Question

My goal is to produce a program that will take a file as input and “encode” the text within by shifting the characters ahead 3 (so ‘a’ would be come ‘d’). It should produce an output file with the encoded text. The menu is to take user input and execute the function that is assigned to the number selected.

I’m early on at creating this program, but running short on time and am struggling with how to structure it. Currently, I have the menu displaying, but when a sub function is called, it displays but then the menu overwrites it and I can’t figure out why. Any help would be appreciated. Here is the code I have so far…

#include <stdio.h>
#define INPUT_FILE 1    //define statements
#define OUTPUT_FILE 2
#define NUM_TO_SHIFT 3
#define ENCODE 4
#define QUIT 0

int menu();     //function prototypes
int input();
int output();
int shift();
int encode();
void quit();

int main()
{
    int choice;     // main variables
    char user_filename[100];

    choice = menu();   // get user's first selection

    while(choice != QUIT)   //execute so long as choice is not equal to QUIT
    {
        switch(choice)
            {
                case INPUT_FILE:
                    printf("Enter the filename of the file to encode:\n");
                    printf("(hit the Enter key when done)\n");
                    gets(user_filename);
                    break;
                case OUTPUT_FILE: output();
                    break;
                case NUM_TO_SHIFT: shift();
                    break;
                case ENCODE: encode();
                    break;
                case QUIT: quit();
                    break;
                default:    printf("Oops! An invalid choice slipped through. ");
                            printf("Please try again.\n");
            }
      choice = menu(); /* get user's subsequent selections */
   }

   printf("Bye bye!\n");
   return 0;
}

int menu(void)
{
    int option;

    printf("Text Encoder Service\n\n");
    printf("1.\tEnter name of input file (currently 'Secret.txt')\n");
    printf("2.\tEnter name of output file (currently not set)\n");
    printf("3.\tEnter number of characters data should be shifted (currently +7)\n");
    printf("4.\tEncode the text\n\n");
    printf("0.\tQuit\n\n");
    printf("Make your selection: ");

    while( (scanf(" %d", &option) != 1) /* non-numeric input */
          || (option < 0)               /* number too small */
          || (option > 4))              /* number too large */
    {
      fflush(stdin);                    /* clear bad data from buffer */
      printf("That selection isn't valid. Please try again.\n\n");
      printf("Your choice? ");
    }
    return option;
}

int input()
{

}

int output()
{
    return 2;
}

int shift()
{
    return 3;
}

int encode()
{
    return 4;
}

void quit()
{
    printf("Quiting...Bye!");
    exit(0);
}

Answer 1

You shouldn’t use gets(user_filename) to get the file name since gets() reads up to a \n and stops reading. Your scanf for the menu option does not read the \n at the end of the line when the user types in the menu option. Essentially, you’re making gets read a string without words in it. The line you want to read is actually the next line. Using scanf instead of gets will fix it.

Otherwise, your program is working as expected – it’s just that your functions don’t do anything yet that your menu is “overwriting” the submenus. See http://ideone.com/F2pEs for an implementation with scanf instead of gets.