# Create the Shortest Path Finder with Dijkstra's Algorithm in C

In this guide, we will guide you through the process of finding the shortest path on a graph using Dijkstra's algorithm in the C programming language. This is a fundamental concept in graph theory and is often used to solve real-world problems, such as finding the shortest route between locations on a map or optimizing network routing. Understanding how Dijkstra's algorithm works and implementing it in C will equip you with a powerful tool for tackling complex optimization challenges, making it a valuable skill for students, programmers, and anyone interested in algorithmic problem-solving.

## Exploring Dijkstra's Algorithm for Shortest Path in C

Explore Dijkstra's Algorithm for Shortest Path in C on our website, where we provide comprehensive guidance and practical examples. If you need help with your C assignment, this resource will equip you with valuable insights to tackle complex optimization challenges. Whether you're a student aiming to enhance your programming skills or a professional seeking solutions for real-world graph problems, our content offers the knowledge and support you need to succeed. Discover the power of Dijkstra's Algorithm and its applications in C programming.

## Block 1: Main Function

``````c #include #include #include "structname.h" int main() { // Prompt for the file to be processed and load it as a graph object printf("Enter File Name:\n"); char filename[MAX_STR_LEN]; fgets(filename, MAX_STR_LEN, stdin); filename[strlen(filename) - 1] = '\0'; Graph* graph = loadGraph(filename); // Prompt for the starting node and calculate shortest paths printf("Start Node:\n"); char line[MAX_STR_LEN]; int startingNode; fgets(line, MAX_STR_LEN, stdin); sscanf(line, "%d", &startingNode); printf("Running Dijkstra on graph.\n"); printf("Input File: %s\n", filename); printf("Start Node: %d\n", startingNode); findShortestPath(graph, startingNode); // Clean up and exit freeGraph(graph); return 0; } ``````
• This block is the main function that orchestrates the program.
• It first asks for the filename containing graph data and the starting node.
• Then, it calls the `loadGraph` function to load the graph data.
• After loading the graph, it calls the `findShortestPath` function to calculate the shortest paths.
• Finally, it releases memory and exits.

``````c Graph* loadGraph(const char* filename) { // Attempt to open the file, terminate the program if the file does not exist or cannot be read. FILE* file = fopen(filename, "r"); if (!file) { printf("Error: Failed to open the file.\n"); exit(1); } // Load the number of vertices and the connections between them Graph* graph = (Graph*)malloc(sizeof(Graph)); fscanf(file, "%d", &graph->size); graph->distances = (int**)malloc(sizeof(int*) * graph->size); for (int i = 0; i < graph->size; i++) graph->distances[i] = (int*)malloc(sizeof(int) * graph->size); // Vertices have no connection to each other by default, hence the distance is set to 0. int fromVertex, toVertex; for (fromVertex = 0; fromVertex < graph->size; fromVertex++) for (toVertex = 0; toVertex < graph->size; toVertex++) graph->distances[fromVertex][toVertex] = 0; // Now connect the vertices int distance; while (fscanf(file, "%d %d %d", &fromVertex, &toVertex, &distance) == 3) graph->distances[fromVertex][toVertex] = distance; return graph; } ``````
• This block defines the `loadGraph` function that reads the graph data from a file.
• It opens the file, reads the number of vertices, and creates a graph structure.
• It then connects vertices based on the input file and returns the graph.

## Block 3: Freeing the Graph

``````c void freeGraph(Graph* graph) { for (int i = 0; i < graph->size; i++) free(graph->distances[i]); free(graph->distances); free(graph); } ``````
• This block defines the `freeGraph` function, which frees memory allocated for the graph structure.

## Block 4: Dijkstra's Algorithm

``````c void findShortestPath(Graph* graph, int startingNode) { // Make sure that the starting node exists in the graph if (startingNode < 0 || startingNode >= graph->size) { printf("Error: Invalid starting node.\n"); return; } // Make a node object for each node to encapsulate information Node* nodes = (Node*)malloc(sizeof(Node) * graph->size); for (int i = 0; i < graph->size; i++) { nodes[i].distance = INT_MAX; nodes[i].isVisited = FALSE; } // The starting node will start at distance 0 nodes[startingNode].distance = 0; // Now we do the shortest path algorithm while (TRUE) { // Find the next node to be processed, the one with the shortest distance int nextNode = -1; for (int node = 0; node < graph->size; node++) { if (!nodes[node].isVisited) { // Smaller distance wins; if distances are equal, the smaller node index wins if (nextNode == -1 || nodes[node].distance < nodes[nextNode].distance) nextNode = node; } } if (nextNode == -1 || nodes[nextNode].distance == INT_MAX) break; nodes[nextNode].isVisited = TRUE; // Calculate the distance from the chosen next node to adjacent ones that haven't been visited for (int adjacentNode = 0; adjacentNode < graph->size; adjacentNode++) { if (!nodes[adjacentNode].isVisited && graph->distances[nextNode][adjacentNode] > 0) { int adjacentDistance = nodes[nextNode].distance + graph->distances[nextNode][adjacentNode]; // Always prefer to choose the shorter distance if (adjacentDistance < nodes[adjacentNode].distance) nodes[adjacentNode].distance = adjacentDistance; } } } // When the code reaches here, we have calculated the shortest distance from the starting node to all other nodes printf("Shortest Distances\n"); for (int node = 0; node < graph->size; node++) { printf("Shortest Path From %d to %d is ", startingNode, node); if (nodes[node].distance == INT_MAX) printf("Infinity"); else printf("%d", nodes[node].distance); printf("\n"); } free(nodes); } ``````
• This block defines the `findShortestPath` function, which implements Dijkstra's algorithm.
• It initializes data structures, such as an array of nodes, for the algorithm.
• It then performs Dijkstra's algorithm to find the shortest paths from the starting node to all other nodes.
• Finally, it prints the results, showing the shortest distances from the starting node to each node.

## Block 5: Constants and Structures

``````c #define MAX_STR_LEN 100 #define TRUE 1 #define FALSE 0 typedef struct Graph Graph; struct Graph { int** distances; /**< A 2 dimensional array that keeps track the connection of vertices. The indices of the array are the vertices, the content are the distances. */ int size; /**< The number of vertices in the graph */ }; typedef struct Node Node; struct Node { int distance; /**< Estimated sorted distance from this node to a chosen shortest path to another node */ int isVisited; /**< Indicates if the node has been processed or not when doing Dijkstra's algorithm */ }; ``````
• This block defines constants and structures used in the program.
• It includes the definition of the `Graph` structure, which holds the graph data.
• It defines the `Node` structure, which is used in Dijkstra's algorithm.
• It also sets some constants for readability.

## Conclusion

By following this guide, you'll gain a strong foundation in implementing Dijkstra's algorithm in C, which can be applied to various graph-related problems. Whether you're a student looking for programming homework help or a programmer seeking to enhance your knowledge, this guide will provide valuable insights and practical examples. With this newfound knowledge, you'll be better equipped to tackle real-world challenges, from optimizing transportation routes to network pathfinding. The ability to find the shortest path efficiently is a highly sought-after skill in the fields of computer science, data analysis, and beyond, making this guides a valuable resource for your journey into the world of algorithms and problem-solving.