Question

I’m trying to make a simple substring search using the brute force technique but I’m getting an error which I can’t see. I’m quite new to programming so please keep that in mind. The problem might be very simple.

using System;
using System.Collections;
using System.Collections.Generic;

namespace SubstringSearch
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Please enter some letters: ");
            string sequence = Console.ReadLine();
            Console.Write("Enter the sequence you want to search for: ");
            string pattern = Console.ReadLine();

            Console.WriteLine(Search(pattern, pattern.Length, sequence, sequence.Length));

            Console.ReadLine();
        }

        public static int Search(string pattern, int patternLength, string sequence, int stringLength)
        {
            int i;
            int j;

            if (stringLength >= patternLength)
            {
                for (j = 0; j <= (stringLength - patternLength); j++)
                {
                    for (i = 0; i < patternLength && pattern[i] == sequence[i + j]; i++);

                    if (i >= patternLength)
                        return j;
                    else
                        return -1;
                }
            }
            else
                return -1;
        }
    }
}

So I’m getting one error and one warning. First it tells me that not all code paths return a value ( in Search() ). I can’t see why. Second I get a warning that my integer ‘j’ is unreachable in the first for-loop (at ‘j++’).

Please help! I’m sure the answer is quite simple, but I just can’t see it.

Answer 1

The issue seems to lie in your second for loop. Try this:

 if (stringLength >= patternLength)
        {
            for (j = 0; j <= (stringLength - patternLength); j++)
            {
                for (i = 0; i < patternLength && pattern[i] == sequence[i + j]; i++)
                {
                    if (i >= patternLength)
                        return j;                       
                }
            }
        }
 return -1;

That should remove all warnings and errors and compile. Why are you not using the .Contains() method?

Contains

True if the value parameter occurs within this string, or if
value is the empty string (""); otherwise, false.