To remove one letter from a string

[jlillie89]

Hey I'm working on a function that will take a string as an input from an array. This function will go through the word letter by letter ( I suppose) and if the character at that position is something other then a letter like maybe !! or ?? or even ..... I will remove this part and return the word with the crap taken out. I'm messing around trying to write this function now. It's proving difficult. I wrote a comment where my brain passed gas.
Thanks for any ideas.

string testIt( string str1)
{	
	string newStr1 (str1.size(), ' ' ); 

	for(int i = 0; i <= str1.size(); i++)
	{	
		if(isalpha(str1[i]))
		newStr1[i]= str1[i];
		else
		str1[i]   ////// Stuck How can I erase just one character?
	
	
	
	}

}

[Lowest0ne]

use erase():
http://www.cplusplus.com/reference/string/string/erase/

[jlillie89]

I did I got a error message that is saying out of range. xthrow.cpp or something.
I don't know why it would be out of range? I read that if it is erase has just exceeded the last position but why this is on this code no idea.
Thanks

string testIt( string str1)
{	
	string newStr1  (str1.size(), ' ' ); 

	for(int i = 0; i < str1.size(); i++)
	{	
		if(isalpha(str1[i]))
		newStr1[i] = str1[i];
		else
		str1.erase(str1[i]);   
	}

	return newStr1;


}

[jlillie89]

The strange thing is that it worked once and I didn;t really change anything now nothing. I don't think this is a bad function I just can find what is wrong. It takes me to that side screen sort of this and says out of range x throw???

[Zhuge]

You don't pass the character you want to erase to erase(); just pass it's position in the string (you have it stored in 'i').

[jlillie89]

Thanks dude I haven;t ever used this function before It worked thanks:::)))))

[Zhuge]

In the future, you can look up functions like erase() on this site's reference section, giving you pages like this:
http://www.cplusplus.com/reference/string/string/erase/
It can help you figure out what parameters you need to pass and what the function does.

[vlad from moscow]

You need not to erase a character because you are coping one string into another except non-alpha characters. So in any case the target string will not contain non-alpha characters.

Your task can be done by using standard algorithm std::copy_if. For example

string newStr1;
newStr1.reserve( str1.size() );

std::copy_if( str1.begin(), str1.end(), std::back_inserter( newStr1 ),
              []( char c ) { return ( isalpha( c ) ); } );

[jlillie89]

Yeah I see what your saying. I just took out the erase part problem solved. Thanks

string testIt(string str1)
{	
	string newStr1 (str1.size(), ' ' ); 

	for(string::size_type i = 0; i < str1.size(); i++)
	{	
		if(isalpha(str1[i]))
		newStr1[i] = str1[i];
		
	}

	return newStr1;


}

[vlad from moscow]

Your code is invalid because you are returning a string with trailing spaces. I think it is not what you want to have. The result string has to have only alpha characters from the original string without any trailing spaces. So I would rewrite your code the following way

string testIt( const string &s )
{	
	string t; 
	t.reserve( s.size() ); 

	for ( string::size_type i = 0; i < s.size(); i++ )
	{	
		if ( isalpha( s[i] ) ) t.push_back( s[i] );
		
	}

	return t;
}

[jlillie89]

AHH! OK I see what you are saying the spaces are still there. But you have to explain this part of your code to me.
if ( isalpha( s[i] ) ) t.push_back( s[i] );

What exactly is push back I'm unfamiliar with this.
Thanks man

[vlad from moscow]

Well, if you did not learn push_back then you can write simply

if ( isalpha( s[i] ) ) t += s[i];

[Lowest0ne]

Push and Pop are good words to learn. To push is to add and pop is to access (often remove as well). A "push_back()" would add to the end, pop_front(), would access the beginning.