doubt in strcmp

[Sameer]

Hi friends,
I am beginner in C++. I am using g++ compiler. below is my code
which gives error as " invlid conversion from 'char' to 'const char*'
..Plz help me with this.

#include <iostream.h>
#include <string.h>
int low_range(char symbol) ;

int main(int argc, char **argv)
{
char scanin ;
float range ;

float low = 0.0 ;
float high = 1.0 ;

cout << "Enter symbol\t" ;
cin >> scanin ;
while(scanin != 'Z')
{
range = high-low ;

low = low + range * low_range(scani n) ;

cout << "Value\t" ;
cin >> scanin ;

}
cout << low << endl ;
}
int rng ;
int low_range(char symbol)
{
if(strcmp(symbo l,"B")==0) //This is the line
which gives error
rng = 0.2 ;
cout << "Low range\t" << rng << endl ;
}

[Alf P. Steinbach]

* Sameer:

#include <iostream.h>
This is not a standard header; it's not available with all compilers.

Instead, use standard

#include <iostream>

#include <string.h>
int low_range(char symbol) ;

int main(int argc, char **argv)
{
char scanin ;
float range ;

float low = 0.0 ;
float high = 1.0 ;

cout << "Enter symbol\t" ;
When using standard <iostream>, you'll need to write std::cout here
(or, likely to lead to bugs, have a 'using' declaration somewhere).

cin >> scanin ;
while(scanin != 'Z')
{
range = high-low ;

low = low + range * low_range(scani n) ;

cout << "Value\t" ;
cin >> scanin ;

}
cout << low << endl ;
}
int rng ;
Don't use global variables, especially not uninitialized ones.

It seems that this was really meant as a local variable in the function
below.

int low_range(char symbol)
{
if(strcmp(symbo l,"B")==0) //This is the line which gives error
You're comparing a 'char' with a pointer to char.

Possibly you meant

if( symbol == 'B' )

rng = 0.2 ;
cout << "Low range\t" << rng << endl ;
Don't do output in a function that computes something.
}

Here you lack a 'return' statement to provide the function's result
value.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Gianni Mariani]

Sameer wrote:

Hi friends,
I am beginner in C++. I am using g++ compiler. below is my code
which gives error as " invlid conversion from 'char' to 'const char*'
.Plz help me with this.
You're comparing a C string (array of char) with a char.
int low_range(char symbol)
{
if(strcmp(symbo l,"B")==0) //This is the line

try:
if ( 'B' == symbol )

BTW - I'm not sure what your code is supposed to do so I'm not sure that
this is the intent of your code.

[Shark]

> #include <iostream.h>

#include <string.h>
these headers are deprecated. You should #include <iostream> and
#include<string > instead of the ones you have
int low_range(char symbol) ;

int main(int argc, char **argv)
{
char scanin ;
float range ;

float low = 0.0 ;
float high = 1.0 ;

cout << "Enter symbol\t" ;
small issue here: you should use std::endl instead of \t to flush the
output stream.
cin >> scanin ;
while(scanin != 'Z')
{
range = high-low ;

low = low + range * low_range(scani n) ;

cout << "Value\t" ;
cin >> scanin ;

}
cout << low << endl ;
}
int rng ;
int low_range(char symbol)
{
if(strcmp(symbo l,"B")==0) //This is the line
which gives error

Yes. basically you are trying to compare symbol which is of type char
to "B" which is a c-string. The signature of strcmp is:
int strcmp ( const char * string1, const char * string2 ); //uses two
c-style strings

The compiler wants the first argument to be of type const char*, but
the first argument you are giving it is a char. So the compiler says:
duh! you gave me a char but I need a const char*! ERROR!!!

Basically when you pass arguments to functions, the C++ compiler wants
to make sure that they are of the same type as the parameters. If they
are not, it calls the copy constructor "implicitly " (look it up,
although I may be wrong). If the copy constructor fails to do its job,
there is no solution and thereupon the compiler spits out errors.

Also, to use strcmp you need to #include<cstrin g> as it is a
c-function, not C++
hope this helps.

[Gavin Deane]

Shark wrote:

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

these headers are deprecated. You should #include <iostream> and
#include<string > instead of the ones you have

<iostream.h> is not deprecated. As far as C++ is concerned,
<iostream.h> does not exist. You are correct though that the OP wants
<iostream> instead.

But the OP's use of <string.h> is entirely correct. They are using
strcmp from the C string library which is declared in <string.h>.
<string> is the header for std::string which is completely different.
You could argue that the OP should prefer <cstring> to the deprecated
<string.h> but unfortunately I believe that many compilers do not
implement the contents of <cxxx> headers correctly so you might as well
stick with <xxx.h>

Gavin Deane

[Shark]

Gavin Deane wrote:

Shark wrote:

#include <iostream.h>
#include <string.h>
these headers are deprecated. You should #include <iostream> and
#include<string > instead of the ones you have

<iostream.h> is not deprecated. As far as C++ is concerned,
<iostream.h> does not exist. You are correct though that the OP wants
<iostream> instead.

Yes you are correct.

But code that includes iostream.h compiles none the less :) and these
headers are usually marked "deprecated " on gnu systems....so I thought
I'd use that word. :D
But the OP's use of <string.h> is entirely correct. They are using
strcmp from the C string library which is declared in <string.h>.
<string> is the header for std::string which is completely different.
You could argue that the OP should prefer <cstring> to the deprecated
<string.h> but unfortunately I believe that many compilers do not
implement the contents of <cxxx> headers correctly so you might as well
stick with <xxx.h>

hahaha. Well, I was looking at <string.h> right by <iostream.h>, so you
can't blame me for screwing up the context!

[Ian Collins]

Sameer wrote:

Hi friends,
I am beginner in C++. I am using g++ compiler. below is my code
which gives error as " invlid conversion from 'char' to 'const char*'
.Plz help me with this.

What's "Plz" ?

strcmp takes a const char* as its first parameter, you a passing a char.

Why not just use symbol == 'B'?

Ian

--
Ian Collins.

[Alf P. Steinbach]

* Shark:

But code that includes iostream.h compiles none the less :)

With some compilers.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Shark]

Alf P. Steinbach wrote:

* Shark:

But code that includes iostream.h compiles none the less :)

With some compilers.

yea, but "most" of those "some" compilers are used to compile "most" of
the code. gcc & vc
:p (ok, hasty generalization on my part)

iostream.h and like will linger on for some time.

[Alf P. Steinbach]

* Shark:

Alf P. Steinbach wrote:

* Shark:

But code that includes iostream.h compiles none the less :)

With some compilers.

yea, but "most" of those "some" compilers are used to compile "most" of
the code. gcc & vc

Note that modern versions of the vc compiler, from version 7.0 and
onwards (I think it was), do not provide <iostream.h>.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?