Loop problems

ambeco · #1 01-Mar-2004, 11:04

Most of the header files that I know how to use did not come with my compiler, so recently I have been programming some functions that do some of the same things. I need the practice anyway. This program was suppost to test a string length function, and function that finds substrings. But my loops are having lots of errors. I am using Borland 5.5 on Win XP, and if anyone can help it would be greatly appreciated. I'm going to post all the code so that you might be able to find the problem better.

CPP / C++ / C Code:

#include <iostream.h>
#include <string.h>

int substring(char *, char *);
void charins(char *, char *, int);
int len(char *);

int main()
{
	char bigstring[50];
	char littlestring[50];
             int place;
	cout << "big phrase\n";
	cin.get(bigstring, 50);
	cin.ignore(50, '\n');
	cout << "little word\n";
	cin.get(littlestring, 50);
	cin.ignore(50, '\n');
	if (substring(bigstring, littlestring))
	{cout << littlestring << " is in " << bigstring << "!!!\n";}
	else
	{cout << littlestring << " isn't in " << bigstring << ".\n";}
	cout << "place\n";
	cin >> place;
	cin.ignore(10, '\n');
	charins(bigstring, littlestring, place);
	return 0;
}

int substring(bigstring, littlestring)
{
	int loc1;
	int loc2;
	int match;
	int placeofsub
	for(loc1 = 1;loc1 == (len(bigstring) - len(littlestring)); loc1++) //six errors here
	{
		match = 1;
		for(loc2 = 1;loc2 == len(littlestring); loc2++)
		{
			if (bigstring[loc1 + loc2] != littlestring[loc2])
			{match = 0;}
		}
		if (match == 1)
		{placeofsub = loc1;}
	}
	return placeofsub;
}

void charins(bigstring, littlestring, place) //lots of errors throughout this subprogram
{
	char firsthalf[50];
	char secondhalf[50];
	int pos1;
	for (pos1 = 1;pos1 +1!= place; pos1++)
	{firsthalf[pos1] = bigstring[pos1];}
	for (pos1 = 1; pos1 + len(firsthalf) != len(bigstring); pos1++)
	{secondhalf[pos1] = bigstring[pos1+len(firsthalf)];}
	strcpy(bigstring, "");
	strcat(bigstring, firsthalf);
	strcat(bigstring, littlestring);
	strcat(bigstring, secondhalf);
}

int len(stringa)
{
	int stringlen; 
	stringlen = 0;
	while (stringa[stringlen] != '\0') // Invalid indirection here
	{stringlen++;}
	stringlen = stringlen - 1;
	return stringlen;
}

I have no idea what any of the errors mean, so please help! I think the functions are trying to use my bigstring/littlestring as integers for some reason...

WaltP · #2 01-Mar-2004, 11:55

Quote:

Originally Posted by ambeco

Most of the header files that I know how to use did not come with my compiler, so recently I have been programming some functions that do some of the same things. I need the practice anyway. This program was suppost to test a string length function, and function that finds substrings. But my loops are having lots of errors. I am using Borland 5.5 on Win XP, and if anyone can help it would be greatly appreciated. I'm going to post all the code so that you might be able to find the problem better.

What header files don't come with 5.5? I use the compiler and all standard headers are there? If you are missing standard headers, download another copy.

Quote:

Originally Posted by ambeco

I have no idea what any of the errors mean, so please help! I think the functions are trying to use my bigstring/littlestring as integers for some reason...

Neither do we since you didn't tell us what the errors were.
Two things I notice:
On the line defining placeofsub you are missing something that will cause many errors,
On the function definition above what are the parameter types?

dsmith · #3 01-Mar-2004, 12:56

Hi Ambeco.

This may not be the source of your problem but would definitely help for readability. In addition remember that you can overload functions, so instead of your function headers reading:

CPP / C++ / C Code:

int substring(bigstring, littlestring)

Change them to give the variable types as well:

CPP / C++ / C Code:

int substring(char* bigstring, char* littlestring)

I am not 100% certain, but I believe that C++ will read this as an overload function with integers instead of char*'s

davekw7x · #4 01-Mar-2004, 14:59

Well, my free version of Borland++ has all of the headers that I have
tried to use so far; where did you get yours?

I ran BCC on your program and got 15 compile errors.

Here are the first few:

Quote:

Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
s.cpp:
Warning W8054 s.cpp 30: Style of function definition is now obsolete
Error E2141 s.cpp 36: Declaration syntax error in function substring()
Error E2034 s.cpp 36: Cannot convert 'int' to 'char *' in function substring()
Error E2340 s.cpp 36: Type mismatch in parameter 1 (wanted 'char *', got 'int' ) in function substring()
Error E2034 s.cpp 36: Cannot convert 'int' to 'char *' in function substring()
Error E2340 s.cpp 36: Type mismatch in parameter 1 (wanted 'char *', got 'int ' ) in function substring()
Error E2379 s.cpp 36: Statement missing ; in function substring()

Now look at what the compiler is telling you: your line 30 is:

CPP / C++ / C Code:

int substring(bigstring, littlestring)

Since you didn't declare types of the arguments, the default behavior
of C (and, by extension of C++) is to treat them as ints. This leads
to lots of errors inside the subroutine.

change this to something like

CPP / C++ / C Code:

int substring(char bigstring[], char littlestring[])

or

CPP / C++ / C Code:

int substring(char *bigstring, char *littlestring)

Now the compiler knows that they are pointers to char.

Before you recompile with this change, note error #2379:
missing semicolon. Fix it (by adding a semicolon, naturally).

Now, use compiler messages to get a clean compile. That won't
guarantee that your program is correct, but at least you will
have something to look at to see if it's OK

OK?

Dave

ambeco · #5 02-Mar-2004, 10:55

I added the char* to the declarations and added the ; and messed with a few other things, so now it compiles. I will have to add bits of code to prevent errors but... thats a different story. In the future I will remember to include the errors. Sorry about the confusion!

ambeco · #6 02-Mar-2004, 11:36

CPP / C++ / C Code:

int substring(char * bigstring, char * littlestring)
{
	int loc1;
	int loc2;
	int match;
	int placeofsub;
	placeofsub = 0;
	for(loc1 = 1;loc1 == (len(bigstring) - len(littlestring)+1); loc1++)
	{
		match = 1;
		for(loc2 = 1;loc2 == len(littlestring); loc2++)
		{
			if (bigstring[loc1 + loc2-1] != littlestring[loc2])
			{match = 0;}
		}
		if (match == 1)
		{placeofsub = loc1;}
	}
	return placeofsub;
}

This all compiles correctly, but always says the small string isn't in the big string (returns 0) it should return the digit of the last place it was found. Anyone know why?

dsmith · #7 02-Mar-2004, 11:48

Your for statements are never being processed. You are telling your loop statement to process only when loc1 is equal to your string length which is never, because your loc1 doesn't get indexed. Use:

CPP / C++ / C Code:

for(loc2 = 1;loc2 <= len(littlestring); loc2++)

in both of your for statements.

davekw7x · #8 02-Mar-2004, 12:13

When I have programs with several new routines and the big program
doesn't give expected result, sometimes I test the individual routines
in separate programs.

For example: I think that your len() function gives the wrong answer.
(It returns a result that is 1 more than the actual string length).

Try the following:

CPP / C++ / C Code:

/* test of len() function to obtain length of a C string */
#include <stdio.h>

int main()
{

  int len(char *);

  char *s1 = "This is the first string";
  char *s2 = "Second";
  char *s3 = "";

  printf("Length of <%s> is %d\n", s1, len(s1));
  printf("Length of <%s> is %d\n", s2, len(s2));
  printf("Length of <%s> is %d\n", s3, len(s3));

  return 0;

}


int len(char *stringa)
{

  int stringlen; 

  stringlen = 0;

  while (stringa[stringlen] != '\0') {
    stringlen++;
  }
  /* stringlen = stringlen - 1; */ /* why did you do this? */
  return stringlen;

}

The first string has length = 24
The second has length = 6
The third has length = 0

(Note that your test cases should always include boundary
conditions --- i.e. make sure it's OK for all strings, including an empty
string.)

Now if you have full confidence in this function, you can concentrate
on any remaining problems.

Regards,

Dave

ambeco · #9 03-Mar-2004, 10:02

Quote:

Originally Posted by dsmith

Your for statements are never being processed. You are telling your loop statement to process only when loc1 is equal to your string length which is never, because your loc1 doesn't get indexed.

Oh right, sorry. Im still getting used to C++ from QBASIC whereyou tell it when to stop instead of when to continue. And from now on, im going to make these test programs simpler, because this WAS my simple test program. Thanks guys!

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Loop problems

Thanks Guys!

Hmmmm