Weird Runtime Error

[CJC0117]

Hi. I am using Code::Blocks 10.05 installed on my flash drive. I have a program that compiles and runs correctly on the flash drive. But when I copy and paste the program executable to the desktop, it works in some cases and not in others. Here is the code which I think might be causing the problem, although I can't figure out why:

while(true)
    {
        std::cout<<"Enter input file name (save excel sheet as a text file): ";
        getline(std::cin,line);
        if(line[line.size()-4]=='.'&&line[line.size()-3]=='t'&&line[line.size()-2]=='x'&&line[line.size()-1]=='t')
            InputFileName=line;
        else
            InputFileName=line+".txt";
        infile.open(InputFileName.c_str());
        if(!infile)
        {
            std::cout<<"\n\t\t    File does not exists.\n\n";
            infile.clear();
        }
        else
        {
            if(line[line.size()-4]=='.'&&line[line.size()-3]=='t'&&line[line.size()-2]=='x'&&line[line.size()-1]=='t')
            {
                OutputFileName=line.replace(line.size()-4,4,".csv");
                break;
            }
            else
            {
                OutputFileName=line+".csv";
                break;
            }
        }
    }

The purpose of this part of the code is to determine whether or not the user has typed a filename with the extension or not, and then choose an appropriate course of action to open the file.

Here's the problem. I have a text file called 'input' saved on the desktop. When I run the program from the desktop and type 'input.txt' when prompted for the input file name, the program runs correctly. But when I type 'input', it does not. When I enter data at a later point in the program, it prints output from one of my functions endlessly until the program crashes.

Thanks.

EDIT: When I open the .cpp file on the desktop and run the program from there, it works. It is only when I open the .exe file directly when this problem arises. I am just so confused right now.

EDIT: Also, just changing the name of the program executable gets rid of the problem...what is going on?