C programming

I cannot get the part with saving a file to work... I got everything else... how would you implement a save file function on its own? and do that part???

nvertD Bin.c ConvertDec_to_Hex-0ct-Bin.c is a simple conversion program that prompts the user for an integer from 1 to 1,000,000, and displays this integer value in hexadecimal, octal, and binary representation. The user is then asked if the output should be saved to a text file. If user replies in the affirmative, a name for the text file is requested. If the requested text file cannot be created, user is re-prompted for a different file name. The text file will contain user's name, current date, and output results (see example below) User Interface: Enter an Integer (1 - 1000000) or type x to exit: 240 Decimal: 240 Hexadecimal: FO Octal: 360 Binary: 11110000 Save to a file? (y): y ter file name: cs222 hw3.txt File saved. Enter an Integer (1 - 1000000) or type x to exit:x Good bye! Terminal output: $cat cs222 hw3.txt Hal Greenwald Sat Oct 7 14:18:30 2017 Decimal: 240 Hexadecimal: FO Octal: 360 Binary: 11110000