hi everyone, hope u r all feeling fine :mrgreen:
this is my program:
#include <stdio.h>
int main()
{
char pass[12];
printf("Enter Password: ");
gets(pass);
if (pass == "neo")
{
printf ("ini");
}
else
printf("Wrong");
return 0 ;
}
when i enter "neo" as password, it does the "wrong" thing :(
how can i correct it
Jump to Posttry this:
if(strcmp(pass,"neo")==0)
printf("ini");
else
printf("Wrong");strcmp() compares two strings if strings are equal then it returns 0;
Jump to PostShalin is right, what you were comparing was the ADDRESS of pass with the ADDRESS of the quoted literal "neo". They would never be the same.
If you use std::string instead, it defines an '==' operator that does a strcmp() for you, so you may see something like this …
Jump to Posttry this............
#include <stdio.h>
#include <iostream.h>
int main()
{
char pass[12];
printf("Enter Password: ");
gets(pass);
if (pass == "neo")
cout<<"ini";
else
cout<<"Wrong";
return 0 ;
}
try this:
if(strcmp(pass,"neo")==0)
printf("ini");
else
printf("Wrong");
strcmp() compares two strings if strings are equal then it returns 0;
thanks (they told me to lengthen my message)
Shalin is right, what you were comparing was the ADDRESS of pass with the ADDRESS of the quoted literal "neo". They would never be the same.
If you use std::string instead, it defines an '==' operator that does a strcmp() for you, so you may see something like this in some code:
std::string s;
. . .
if (s == "neo")
and that WORKS because s isn't a char pointer but a class with an '==' operator defined.
try this............
#include <stdio.h>
#include <iostream.h>
int main()
{
char pass[12];
printf("Enter Password: ");
gets(pass);
if (pass == "neo")
cout<<"ini";
else
cout<<"Wrong";
return 0 ;
}
well, that, too would fail. Shalin's answer would be the simplest.
Hi everyone,
I rewrote your program a bit and seems to work for me
#include <stdio.h>
void main(void)
{
String pass;
printf("Enter Password: ");
scanf("%s",&pass);
if (pass == "neo")
{
printf ("ini");
}
else
{
printf("Wrong");
}
}
I hope this helps you
Yours Sincerely
Richard West
Hello,
It is a bad idea to use mathematical equations (==) compare strings! This is why there is a standard library to do it... strcmp is the traditional correct way to do it.
Might as well learn the proper way to do it....or that portable code may bomb out on the next compiler release.
If it is worth doing, do it correctly!
Christian
Shalin's method is the ideal one. However, if you don't want to use strcmp() for some reason, there's always a manual, lenghtier way to do it:
#include <iostream.h>
#include <stdio.h>
int main()
{
char pass[12];
char ans[4]="neo";
cout<<"Enter password: ";
gets (pass);
int flag=1, i;
for (i=0; i<4; i++)
{
if (ans[i]!=pass[i])
{
flag=0;
break;
}
}
if (flag==1)
cout<<"ini";
else
cout<<"wrong";
return 0;
}thanks to you all, really make me feel happy
How To Write Dangerous Code 101
gets (pass);string is a class:
////////////////////////////////////////////////
// file name: string
#ifndef __STRING__
#define __STRING__
#include <std/bastring.h>
extern "C++" {
typedef basic_string <char> string;
// typedef basic_string <wchar_t> wstring;
} // extern "C++"
#endif
/////////////////////////////////////////////
// file name: bastring.h
template <class charT, class traits = string_char_traits<charT>,
class Allocator = alloc >
class basic_string
{
private:
struct Rep {
size_t len, res, ref;
bool selfish;
charT* data () { return reinterpret_cast<charT *>(this + 1); }
charT& operator[] (size_t s) { return data () [s]; }
charT* grab () { if (selfish) return clone (); ++ref; return data (); }
#if defined __i486__ || defined __i586__ || defined __i686__
void release ()
{
size_t __val;
// This opcode exists as a .byte instead of as a mnemonic for the
// benefit of SCO OpenServer 5. The system assembler (which is
// essentially required on this target) can't assemble xaddl in
//COFF mode.
asm (".byte 0xf0, 0x0f, 0xc1, 0x02" // lock; xaddl %eax, (%edx)
: "=a" (__val)
: "0" (-1), "m" (ref), "d" (&ref)
: "memory");
if (__val == 1)
delete this;
}
#elif defined __sparcv9__
void release ()
{
size_t __newval, __oldval = ref;
do
{
__newval = __oldval - 1;
__asm__ ("cas [%4], %2, %0"
: "=r" (__oldval), "=m" (ref)
: "r" (__oldval), "m" (ref), "r"(&(ref)), "0" (__newval));
}
while (__newval != __oldval);
if (__oldval == 0)
delete this;
}
#else
void release () { if (--ref == 0) delete this; }
#endif
inline static void * operator new (size_t, size_t);
inline static void operator delete (void *);
inline static Rep* create (size_t);
charT* clone ();
inline void copy (size_t, const charT *, size_t);
inline void move (size_t, const charT *, size_t);
inline void set (size_t, const charT, size_t);
inline static bool excess_slop (size_t, size_t);
inline static size_t frob_size (size_t);
private:
Rep &operator= (const Rep &);
};
public:
// types:
typedef traits traits_type;
typedef typename traits::char_type value_type;
typedef Allocator allocator_type;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
typedef charT& reference;
typedef const charT& const_reference;
typedef charT* pointer;
typedef const charT* const_pointer;
typedef pointer iterator;
typedef const_pointer const_iterator;
typedef ::reverse_iterator<iterator> reverse_iterator;
typedef ::reverse_iterator<const_iterator> const_reverse_iterator;
static const size_type npos = static_cast<size_type>(-1);
private:
Rep *rep () const { return reinterpret_cast<Rep *>(dat) - 1; }
void repup (Rep *p) { rep ()->release (); dat = p->data (); }
public:
const charT* data () const
{ return rep ()->data(); }
size_type length () const
{ return rep ()->len; }
size_type size () const
{ return rep ()->len; }
size_type capacity () const
{ return rep ()->res; }
size_type max_size () const
{ return (npos - 1)/sizeof (charT); } // XXX
bool empty () const
{ return size () == 0; }
// _lib.string.cons_ construct/copy/destroy:
basic_string& operator= (const basic_string& str)
{
if (&str != this) { rep ()->release (); dat = str.rep ()->grab (); }
return *this;
}
explicit basic_string (): dat (nilRep.grab ()) { }
basic_string (const basic_string& str): dat (str.rep ()->grab ()) { }
basic_string (const basic_string& str, size_type pos, size_type n = npos)
: dat (nilRep.grab ()) { assign (str, pos, n); }
basic_string (const charT* s, size_type n)
: dat (nilRep.grab ()) { assign (s, n); }
basic_string (const charT* s)
: dat (nilRep.grab ()) { assign (s); }
basic_string (size_type n, charT c)
: dat (nilRep.grab ()) { assign (n, c); }
#ifdef __STL_MEMBER_TEMPLATES
template<class InputIterator>
basic_string(InputIterator __begin, InputIterator __end)
#else
basic_string(const_iterator __begin, const_iterator __end)
#endif
: dat (nilRep.grab ()) { assign (__begin, __end); }
~basic_string ()
{ rep ()->release (); }
void swap (basic_string &s) { charT *d = dat; dat = s.dat; s.dat = d; }
basic_string& append (const basic_string& str, size_type pos = 0,
size_type n = npos)
{ return replace (length (), 0, str, pos, n); }
basic_string& append (const charT* s, size_type n)
{ return replace (length (), 0, s, n); }
basic_string& append (const charT* s)
{ return append (s, traits::length (s)); }
basic_string& append (size_type n, charT c)
{ return replace (length (), 0, n, c); }
#ifdef __STL_MEMBER_TEMPLATES
template<class InputIterator>
basic_string& append(InputIterator first, InputIterator last)
#else
basic_string& append(const_iterator first, const_iterator last)
#endif
{ return replace (iend (), iend (), first, last); }
void push_back(charT __c)
{ append(1, __c); }
basic_string& assign (const basic_string& str, size_type pos = 0,
size_type n = npos)
{ return replace (0, npos, str, pos, n); }
basic_string& assign (const charT* s, size_type n)
{ return replace (0, npos, s, n); }
basic_string& assign (const charT* s)
{ return assign (s, traits::length (s)); }
basic_string& assign (size_type n, charT c)
{ return replace (0, npos, n, c); }
#ifdef __STL_MEMBER_TEMPLATES
template<class InputIterator>
basic_string& assign(InputIterator first, InputIterator last)
#else
basic_string& assign(const_iterator first, const_iterator last)
#endif
{ return replace (ibegin (), iend (), first, last); }
basic_string& operator= (const charT* s)
{ return assign (s); }
basic_string& operator= (charT c)
{ return assign (1, c); }
basic_string& operator+= (const basic_string& rhs)
{ return append (rhs); }
basic_string& operator+= (const charT* s)
{ return append (s); }
basic_string& operator+= (charT c)
{ return append (1, c); }
basic_string& insert (size_type pos1, const basic_string& str,
size_type pos2 = 0, size_type n = npos)
{ return replace (pos1, 0, str, pos2, n); }
basic_string& insert (size_type pos, const charT* s, size_type n)
{ return replace (pos, 0, s, n); }
basic_string& insert (size_type pos, const charT* s)
{ return insert (pos, s, traits::length (s)); }
basic_string& insert (size_type pos, size_type n, charT c)
{ return replace (pos, 0, n, c); }
iterator insert(iterator p, charT c)
{ size_type __o = p - ibegin ();
insert (p - ibegin (), 1, c); selfish ();
return ibegin () + __o; }
iterator insert(iterator p, size_type n, charT c)
{ size_type __o = p - ibegin ();
insert (p - ibegin (), n, c); selfish ();
return ibegin () + __o; }
#ifdef __STL_MEMBER_TEMPLATES
template<class InputIterator>
void insert(iterator p, InputIterator first, InputIterator last)
#else
void insert(iterator p, const_iterator first, const_iterator last)
#endif
{ replace (p, p, first, last); }
basic_string& erase (size_type pos = 0, size_type n = npos)
{ return replace (pos, n, (size_type)0, (charT)0); }
iterator erase(iterator p)
{ size_type __o = p - begin();
replace (__o, 1, (size_type)0, (charT)0); selfish ();
return ibegin() + __o; }
iterator erase(iterator f, iterator l)
{ size_type __o = f - ibegin();
replace (__o, l-f, (size_type)0, (charT)0);selfish ();
return ibegin() + __o; }
basic_string& replace (size_type pos1, size_type n1, const basic_string& str,
size_type pos2 = 0, size_type n2 = npos);
basic_string& replace (size_type pos, size_type n1, const charT* s,
size_type n2);
basic_string& replace (size_type pos, size_type n1, const charT* s)
{ return replace (pos, n1, s, traits::length (s)); }
basic_string& replace (size_type pos, size_type n1, size_type n2, charT c);
basic_string& replace (size_type pos, size_type n, charT c)
{ return replace (pos, n, 1, c); }
basic_string& replace (iterator i1, iterator i2, const basic_string& str)
{ return replace (i1 - ibegin (), i2 - i1, str); }
basic_string& replace (iterator i1, iterator i2, const charT* s, size_type n)
{ return replace (i1 - ibegin (), i2 - i1, s, n); }
basic_string& replace (iterator i1, iterator i2, const charT* s)
{ return replace (i1 - ibegin (), i2 - i1, s); }
basic_string& replace (iterator i1, iterator i2, size_type n, charT c)
{ return replace (i1 - ibegin (), i2 - i1, n, c); }
#ifdef __STL_MEMBER_TEMPLATES
template<class InputIterator>
basic_string& replace(iterator i1, iterator i2,
InputIterator j1, InputIterator j2);
#else
basic_string& replace(iterator i1, iterator i2,
const_iterator j1, const_iterator j2);
#endif
private:
static charT eos () { return traits::eos (); }
void unique () { if (rep ()->ref > 1) alloc (length (), true); }
void selfish () { unique (); rep ()->selfish = true; }
public:
charT operator[] (size_type pos) const
{
if (pos == length ())
return eos ();
return data ()[pos];
}
reference operator[] (size_type pos)
{ selfish (); return (*rep ())[pos]; }
reference at (size_type pos)
{
OUTOFRANGE (pos >= length ());
return (*this)[pos];
}
const_reference at (size_type pos) const
{
OUTOFRANGE (pos >= length ());
return data ()[pos];
}
private:
void terminate () const
{ traits::assign ((*rep ())[length ()], eos ()); }
public:
const charT* c_str () const
{ if (length () == 0) return ""; terminate (); return data (); }
void resize (size_type n, charT c);
void resize (size_type n)
{ resize (n, eos ()); }
void reserve (size_type) { }
size_type copy (charT* s, size_type n, size_type pos = 0) const;
size_type find (const basic_string& str, size_type pos = 0) const
{ return find (str.data(), pos, str.length()); }
size_type find (const charT* s, size_type pos, size_type n) const;
size_type find (const charT* s, size_type pos = 0) const
{ return find (s, pos, traits::length (s)); }
size_type find (charT c, size_type pos = 0) const;
size_type rfind (const basic_string& str, size_type pos = npos) const
{ return rfind (str.data(), pos, str.length()); }
size_type rfind (const charT* s, size_type pos, size_type n) const;
size_type rfind (const charT* s, size_type pos = npos) const
{ return rfind (s, pos, traits::length (s)); }
size_type rfind (charT c, size_type pos = npos) const;
size_type find_first_of (const basic_string& str, size_type pos = 0) const
{ return find_first_of (str.data(), pos, str.length()); }
size_type find_first_of (const charT* s, size_type pos, size_type n) const;
size_type find_first_of (const charT* s, size_type pos = 0) const
{ return find_first_of (s, pos, traits::length (s)); }
size_type find_first_of (charT c, size_type pos = 0) const
{ return find (c, pos); }
size_type find_last_of (const basic_string& str, size_type pos = npos) const
{ return find_last_of (str.data(), pos, str.length()); }
size_type find_last_of (const charT* s, size_type pos, size_type n) const;
size_type find_last_of (const charT* s, size_type pos = npos) const
{ return find_last_of (s, pos, traits::length (s)); }
size_type find_last_of (charT c, size_type pos = npos) const
{ return rfind (c, pos); }
size_type find_first_not_of (const basic_string& str, size_type pos = 0) const
{ return find_first_not_of (str.data(), pos, str.length()); }
size_type find_first_not_of (const charT* s, size_type pos, size_type n) const;
size_type find_first_not_of (const charT* s, size_type pos = 0) const
{ return find_first_not_of (s, pos, traits::length (s)); }
size_type find_first_not_of (charT c, size_type pos = 0) const;
size_type find_last_not_of (const basic_string& str, size_type pos = npos) const
{ return find_last_not_of (str.data(), pos, str.length()); }
size_type find_last_not_of (const charT* s, size_type pos, size_type n) const;
size_type find_last_not_of (const charT* s, size_type pos = npos) const
{ return find_last_not_of (s, pos, traits::length (s)); }
size_type find_last_not_of (charT c, size_type pos = npos) const;
basic_string substr (size_type pos = 0, size_type n = npos) const
{ return basic_string (*this, pos, n); }
int compare (const basic_string& str, size_type pos = 0, size_type n = npos) const;
// There is no 'strncmp' equivalent for charT pointers.
int compare (const charT* s, size_type pos, size_type n) const;
int compare (const charT* s, size_type pos = 0) const
{ return compare (s, pos, traits::length (s)); }
iterator begin () { selfish (); return &(*this)[0]; }
iterator end () { selfish (); return &(*this)[length ()]; }
private:
iterator ibegin () const { return &(*rep ())[0]; }
iterator iend () const { return &(*rep ())[length ()]; }
public:
const_iterator begin () const { return ibegin (); }
const_iterator end () const { return iend (); }
reverse_iterator rbegin() { return reverse_iterator (end ()); }
const_reverse_iterator rbegin() const
{ return const_reverse_iterator (end ()); }
reverse_iterator rend() { return reverse_iterator (begin ()); }
const_reverse_iterator rend() const
{ return const_reverse_iterator (begin ()); }
private:
void alloc (size_type size, bool save);
static size_type _find (const charT* ptr, charT c, size_type xpos, size_type len);
inline bool check_realloc (size_type s) const;
static Rep nilRep;
charT *dat;
};
template <class charT, class traits, class Allocator>
inline bool
operator== (const basic_string <charT, traits, Allocator>& lhs,
const basic_string <charT, traits, Allocator>& rhs)
{
return (lhs.compare (rhs) == 0);
}
template <class charT, class traits, class Allocator>
inline bool
operator== (const charT* lhs, const basic_string <charT, traits, Allocator>& rhs)
{
return (rhs.compare (lhs) == 0);
}
template <class charT, class traits, class Allocator>
inline bool
operator== (const basic_string <charT, traits, Allocator>& lhs, const charT* rhs)
{
return (lhs.compare (rhs) == 0);
}
Using code tags might get me to take a second look.:rolleyes:
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