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program with padding a string.

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Join Date: Feb 2009

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halfnode

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program with padding a string.

Feb 18th, 2009

hi all pretty new to programming here

the idea of the code is for the function to take in an string and an int and to pad the string with space on the left with the int being the number of space to put in.

am i doing something wrong?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <string>
using namespace std;
 
string padBlanks(string, int);
 
int main()
{
string string1;
int padN;
 
cout<< "Please enter a string";
cin>> string1;
cout<< "Please enter a number";
cin >> padN;
 
padBlanks(string1, padN);
 
cin.ignore();
cin.ignore();
}
 
string padBlanks(string string1, int padN)
{
string blank(padN,' ');
 
cout<< blank <<string1;
return 0;
}
#include <iostream>
#include <string>
using namespace std;

string padBlanks(string, int);

int main()
{
string string1;
int padN;

cout<< "Please enter a string";
cin>> string1;
cout<< "Please enter a number";
cin >> padN;

padBlanks(string1, padN);

cin.ignore();
cin.ignore();
}

string padBlanks(string string1, int padN)
{
string blank(padN,' ');

cout<< blank <<string1;
return 0;
}

i keep getting the error Expression invalid null pointer

"The program '[3180] test.exe: Native' has exited with code 3 (0x3)."

thanks for the help!

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Join Date: Nov 2008

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StuXYZ

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Re: program with padding a string.

Feb 18th, 2009

First off, well done for using code tags for your first post.

Second, your error is that you are returning 0 but actually need to return a string.
Try as the last two lines of padBlanks, this:

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c++ Syntax (Toggle Plain Text)

blank+=string1;
return blank;

experience is the most expensive way to learn anything

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dmanw100

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Re: program with padding a string.

Feb 18th, 2009

You need to put the return 0; at the end of your main() function. The padBlanks() function will return the string.

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Join Date: Jul 2008

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ArkM

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Re: program with padding a string.

Feb 18th, 2009

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
if (padN > 0)
    string1.insert(0,padN,' ');
if (padN > 0)
    string1.insert(0,padN,' ');

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kbshibukumar kbshibukumar is offline

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Re: program with padding a string.

Feb 19th, 2009

The problem is that when your function is returning a string, it first makes a copy of the string to be returned (in your case, it is NULL). For making copy, it has to take the length of the original string. Of course, strlen(NULL) fails.
You can make your string return a reference as
const string& PadBlanks(string string1, int padN)
Then the copy is no longer made. However, the variable pad should be globally accessible.

Regards,
Shibu
http://cppkid.wordpress.com

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Join Date: Feb 2009

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halfnode

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Re: program with padding a string.

Feb 20th, 2009

hey thanks for the help all. got it solved =)

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Join Date: Feb 2009

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halfnode

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Re: program with padding a string.

Feb 21st, 2009

i just found a bug with the coding. it doesn't accept a string with space in it such as test test. the spacing throws an error
Microsoft C++ exception: std::bad_alloc at memory location 0x0012f50c.

any advice?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
 
string padBlanks(string, int);//function header
void removeLetter(string& inStr, char);
 
int main()
{
string string1;
int padN;
string inStr;
char alpha;
 
cout<< "Please enter a string"<<endl;
cin>> string1;
cout<< "Please enter a number"<<endl;
cin >> padN;
 
padBlanks(string1, padN);
 
cout<< "Please enter a sentence"<<endl;
cin>> inStr;
cout<< "Please enter a char to be removed"<<endl;
cin >> alpha;
 
cout<<"This is the string before function call "<<inStr <<endl;
removeLetter(inStr, alpha);
 
cin.ignore();
cin.ignore();
}
 
string padBlanks(string string1, int padN)//function body
{
 
	string blank(padN,' ');
 
cout<< blank <<string1<<endl;
return blank;
}
 
void removeLetter(string& inStr, char alpha ) 
{  
 
			//replace(inStr.begin(),inStr.end(),alpha," ");
//	remove(inStr.begin(), inStr.end(),alpha);
int i;
for ( i = 0; i < inStr.length(); i++)
if (inStr.at(i) == alpha)
{
	inStr.erase(i,1);
 	i--;
}
	cout<<"This is the string after function call "<< inStr <<endl;
}
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

string padBlanks(string, int);//function header
void removeLetter(string& inStr, char);

int main()
{
string string1;
int padN;
string inStr;
char alpha;

cout<< "Please enter a string"<<endl;
cin>> string1;
cout<< "Please enter a number"<<endl;
cin >> padN;

padBlanks(string1, padN);

cout<< "Please enter a sentence"<<endl;
cin>> inStr;
cout<< "Please enter a char to be removed"<<endl;
cin >> alpha;

cout<<"This is the string before function call "<<inStr <<endl;
removeLetter(inStr, alpha);

cin.ignore();
cin.ignore();
}

string padBlanks(string string1, int padN)//function body
{

	string blank(padN,' ');

cout<< blank <<string1<<endl;
return blank;
}

void removeLetter(string& inStr, char alpha ) 
{  

			//replace(inStr.begin(),inStr.end(),alpha," ");
//	remove(inStr.begin(), inStr.end(),alpha);
int i;
for ( i = 0; i < inStr.length(); i++)
if (inStr.at(i) == alpha)
{
	inStr.erase(i,1);
 	i--;
}
	cout<<"This is the string after function call "<< inStr <<endl;
}

Last edited by halfnode; Feb 21st, 2009 at 10:21 pm.

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Join Date: Jul 2008

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ArkM

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Re: program with padding a string.

Feb 22nd, 2009

>i just found a bug with the coding.
Alas, you did not found a bug in this unpleasant, untidy code

Next time use code tag properly:
[code=c++]
codes...
[/code]

Well, cin >> string1 gets a single word only, not a line (see operator>> for std::string specification). For example, after the string1<Enter> the string1 value is "the" and the next input statement gets "string1". However the next input cin >> padN wants an integer but "string1" is not an integer and the cin input stream is in failed state now. No value for padN variable, it has undefined value after failed input. Probably, the program catch an exception when was trying to padd a huge or negative number of blanks...

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
getline(cin,string1); // get a whole line
cout<< "Please enter a number" << endl; // What's a number?
if (cin >> padN) { // OK, test padBlanks
    ....
} else { // bad input
    cout << "*** It's not a number" << endl;
    cin.clear(); // clear cin state
    cin.ignore(1000,'\n'); // skip bad input
}
... go on ...
getline(cin,string1); // get a whole line
cout<< "Please enter a number" << endl; // What's a number?
if (cin >> padN) { // OK, test padBlanks
    ....
} else { // bad input
    cout << "*** It's not a number" << endl;
    cin.clear(); // clear cin state
    cin.ignore(1000,'\n'); // skip bad input
}
... go on ...

Of course, the padBlanks function presented is a forged surrogate only. Have you ever seen my previous post? There is true padBlanks function body in the snippet.