Thread: Finding substrings with arrays...need help

Write a C program that allows the user to enter two strings s1 and s2 and checks if s2 is a subtring of s1. If this is the case, it reports the index of s1 at which an instance of s2 is present, otherwise it reports that the substring was not found. For example, cat and nate are two subtrings of concatenate. (The only library functions you are allowed to use are printf and fgets). Your program must print appropriate prompts and messages.

Here is my code so far:

Code:

#include <stdio.h>

int main()
{
	
	char s1[6];
	char s2[6];
	char temp[255];

	int i,j,k=1;
	

	printf("\nEnter first string1 (word 5 characters or less): ");
	fgets(s1, 6, stdin);

        gets(temp);

	printf("\nEnter substring to find in string1 (word 5 characters or less): ");
	fgets(s2, 6, stdin);

	for(i=0; i<6; i++)
	{
		for(j=0; j<6; j++)
		{
			if(s2[i]==s1[j])
			{
				//printf("&#37;c%c\n", s2[i], s1[j]);

				//break;
			}

			
		}
	}


	

return(0);
}

Right now, I have it so that the user inputs a 5 word character for s1 and s2. I have the for loop as a setup to check if s2 has the same characters as s1. The problem I am having is trying to report that the index of s1 at which an instance of s2 is present, otherwise it not being found...

I was thinking about trying to use a way to use true and false flags so that if s2 is true (meaning it is present in s1), then it would print a message. If s2 is false (meaning s2 is not present in s1), then it would say substring was not found. I don't understand how to implement it...

What would be the best way?

Can anyone help me out??

Gets is bad: http://cpwiki.sf.net/gets.
Further, fgets reads the entire line (unless they enter more than 5 chars), so gets is unnecessary.
For the loop, you should loop the actual length of the string and no more or less, because there may be junk in there (and it will of course react because both strings contains \0 at the end), so use strlen to get the length of the strings.
As for the logic, one way I see is the make an additional loop inside your if. You could use a flag there as well, that is set to true initially. The loop will check if each subsequent character matches. An example of what I mean:

If the entered string is: concatenate
And you search for nate.
If it finds the 'n', you enter another loop. This will check if the next char is equal to the second character in the string you're trying to match, in this example, 'a'. If it doesn't match, then set flag to false and break loop.
Then continue for the third character, fourth, and so on .

Good luck.

also fgets is not allowed by the assignment
and sample string concatenate will not pass into the array of 6 characters - so you definitely need larger array for the string to be searched

in your inner loop note that the searched string could be shorted than 6 characters - fro example 3 like cat - so it will not fill the whole buffer

And you should break the inner loop as soon as not matched character found - to start checking the next subsequence of characters in the original string

And if you go to the nul-character of the searched string without breaking the inner loop - you have found your matchand should report the results

and think about
concatenate and
cat
you will find your match when i == 3
but you should check in the inner loop
s1[i] == s2[0] == 'c' (j == 0)
s1[i+1] == s2[1] == 'a' (j == 1)
s1[i+2] == s2[2] == 't' (j == 2)

in your code you are comparing all the characters of the cat-string to the 'c' character of the originat string

I don't know why they would restrict the use of all library functions. Obviously, I understand why they wouldn't want you to use functions for string searching and matching, but input functions, such as fgets?

Anyway, since it says only scanf is allowed, I suggest you read this: http://cboard.cprogramming.com/showp...37&postcount=9
It touches the topic about reading strings with scanf.

Professors rarely do teach material. Outsmart them by **KNOWING** the material. You have a computer, you have google, you have 1 million C tutorials out there. Code, books, algorithms everything. Filter knowledge out of them.
Imagine that you were in the 60's, and your programming was done in assembler (if you were lucky) or newborn languages that hadn't matured yet. Libraries? No... Books? 1,2 ? The fact that your professor can't teach you, is no excuse. In the year 2008 using it as an excuse is like saying... "Hey i'm hungry but no-one gives me to eat" inside a restaurant full of dishes and without people.

Probably, but most lazy students will blame the teacher to avoid blaming themselves.

Originally Posted by xuftugulus

Professors rarely do teach material. Outsmart them by **KNOWING** the material. You have a computer, you have google, you have 1 million C tutorials out there. Code, books, algorithms everything. Filter knowledge out of them.
Imagine that you were in the 60's, and your programming was done in assembler (if you were lucky) or newborn languages that hadn't matured yet. Libraries? No... Books? 1,2 ? The fact that your professor can't teach you, is no excuse. In the year 2008 using it as an excuse is like saying... "Hey i'm hungry but no-one gives me to eat" inside a restaurant full of dishes and without people.

I think that's kind of cheap. If I wanted to learn C or C++ that way, I could just study it myself from home. The point of taking a class is for the teacher to help and actually teach the students and not just throw out assignments and grade. That kindof beats the whole point IMO.

Originally Posted by Elysia

The point of taking a class is for the teacher to help and actually teach the students and not just throw out assignments and grade. That kindof beats the whole point IMO.

Well, i couldn't agree more. But you must admit that education is turning a little bit towards becoming an industry on its own. Nobody is born knowing everything. My point was that usually students fail to see any worth in their tutors guidance. That is wrong, except from the fact that there are so many university teachers out there that just don't do it right. You simply can't cover 600 book pages in a semester completely. Therefore they throw out a couple of slides, and some copy paste lecture and an applicable "assignment"and consider their work done.

From the point of view of the teacher, it is usually not so easy to handle their situation better. But the student, simply can't always blame the teacher. If you are going to learn something, you'd better have your mind set to do so, instead of spitting out a blant.
"My teacher is stupid and gives us tough assignments."

This is not an appropriate thread for such discussion though, and i would prefer if we didn't prolong the subject. I just needed to clarify my point a bit, which was not meant to be insulting, but rather uprising for those that settle with cheap excuses.