Write a c/c program that executes the command "ls" with standard output redirected to a file "a. txt". the same program then asks the user to enter a search key (using cin), reads the a. txt file to find it and reports whether the search key was found among the list of files in the current directory or not. note that you must use an exec() function to run the "ls" command and before that, you must redirect stdout to the file a. txt. also, at the end, you must report the result in the stdout. you cannot use the "system()" function. make sure to test your program.