Thread: invalid input

I need my program to output a message "invalid input" when the input is not correct by the user.

Currently my programs use is to allow the user to enter a number and the program outputs that number in words.

This is whats meant to happen:

Input: 30
Output: thirty
Input: 30 eight
Output: invalid input

This is what happens:

Input: 30
Output: thirty
Input 30 eight
Output: thirty

Can anyone help me with how to get the invalid input thing to work. Here is a snippet of my code:

Code:

int res;
      int num;
      res = sscanf( cmd, "%d", &num);
      switch(num){
      
      /*0 - 20*/
      
         case 0: printf("zero\n");
            break;
         case 1: printf("one\n");
            break;
         case 2: printf("two\n");
            break;
         case 3: printf("three\n");
            break;
         case 4: printf("four\n");
            break;

But theres a possibility that theres trailing chars, coz the numbers go up to 1000. I basically need to say that if a number inst entered its invalid input dont i? how do i go about doing that?

It wouldnt catch out all the invalid input by saying if theres any more chars after [3] its invalid input. How do i get it to catch it out if say the user entered: 56hj for example?

This catches the invalid input but wont print out the number now when it is valid input.

Code:

      int res;
      int num;
      int pos;
     /* res = sscanf( cmd, "%d", &num); */
      res = sscanf( cmd, "%d%n", &num, &pos);
      if ( cmd[pos] != '\n' )
         switch(num){
         
         /*0 - 20*/
         
            case 0: printf("zero\n");
               break;
            case 1: printf("one\n");
               break;
            case 2: printf("two\n");
               break;

and if i enter 7hello for example. it prints out seven.