User Login Verification [closed] - c++

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The program is Working perfectly fine .. but in strings if i want to restrict my username to 8 characters what should i do ? ?
cout << "Enter your Username it should have a maximum limit of 8 characters\n " << endl;
getline(cin, user, '\n');
i want here that it should restrict user for 8 characters .. if greater then 8 .. then it should keep asking
user (while loop ??)) until user enters characters less then 8 ..

Answer 1

int mystrcmp(const char *s1, const char *s2)
{
while (*s1==*s2)
{
if(*s1=='\0')
return(0);
s1++;
s2++; }
return 1;//return(*s1-*s2);
}
your int mystrcmp(const char *s1, const char *s2) was returning the difference b/w the ascii values of first non-matched chars in strings s1 and s2 and it isnt always 1 as your code supposed to.
A clean implementation of your code can be found here ideone link

Answer 2

You have a few confusions, notably between C++ strings and C strings.
Your mystrcpy function is an attempt to copy a C style string, but it's not necessary in C++. Here's how you do it in C++. Replace this
mystrcpy(new_user,user)
with this
new_user = user;
As you can see it's a bit easier to copy a C++ string than a C string. You can delete the mystrcpy function.
Similarly your mystrcmp function is an attempt to compare C strings. Again it's not necessary in C++. Replace this
f = mystrcmp(user2,new_user);
if (f==0)
{
cout << "Successful Login!! \n ";
}
with this
if (user2 == new_user)
{
cout << "Successful Login!! \n ";
}
Again you can see that comparing C++ strings is easier than comparing C strings. Again you can delete the mystrcmp function.
There a few other errors, in the logic, and some missing semi-colons, but I'll leave you do figure those out.

Answer 3

Your code is pretty much all over the place. For instance:
You need to #include <string> if you're going to use std::string.
cin >> a; if ( a == 1 ) - what if the user doesn't enter an integer at all? You'll be comparing the value of an uninitialized int to 1, which puts you in undefined behavior land. You should check the return from cin, or at a minimum initialize a.
As John mentioned, you read in std::strings, and then attempt to treat them like C strings. Don't, just use new_user = user and if ( user2 == new_user ).
If the user doesn't "Enter 1 to enter Signup Screen" you take them to the signup screen anyway.
In your mystrcmp() function, you return 0 if *s1 == '\0', but you fail to check if *s2 == '\0'. This means two things - one, if s2 is shorter than s1, then you're going out of bounds and invoking undefined behavior again, and two, if s2 is longer than s1 but begins with s1 (e.g. if s1 contains "billy" and s2 contains "billybob") then your function will say they are equal when they are not.
Also in your mystrcmp() function, this: return(*s1-*s2) will either always return 0 less the value of the element of s2 with the same index as the last index of s1, or it'll invoke undefined behavior if s2 is shorter, as already explained. Either way, it's almost certainly not something you want to return.
mystrcpy(target,source) is not a valid function definition. This function also only copies the first character of source to the first character of target.
When you loop following an incorrect entry, you check if (f == 0) and if (f == 1), but you never set f during this loop, so no matter what the user enters, you'll always just be checking what the initial result was, regardless of what they enter next.