Pattern matching

[VanKha]

I write this program for pattern-matching,but it gives wrong result:

#include<iostream>
#include<conio.h>
#include<string.h>
using namespace std;
main()
{
    char text[100],pat[10];
    cout<<"text:";cin>>text;
    cout<<" pattern:";cin>>pat;
    int pos=0,i=0,j=0;
    while((i<=strlen(pat))&&(j<=strlen(text)))
    {
        if(pat[i]==text[j])
        {
            i++;
            j++;
        }
        else
        {
            pos++;
            j=pos;
            i=0;
        }
 
    }
    if(i>strlen(pat))
        cout<<"Matching occurs from"<<pos+1;
    else
        cout<<"No matching ";
}
 

For example,I enter
text:asm
pattern:a
result:No matching!
I think the algo is right,but why it gives such wrong result??

[JosAH]

I write this program for pattern-matching,but it gives wrong result:

#include<iostream>
#include<conio.h>
#include<string.h>
using namespace std;
main()
{
    char text[100],pat[10];
    cout<<"text:";cin>>text;
    cout<<" pattern:";cin>>pat;
    int pos=0,i=0,j=0;
    while((i<=strlen(pat))&&(j<=strlen(text)))
    {
        if(pat[i]==text[j])
        {
            i++;
            j++;
        }
        else
        {
            pos++;
            j=pos;
            i=0;
        }
 
    }
    if(i>strlen(pat))
        cout<<"Matching occurs from"<<pos+1;
    else
        cout<<"No matching ";
}
 

For example,I enter
text:asm
pattern:a
result:No matching!
I think the algo is right,but why it gives such wrong result??

Congratulations for hitting that (in)famous OBOE (Off By One Error). Check the
conditions in the while clause: change both '<=' to '<' and you're in busyness.
Also adjust the condition in that last if clause accordingly.

kind regards,

Jos (<--- been bitten by the OBOE too many times ;-)