Automatically rename a file if it already exists in Windows way

Question

My C# code is generating several text files based on input and saving those in a folder. Also, I am assuming that the name of the text file will be same as input.(The input

Answer 1

int count= 0;

file is the name of file

while (File.Exists(fullpathwithfilename))  //this will check for existence of file
{ 
// below line names new file from file.xls to file1.xls   
fullpathwithfilename= fullpathwithfilename.Replace("file.xls", "file"+count+".xls"); 

count++;
}