C++ :: File Handling Inside A While Loop?

I have two files like original.txt and replace.txt which has equal nbr of lines in both of them.

I need to loop through these two files line by line and replace the line in original.txt to the line in replace.txt

eg :

output.txt :

1|raj|65.4|Y|
1|ramesh|65.4|Y|

replace.txt :

1|raj|65.4|Y|
Cannot be processed|1|ramesh|65.4|Y|

What I need here is when reading of output.txt reaches second line of file "1|ramesh|65.4|Y|", it has to be replaced with the second line in replace.txt "Cannot be processed|1|ramesh|65.4|Y|".

1|ramesh|65.4|Y| --> Cannot be processed|1|ramesh|65.4|Y|

After the end of loop the contents of two files should be like :

original.txt :

1|raj|65.4|Y|
Cannot be processed|1|ramesh|65.4|Y|

replace.txt :

1|raj|65.4|Y|
Cannot be processed|1|ramesh|65.4|Y|

The files can have variable number of lines but both will have same number of lines each.