﻿ C Program to add Vertex to an existing Graph

Add Vertex to existing Graph: C Program Example

C Program to implement Graph Structure: Exercise-2 with Solution

Write a C program that implements a function to add a new vertex to an existing graph.

Vertices are represented by numbers 1, 2, 3, and 4.

Edges are represented by lines connecting the vertices.

Sample Solution:

C Code:

``````#include <stdio.h>

#define MAX_VERTICES 100

// Function to display the adjacency matrix
void displayGraph(int graph[MAX_VERTICES][MAX_VERTICES], int vertices) {
for (int i = 0; i < vertices; i++) {
for (int j = 0; j < vertices; j++) {
printf("%d ", graph[i][j]);
}
printf("\n");
}
}

// Function to add a new vertex to the graph
void addVertex(int graph[MAX_VERTICES][MAX_VERTICES], int* vertices) {
if (*vertices >= MAX_VERTICES) {
printf("Cannot add more vertices. Maximum limit reached.\n");
return;
}

// Increment the number of vertices
(*vertices)++;

for (int i = 0; i < *vertices; i++) {
graph[i][*vertices - 1] = 0;
graph[*vertices - 1][i] = 0;
}

}

int main() {
int vertices, edges;

// Input the number of vertices
printf("Enter the number of vertices: ");
scanf("%d", &vertices);

if (vertices <= 0 || vertices > MAX_VERTICES) {
printf("Invalid number of vertices. Exiting...\n");
return 1;
}

int graph[MAX_VERTICES][MAX_VERTICES] = {0}; // Initialize the adjacency matrix with zeros

// Input the number of edges
printf("Enter the number of edges: ");
scanf("%d", &edges);

if (edges < 0 || edges > vertices * (vertices - 1) / 2) {
printf("Invalid number of edges. Exiting...\n");
return 1;
}

// Input edges and construct the adjacency matrix
for (int i = 0; i < edges; i++) {
int start, end;
printf("Enter edge %d (start end): ", i + 1);
scanf("%d %d", &start, &end);

// Validate input vertices
if (start < 0 || start >= vertices || end < 0 || end >= vertices) {
printf("Invalid vertices. Try again.\n");
i--;
continue;
}

graph[start][end] = 1;
graph[end][start] = 1; // For undirected graph
}

// Display the original adjacency matrix
printf("Original Graph:\n");
displayGraph(graph, vertices);

// Display the modified adjacency matrix
printf("Graph after adding a new vertex:\n");
displayGraph(graph, vertices);

return 0;
}
```
```

Output:

```Enter the number of vertices: 4
Enter the number of edges: 3
Enter edge 1 (start end): 0 1
Enter edge 2 (start end): 1 2
Enter edge 3 (start end): 2 3
Original Graph:
0 1 0 0
1 0 1 0
0 1 0 1
0 0 1 0
Graph after adding a new vertex:
0 1 0 0 0
1 0 1 0 0
0 1 0 1 0
0 0 1 0 0
0 0 0 0 0
```

Explanation:

In the exercise above,

• Display Function (displayGraph):
• Prints the adjacency matrix of the graph.
• Checks if the maximum limit of vertices (MAX_VERTICES) has been reached.
• Increments the number of vertices (vertices) and adds the new vertex connections to the existing graph.
• Main Function (main):
• Inputs the number of vertices and edges from the user.
• Constructs the initial graph based on user input.
• Displays the original adjacency matrix.

Flowchart:

C Programming Code Editor:

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