How to do a case insensitive search/comparison of a string?

[MisterTams]

How can I perform a case insensitive comparison/search of a string?
I want to use cin to have the user input some string and then compare that to what is stored in an array of a string data type. The search/comparison must be case insensitive. Is there any easy way of doing this? I was searching various C++ forums and the process seemed extremely difficult (atleast to me) Haha!

Here is the function that is supposed to do this but it is obviously case sensitive in this format. :(
Please help me out!

int findStock(string *TradeName, int index)
{
	bool found = false;
	string symbol, insensitiveSymbol;
	cout << endl;
	cout << "Enter the symbol: ";
	cin >> symbol;
	
	for (int i = 0; i < index; i++)
	{
		if (symbol == TradeName[i])
		{						
			found = true;
			return i;
		}
	}

	if (found == false)
	{
		cout << "Symbol not found!" << endl;
		exit(-2); //error message, exit with an error code of -2
	}
}

Thanks,
MisterTams

[JLBorges]

#include <iostream>
#include <cctype>
#include <string>

std::string to_lower( std::string str ) // return string with all alpha characters in lower case
{
    for( char& c : str ) c = std::tolower(c) ;
    return str ;
}

// return -1 if not found
int do_find( const std::string& find_this, const std::string TradeName[], int sz )
{
    for( int i = 0 ; i < sz ; ++i )
        if( to_lower(find_this) == to_lower( TradeName[i] ) ) return i ;

    return -1 ; // not found
}

int findStock( const std::string TradeName[], int sz ) // return -1 if not found
{
    std::string symbol ;
    std::cout << "Enter the symbol: ";
	std::cin >> symbol;

    return do_find( symbol, TradeName, sz ) ;

    // this function should not be making a unilateral decision
    // to exit from the program if the item is not found
    // let the caller decide what is to be done if -1 is returned
}

[MisterTams]

JLBorges,

Thank you for your input. Is there anyway to simplify the process of insensitivity? Or is this what I should consider using? Could you explain your code a little more?

[JLBorges]

> Could you explain your code a little more?

Which is the part that you do not understand?

[MisterTams]

I don't really understand the line that has the for loop. That whole statement line 7.

[newbieg]

I'll just describe what I do, and it looks like JLBorges does pretty much the same above...

Copy your input string and the comparison string and turn the copies to lower-case. Then compare both lower-case only strings to each other. This way you don't have to worry about comparing an upper-case against a lower-case since everything is lower-case.

In line 7 JLBorges is using the std version of tolower(char) to quickly convert the string in a single-line for-each loop and then returns the copy for the comparison in line 15.

You could write your own tolower function for chars as well, but generally the c++ library has optimized code under the hood. Include the cctype library to gain access to the tolower(char) function.

Personally I would write my function to simply compare one string against another instead of testing against an entire array of strings just because it has more utility. I would leave the loop of checks against the array to either main or in this case to findStock(), but that's a personal choice.

>> JLBorges makes a very good point that the choice to exit should be dealt with in main or otherwise the calling function since in the calling function you have a bigger picture of things. Not finding the string usually isn't a reason to exit with an error code (returning a negative number is a good option since an array can't have less than 0 members). http://stackoverflow.com/questions/14109358/correct-usage-of-exit-in-c

[JLBorges]

> I don't really understand the line that has the for loop. That whole statement line 7.

for( char& c : str ) is a range based loop. http://www.stroustrup.com/C++11FAQ.html#for
It can be read as: for each character c in the string str
We use a reference char& because we want to modify the character in the body of the loop.

std::tolower(c) http://en.cppreference.com/w/cpp/string/byte/tolower
is used to convert c to a lower case character (if it is an upper case character).
c = std::tolower(c) leaves c unchanged if it is not an upper case character;
otherwise it replaces c with the equivalent lower case character.