Depth First Traversal in C
We shall not see the implementation of Depth First Traversal (or Depth First Search) in C programming language. For our reference purpose, we shall follow our example and take this as our graph model −

Implementation in C
#include <stdio.h> #include <stdlib.h> #include <stdbool.h> #define MAX 5 struct Vertex { char label; bool visited; }; //stack variables int stack[MAX]; int top = -1; //graph variables //array of vertices struct Vertex* lstVertices[MAX]; //adjacency matrix int adjMatrix[MAX][MAX]; //vertex count int vertexCount = 0; //stack functions void push(int item) { stack[++top] = item; } int pop() { return stack[top--]; } int peek() { return stack[top]; } bool isStackEmpty() { return top == -1; } //graph functions //add vertex to the vertex list void addVertex(char label) { struct Vertex* vertex = (struct Vertex*) malloc(sizeof(struct Vertex)); vertex->label = label; vertex->visited = false; lstVertices[vertexCount++] = vertex; } //add edge to edge array void addEdge(int start,int end) { adjMatrix[start][end] = 1; adjMatrix[end][start] = 1; } //display the vertex void displayVertex(int vertexIndex) { printf("%c ",lstVertices[vertexIndex]->label); } //get the adjacent unvisited vertex int getAdjUnvisitedVertex(int vertexIndex) { int i; for(i = 0; i < vertexCount; i++) { if(adjMatrix[vertexIndex][i] == 1 && lstVertices[i]->visited == false) { return i; } } return -1; } void depthFirstSearch() { int i; //mark first node as visited lstVertices[0]->visited = true; //display the vertex displayVertex(0); //push vertex index in stack push(0); while(!isStackEmpty()) { //get the unvisited vertex of vertex which is at top of the stack int unvisitedVertex = getAdjUnvisitedVertex(peek()); //no adjacent vertex found if(unvisitedVertex == -1) { pop(); } else { lstVertices[unvisitedVertex]->visited = true; displayVertex(unvisitedVertex); push(unvisitedVertex); } } //stack is empty, search is complete, reset the visited flag for(i = 0;i < vertexCount;i++) { lstVertices[i]->visited = false; } } int main() { int i, j; for(i = 0; i < MAX; i++) { // set adjacency for(j = 0; j < MAX; j++) // matrix to 0 adjMatrix[i][j] = 0; } addVertex('S'); // 0 addVertex('A'); // 1 addVertex('B'); // 2 addVertex('C'); // 3 addVertex('D'); // 4 addEdge(0, 1); // S - A addEdge(0, 2); // S - B addEdge(0, 3); // S - C addEdge(1, 4); // A - D addEdge(2, 4); // B - D addEdge(3, 4); // C - D printf("Depth First Search: "); depthFirstSearch(); return 0; }
If we compile and run the above program, it will produce the following result −
Output
Depth First Search: S A D B C
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