j=0 ; j < N ; j++) {
            fscanf(fp, "%d", &graph[i][j]);
        }
    }

    printf("Enter the source vertex: ");
    scanf("%d",&s);
    s--;

    distance[s] = 0;
    for(i=0 ; i < N ; i++) {
        visited[i] = 0;
        if (i != s)
            distance[i] = INT_MAX;
    }

    while (!visited_all(visited)) {
            distanceu = INT_MAX;
            for(i=0 ; i < N ; i++) {
                if (visited[i] == 0) {
                    if (distance[i] <= distanceu) {
                        u = i;
                        distanceu = distance[u];
                    }
                }
            }

            visited[u] = 1;

            for(j=0; j < N ; j++) {
                if (j != u && graph[u][j] != -1) {
                    alt = distance[u] + graph[u][j];

                    if (alt < distance[j]) {
                        distance[j] = alt;
                    }
                }
            }
    }

    printf("The shortest paths are:\n");

    for(i=0 ; i < N ; i++) {
        if (i != s) {
            printf("Vertex %d: %d\n",i+1, distance[i]);
        }
    }
    fclose(fp);
    return 0;
}