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how to use strncmp function to compare two string input by user in C++

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how to use strncmp function to compare two string input by user in C++

Jun 3rd, 2009

 Help with Code Tags 
 cpp Syntax (Toggle Plain Text) 
#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <cstring>
using namespace std;
 
 
int _tmain(int argc, _TCHAR* argv[])
{
	char s1 = "";
	char s2 = "";
	cout << "Input String1: " ;
	cin >> *s1;
	cout << "Input String2: " ;
	cin >> *s2;
 
	if ( strcmp( s1, s2 ) > 0 )
		cout << "\nThe first string is greater than the second  string." << endl;
	else if ( strcmp( s1, s2 ) == 0 )
		cout << "\nThe first string is equal to the second string." << endl;
	else if ( strcmp( s1, s2 ) < 0 )
		cout << "\nThe first string is less than the second string." <<endl;
	return 0;
}
#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <cstring>
using namespace std;


int _tmain(int argc, _TCHAR* argv[])
{
	char s1 = "";
	char s2 = "";
	cout << "Input String1: " ;
	cin >> *s1;
	cout << "Input String2: " ;
	cin >> *s2;
	
	if ( strcmp( s1, s2 ) > 0 )
		cout << "\nThe first string is greater than the second  string." << endl;
	else if ( strcmp( s1, s2 ) == 0 )
		cout << "\nThe first string is equal to the second string." << endl;
	else if ( strcmp( s1, s2 ) < 0 )
		cout << "\nThe first string is less than the second string." <<endl;
	return 0;
}

Last edited by Tekmaven; Jun 4th, 2009 at 3:27 am. Reason: Code Tags

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Re: how to use strncmp function to compare two string input by user in C++

Jun 3rd, 2009

Your use of strcmp( ) is correct.

However, your strings aren't strings. You must allocate memory for s1 and s2 as arrays of char. Or declare them as char pointers and then allocate with the new operator.

Your subject says "strncmp( )". If you want to use that variant, which compares only up till a difference or that number of characters, whichever comes first, you must add a third argument, the number of characters limit.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
if ( strcmp( s1, s2, 5 ) > 0 )  //5, for example
if ( strcmp( s1, s2, 5 ) > 0 )  //5, for example

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Re: how to use strncmp function to compare two string input by user in C++

Jun 3rd, 2009

I don't know how to input 2 string ( like, s1: csu la ece department. and s2: csu la admissom.)
And I don't know what is the right way to fix this program.

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Re: how to use strncmp function to compare two string input by user in C++

Jun 3rd, 2009

First, allocate sufficient memory for your strings. For example:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
char s1[128] = ""; //exact size depends on how big an input you expect
char s2[128] = "";
char s1[128] = ""; //exact size depends on how big an input you expect
char s2[128] = "";

Now, what you have will work, to a point. The use of cin >> s1; will limit your input to a single word. If you want to get in multi-word strings, you need to use the getline( ) method.

I'll leave it as an exercise for the reader to look up the proper usage of that - it's been amply explained here on DaniWeb, and everywhere else.

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Re: how to use strncmp function to compare two string input by user in C++

Jun 4th, 2009

Besides that you don't understand a role of stdafx.h in Visual C++. Place all standard header includes in stdafx.h (not in main module)!

Read about pre-compiled headers in Visual Studio help...

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Re: how to use strncmp function to compare two string input by user in C++

-1

Jun 4th, 2009

Dear you are declaring a char ( char s1 = "" ). Its not a string fis=rst declare a string as
char s1[10]; // string s1 of 10 characters
char s2[10]; //string s2 of 10 characters
Now take input as
cin.getline(s1,10,'\n');
cin.getlin(s2,10,'\n');
Now compare two strings. It will compile and work.
I hope you enjoy it.

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Re: how to use strncmp function to compare two string input by user in C++

Jun 4th, 2009

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Originally Posted by mirfan00

Dear you are declaring a char ( char s1 = "" ). Its not a string fis=rst declare a string as
char s1[10]; // string s1 of 10 characters
char s2[10]; //string s2 of 10 characters
Now take input as
cin.getline(s1,10,'\n');
cin.getlin(s2,10,'\n');
Now compare two strings. It will compile and work.
I hope you enjoy it.

First some remarks:

Explicitly specifying the delimiter in cin.getline(s1,10,'\n'); isn't necessary.
char s1[10]; // string s1 of 10 characters
You aren't taking the NULL-terminator '\0' into account.
cin.getline(s1,10,'\n'); : if you want this line to behave correctly then you should do one of the following:
- or, you change it to: cin.getline(s1,9,'\n');
- or you change char s1[10]; to char s1[11];

Same applies for s2

Last edited by tux4life; Jun 4th, 2009 at 3:13 pm.

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Re: how to use strncmp function to compare two string input by user in C++

Jun 4th, 2009

http://www.dinkumware.com/manuals/?m...tream::getline

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Re: how to use strncmp function to compare two string input by user in C++

Jun 4th, 2009

To tux:http://www.cplusplus.com/reference/i...tream/getline/
"Characters are extracted until either (n - 1) characters have been extracted or the delimiting character is found (which is delim if this parameter is specified, or '\n' otherwise). The extraction also stops if the end of file is reached in the input sequence or if an error occurs during the input operation"

EDIT Dave:Umm, Guess you were faster. Dani is loading real slow. I am thus using a console based browser. Sorry couldn't see you

Last edited by siddhant3s; Jun 4th, 2009 at 7:11 pm.

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Re: how to use strncmp function to compare two string input by user in C++

#10

Jun 4th, 2009

Well the objective is just to compare two strings right? Then even though strcmp can do the work wouldn't the usage as

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include<string>
using namespace std;
//within main
string str1 str2;
//inputs to strings as cin<<string
if(str1==str2)//comparision
#include<string>
using namespace std;
//within main
string str1 str2;
//inputs to strings as cin<<string
if(str1==str2)//comparision

Wouldn't the above implementation be more efficient? As we are using standard namespace.

>San you can go through this.

P.S: Guys the person "san gabriel" doesn't know about string classes I suppose may be new to c++ so wouldn't the new info be better?

Last edited by csurfer; Jun 4th, 2009 at 11:12 pm.

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