Parsing and Matching....

I some problem to solve this is our 2nd mid-term quiz in my c++ class.

this is my current code:

Code:

---

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

using namespace std;

main()
{
    char string[30];
    int x,counter,len;
    cout<<"enter string: ";
    gets(string);
    len=strlen(string);
  for (x=0; x<=len-1; x++)
    {   
        if ('string'=='(')
        {
            counter=0;
            cout<<"\ncounter: "<<counter;
            cout<<"\nValid match";
        }
        else if ('string'==')')
        {
            counter=1;
            cout<<"\ncounter: "<<counter;
            cout<<"\nInvalid match";
        }
    }       
       
   
    getch();
}

---

my instructor said that the program will only search for the '(' and ')'. if the entered string is only '(' or ')' then it is invalid match. now, it the entered string is '()' then it is a valid match. more examples is.. if the user inputs '(())' the program will count how many '(''s and how many ')'s.. then after that is subtract the number of '(' to the number of ')'... how will i gonna do these conditions??? please...

>> if ('string'=='(')
The use of 'string' there is wrong. Do you know how to get a character from the string? You are looping as if you want to loop through each character, so start by changing the 'string' to get the character at index x.

> gets(string);
eww eww eww eww - unclean!
Read the FAQ - gets() is the world's most dangerous function.

Besides, in C++, you should be using a std::string (not a char array) and a getline() method for reading input in a nice safe manner.

why should you use a std::string insted of char array in c++?

Safe, optimal and handy. Not to mention subject to the STL algorithms.

Quote:

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Originally Posted by orion-

why should you use a std::string insted of char array in c++?

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The way I had it explained to me is: a hacker can enter text that is longer than your char array's size and cin>> will happily read it all in(as long as there are no spaces). The hacker can put executable code in the text, and after it is read into memory, the code can somehow execute later. For instance, try this:

Code:

---

char str[3];
cin>>str; ///abcdefg
cout<<str[3]<<endl;

---

If you enter a string with longer than 3 characters, cin reads it in and places it memory--even though it is memory your program doesn't own. In other words, cin>> will write data past the end of the array.

>> Not to mention subject to the STL algorithms.
Actually, the standard library algorithms are generic enough to work with C style arrays just like they do with C++ containers. Of course, C++ strings are still preferred for the other reasons.