Please can someone show me how would I create a file using fstream
that would take the contents from another existing file and user input sentence.
for example:
I have file1 with some contents
The user inputs a sentence
Now I want to create a file using streams that has contents of file1 and sentence.

My possible coding

ofstream output;"file2.txt");
output<<file1 + sentence<<endl;

To me something in the code does not seem right.

How to do it depends on the contents of file1. If file1 only contains one line of text then it should be pretty simple

ifstream file1("filename.txt");
ofstream file2("outfile.txt");
string input = "Hello World";
string line;
file1 >> line;
file2 << line << input;

It becomes a little more complex when the contents of file1 is more than one line. In that case you need to use a loop to read file1 and write to file2.

Just in case you forgot. You can easily append to the end of the file.

std::string input="Hello at the end";
std::ofstream File("file1.txt",std::ios::app);
File<<input<<<std::endl;        // This is written at the end of the file.

Obviously, if you don't want to change the original, you need to make a copy, but often a simple system command will do that for you, without having to worry about writing a loop/reading/writing etc.

Thanks, I knew I was forgetting some simple command but was not sure about it.

If that solves your problem, please mark the thread as solved.
(You can always start a new one with a different problem).