Hi Dewil. I am going to give you an outline of how I would write this program, but you will need to put it together. It appears that you are fairly new to C, but you should know enough to get this going. If not, start looking through your reference book.

• Ask the user to input a string - You've already got this.
• Store the string - I would suggest using fgets for this.
• Parse the string character by character.
• If the character is valid, print it using printf("%c",*character)
• When the string is finished, print a newline printf("\n");
• Make this loop until the user types in a string that is a keyword, ie exit

I would make a seperate function that would take a char and compare it to your valid list. I would call it, is_valid and have it return a 1 if it is valid and a 0 if it is not. That way I could use it in my main loop like:


Parsing a string in C is very easy, because of the null termination, I would use a char* to parse it until it becomes NULL.


This should get you started.