Character Arrays Subscripting

You can absolutely loop through any array. You've passed string1 as a regular variable, and not an array. Passing an array would be either:

char MyString::strcomp(char string1[],char string2[]) // Compare using Array subscripting
...
or
...
char MyString::strcomp(char* string1,char* string2) // Compare using Array subscripting

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What you've done is assume that the string type is a null-terminated character array when it's an actual object (non-primitive).

1
2

for (unsigned i = 0; i < string1.length(); ++i) 
 cout << string1[i] << " ";

I do not recommend rcast's method of doing it because I assume you're already working with strings instead of char arrays and you don't want to cast if you don't have too.

Zaita wrote:
I do not recommend rcast's method of doing it because I assume you're already working with strings instead of char arrays and you don't want to cast if you don't have too.

The OP is passing a char not a string Zaita. He even states he is passing char arrays...

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@rcast Where does he say he is passing a char?

The error posted is a subscript error that occurs when you try to do a character comparison against a string exceeding it's length. Which occurs in this example because he has assumed a string is null-terminated.

In his post original post he is passing char string1 and char string2. I was guessing that those were C-Strings.

char MyString::strcomp(char string1,char string2) // Compare using Array subscripting

zero117 wrote:
Can you not loop through char arrays, or have I misunderstood? Welcome to any feedback

I'm pretty sure a subscript error can occur with character arrays as well. From what I know anything that is passed with data type char, is a char.

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His whole function is messed up :P

Zaita wrote:
His whole function is messed up :P

I believe the MyString::strcomp makes it a method not a function. :p :)

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Hmmm true true

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Driver file

#include <iostream>
using std::cout;
using std::endl;

#include "mystring.h"

int main()
{

   char string1[]="I am a very";
   char string2[]="good potato";
   cout<<string1[0];
   char *Ptr1=&string1[0];
   char *Ptr2=&string2[0];


    cout<<"Welcome"<<endl;

    MyString object;

    object.strcomp(*Ptr1,*Ptr1);

return 0;
}

This is in my driver program. I in no way am going to pretend I can fully keep up with arrays involving string literals and even though I have all the proper information actual usage is a bit new to me. As you can see here I was able to declare the strings in one of the accepted formats.

Class Header

#ifndef MYSTRING_H
#define MYSTRING_H
#include <iostream>
using std::cout;
using std::endl;
#include <cstring>
using std::strlen;

class MyString
{

public:

    char strcomp(char string1,char string2) ;
};

#endif // MYSTRING_H

My problem begins where I leave main and go into the function definitions as presented initially, then I can't seem to make any use of what I've passed in. I included these extra pieces of code so anyone can explain to me if I've done something wrong.

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Again let me state my unfamiliarity with these types of arrays. And moreover we were instructed to use array subscripting only for one version of each function, and pointer and pointer arithmetic for another. This is why I'm hesitant to use anything that doesn't have brackets in this particular piece.

Try this:

class MyString
{

public:

    char strcomp(char* string1,char* string2) ;
};

char MyString::strcomp(char* string1,char* string2) // Compare using Array subscripting
{
	int idx = 0;
	while (string1[idx]) {
        cout<<string1[idx];
		idx++;
	}
	return 'k';
}

int main()
{

   char string1[]="I am a very";
   char string2[]="good potato";
   char *Ptr1=string1;
   char *Ptr2=string2;

    MyString object;

    object.strcomp(Ptr1,Ptr1);

return 0;
}

You have nothing to return yet. If you will be comparing the two as the method name implies than you could return a bool if they are equal or unequal by defining the method as

bool strcomp(char* string1, char* string2) {
if (your compare found the two to be equal) {
   return true
}else{
   return false
}

or if you won't be returning anything

1
2
3

void strcomp(char* string1, char* string2) {
   ...
}

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void MyString::strcomp(char *string1,char *string2) // Compare using Array subscripting
{

for(int i=0;string1[i]!='\0';i++)// Just to test if string is passed properly
    {
        cout<<string1[i];

    }
    cout<<endl;
   int size1=strlen(string1);
   int size2=strlen(string2);

   int f;

   if(size1>size2)
   {
       f=1;
   }
   else
       if(size1<size2)
       {
           f=-1;
       }
       else if(size1==size2)
       {
           f=0;
       }

   result(f);
}

is what I ended up using. As you can see we are manually recreating the functions that can be found in <cstring> or which ever library the compiler uses.

void MyString::result(int x)
{
    if (x==-1)
    {
        cout<<"\nString 1 is less than string 2"<<endl;
    }
    else
        if(x==0)
        {
            cout<<"\nString 1 is equal to string 2"<<endl;
        }
    else
            if(x>0)
            {
                cout<<"\nString 1 is greater than string 2"<<endl;
            }

}

Is the result function the string comparison pointed to.

Again my main difficulty is just to understand what I can and can't do with pointers( ofc besides not going out of the memory address and so forth) . Can I add something into any of my arrays without erasing what was there or are their sizes definitely set? I'm asking since I didn't declare them const.

*
I obviously should change the comment on it since like the original function this one doesn't compare individual characters but rather only the size of the array. However I'll keep it for now to keep track of which function is supposed to stick to subscripts and which is to use pointer arithmetic.

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Peter87 (11178)

Zaita wrote:
What you've done is assume that the string type is a null-terminated character array when it's an actual object (non-primitive).

You can use the subscript operator with std::string almost like a normal c-string. str[str.size()] should return '\0'.

rcast wrote:
I believe the MyString::strcomp makes it a method not a function. :p :)

In C++ it's often called a member function, so calling it a function make sense.

zero117 wrote:
Can I add something into any of my arrays without erasing what was there or are their sizes definitely set? I'm asking since I didn't declare them const.

The size is fixed and can't be changed. You will find that arrays has a lot of shortcomings which will lead you to learn and love std::vector. All in good time.

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Oh, just asking because I have to recreate the connotate function. Well now I'm assuming I'll just have to create a third array to act impartially, or find some way around. And another short coming was I noticed I misunderstood the comp function. I assumed it measured array length and not individual character codes. So now I have it counting if the characters match. If the number of matches is less than the second string it'll return that first is less than the second and so forth.
*Also as you mentioned a friend already told me of the messy business with arrays.

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I've gotten much headway and thanks all for any contribution. Can I ask if anyone is familiar with how strcat works? I'm trying to recreate it here, and as said before I don't think I can change the size of string1 to include string 2, probably it uses some hidden coding. The best I've managed is to create a third array of size ( total of length of array 1 and array 2) and then place them in there ( ofc I added two extra spaces, one for a space in between and one for the null character).


void MyString::Ptrstrcat(char * string1,char * string2)
{
    int val2=strlen(string1);
    int val3=strlen(string2);
    int val1=val2+val3+2;

    char nstring[val1];
    for(int i=0;i<=val1;i++)
    {

            *(nstring+i)=*(string1+i);


    }

    *(nstring+val2)=' ';
    val2+=1;

    for(int i=0;val2<val1;val2++,i++)
    {

            *(nstring+val2)=*(string2+i);

    }
    cout<<"\nTogether both strings are: "<<nstring<<endl;

}

here is one of the functions using the code I described above ( as mentioned earlier I create two, one using regular subscripting, the other using pointer arithmetic) . Again is there anyway to overwrite the value of the first array to include both.

*Edit
Apparently I can assign the value of the new array to array1 by doing

string1=nstring;

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http://www.cplusplus.com/reference/cstring/strcat/

@rcast yes that is the function, but I'm replicating them, as per our instructions, we are to replicate the compare and concatenate functions that are in the string library. But I'm more fishing for ways how this are done. Again I'm always open to different approaches although I already have my current solution.

void MyString::strncatt(char *string1, char *string2, int d)
{
    int val1=strlen(string1);
    int fin=val1+d+2;

    char farray[fin];

    for(int i=0;i<val1;i++)
    {
        farray[i]=string1[i];
    }

    string1[val1]=' ';

    val1+=1;



    string1=farray;
    cout<<"\nString one is now: "<<string1;
}

Ok I end up running this piece of code because i noticed some odd behaviour. Apparently it automatically fills in the array by combining both of my arrays even though I didn't ask for it. Nor have I manually looped through assigning anything from the second string. Anyone have an explanation as to why this is happening? ( It's not a bad thing per se, but I'd like some closure).

*Tested my previous function doing the same and no sign of this. Is seem to automatically take on the second word from the second string. I'm not sure if this is some kind of memory error.

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