Breadth-first search (BFS) is an algorithm for traversing or searching tree or graph data structures. It starts at the tree root (or some arbitrary node of a graph, sometimes referred to as a ‘search key’ and explores the neighbor nodes first, before moving to the next level neighbors.
Source: Wikipedia
Program in C for Breadth First Search
#include<stdio.h>
#include<conio.h>
int a[20][20],q[20],visited[20],n,i,j,f=0,r=-1;
void bfs(int v)
{
for(i=1;i<=n;i++)
if(a[v][i] && !visited[i])
q[++r]=i;
if(f<=r)
{
visited[q[f]]=1;
bfs(q[f++]);
}
}
void main()
{
int v;
clrscr();
printf("n Enter the number of vertices:");
scanf("%d",&n);
for(i=1;i<=n;i++)
{
q[i]=0;
visited[i]=0;
}
printf("n Enter graph data in matrix form:n");
for(i=1;i<=n;i++)
for(j=1;j<=n;j++)
scanf("%d",&a[i][j]);
printf("n Enter the starting vertex:");
scanf("%d",&v);
bfs(v);
printf("n The node which are reachable are:n");
for(i=1;i<=n;i++)
if(visited[i])
printf("%dt",i);
else
printf("n Bfs is not possible");
getch();
}