Thread: questions about character input and ignoring certain characters

hey the program that i am modding displays a letter(only the first and ignores all others) i made a minor mod on the program so that whitespaces are not read and ignored include tab spaced. i want the program so read only a-z, A-Z, or ; anything else it should just say there wasnt input
i appreciate all the advice/help i can get!

Code:

#include <stdio.h>

int skipspace(void);
int skiprest(void);

int main()
{
  int com;

        com = skipspace();  
        while (com != EOF)
        {
                printf("The command is: %c\n", com);
                skiprest();
                com = skipspace();   
        }
}

int skipspace(void)
{
  int c;

        c = getchar();
        while (c == ' ' || c == '    ') 
                c = getchar();
        return c;
}

int skiprest(void)
{
  int c;

        c = getchar();
        while (c != '\n')
                c = getchar();
        return c;
}

Code:

char legalchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

int GetLegalInput( char *allowed )
  { int ch;
     do 
      ch = getchar();
     while(! strchr(allowed,ch));
     return ch; }


// call as...
input = GetLegalInput(legalchars);

The allowed string can be any string of characters appropriate to the input you are processing.

Originally Posted by Adak

I've noticed lots of descriptions for programs, read like episode scripts from "The Twilight Zone".

Now ain't that the truth!

CommonTater thanks for the reply.
so the new code looks like this with ur function implemented
but " input = GetLegalInput(legalchars); " i dont know exactly where i should put this.

Code:

#include <stdio.h>


int skipBlanks(void);
int skipOverRestOfCommand(void);
int GetLegalInput( char *allowed );


int main()
{
  int com;
char legalchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";


        com = skipBlanks();  /* declare com */
	
        while (com != EOF)
        {
                printf("The command is: %c\n", com);
                skipOverRestOfCommand();
                com = skipBlanks();
    
        }


}


int skipBlanks(void)
{
/*
skipBlanks() ignores white spaces
*/
  int c;
        c = getchar();
	/* letters spaced or tabbed are read */
        while (c == ' ' || c == '	') 
                c = getchar();
        return c;
	


}


int skipOverRestOfCommand(void)
{
/*
skipOverRestOfCommand() skips all letters and words after the first letter entered
*/
  int c;
  
        c = getchar();
        while (c != '\n')
                c = getchar();
        return c;
}


int GetLegalInput( char *allowed )
  { int ch;
     do 
      ch = getchar();
     while(! strchr(allowed,ch));
     return ch; }

I thought Tater would be back, but OK.

You can delete your other code selection functions, and just use Tater's function ( as a separate function, not in main() ). Just have the return from it, go into your char array[]. Say you want 5 legal letters:

Code:

for(i=0;i<5;i++) {
   myCharArray[i] = GetLegalInput(allowed);
}

And myCharArray[] will end up with 5 legal char's.

SkipBlanks and SkipOverRest you can delete.

This is why scoop and poop coding is a REAL BAD IDEA... you wind up with all this stuff on your page and you don't even know how any of it works...

You've dropped that code into your source and you don't even call it...
Not only that but you don't need skipoverblanks or skiprest anymore since those characters are consumed in the GetLegalInput function.

What the OP needs to do is to stop borrowing code and actually sit down with a textbook and learn C programming.

that makes more sense but i havent used arrays or i dont even know how to use them but i have tidy the program a bit and here is what i ended up with

Code:

#include <stdio.h>

int GetLegalInput( char *allowed );

int main()
{
  int cmd;

        cmd = GetLegalInput();
        while (cmd != EOF)
        {
                printf("The command is: %c\n", cmd);
        
    
        }
}

int GetLegalInput( char *allowed )
  { 
int ch, i;
char legalchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    for(i=0; i<51;i++)
    {
        Char[i] = GetLegalInput(allowed);
     do
      ch = getchar();
     while( strchr(allowed,ch));
     return ch; 
  }

Originally Posted by Adak

I thought Tater would be back, but OK.

You can delete your other code selection functions, and just use Tater's function ( as a separate function, not in main() ). Just have the return from it, go into your char array[]. Say you want 5 legal letters:

Code:

for(i=0;i<5;i++) {
   myCharArray[i] = GetLegalInput(allowed);
}

And myCharArray[] will end up with 5 legal char's.

SkipBlanks and SkipOverRest you can delete.

Originally Posted by ecsx00

that makes more sense but i havent used arrays or i dont even know how to use them but i have tidy the program a bit and here is what i ended up with

Code:

#include <stdio.h>

int GetLegalInput( char *allowed );

int main()
{
  int cmd;

        cmd = GetLegalInput();
        while (cmd != EOF)
        {
                printf("The command is: %c\n", cmd);
        
    
        }
}

int GetLegalInput( char *allowed )
  { 
int ch, i;
char legalchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    for(i=0; i<51;i++)
    {
        Char[i] = GetLegalInput(allowed);
     do
      ch = getchar();
     while( strchr(allowed,ch));
     return ch; 
  }

nope... still not going to work... In fact I doubt it would compile...
Your cmd != EOF ain't happening because it's not on the legal characters list and will not be returned by the function.
As soon as you enter 1 keystroke the program is going into an infinite loop.

Code:

#include <stdio.h>
#include <string.h>

int GetLegalInput( char *allowed )
  { int ch;
     do 
      ch = getchar();
     while(! strchr(allowed,ch));
     return ch; }


int main (void)
  { 
     char *legalchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!";
     int cmd;
     
     do 
        {  cmd = GetLegalInput(legalchars);
            printf ("Command = %c\n", cmd); }
     while (cmd != '!');

     return 0; 
}

CommonTater, thanks man now I have an idea how the function works. ill come back in a few hours if i cant get a print statement to show up but thanks for the big help!

Originally Posted by CommonTater

nope... still not going to work... In fact I doubt it would compile...
Your cmd != EOF ain't happening because it's not on the legal characters list and will not be returned by the function.
As soon as you enter 1 keystroke the program is going into an infinite loop.

Code:

#include <stdio.h>
#include <string.h>

int GetLegalInput( char *allowed )
  { int ch;
     do 
      ch = getchar();
     while(! strchr(allowed,ch));
     return ch; }


int main (void)
  { 
     char *legalchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!";
     int cmd;
     
     do 
        {  cmd = GetLegalInput(legalchars);
            printf ("Command = %c\n", cmd); }
     while (cmd != '!');

     return 0; 
}

Now do yourself a favour... and don't just copy what I wrote... use the principles I showed you and write a version of the code that works best in your situation. Copy and paste... Scoop and poop usually leaves you with poop!

My point is simply this: You need to learn C Programming... not Code Theft.

(sorry if that's blunt, but it's true)

CommonTater yea thanks for the tip/info. i am right now remaking and tweaking the code to get it to do what i want it to do overall.
the only thing is if lets say i enter an "illegal" character i want an error message to display the mod code is below

tweaked code a little bit with an added nonworking print statement

Code:

#include <string.h>
#include <stdio.h>

int main (void)
{
char *legalchars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
int cmd, flag;

do
{ cmd = GetLegalInput(legalchars);
printf ("Command = %c\n", cmd); }
while (flag != EOF);

do
{ cmd != GetLegalInput(legalchars);
printf("Error: %c is not a letter\n", cmd);
}
while (cmd != GetLegalInput(legalchars));
}


int GetLegalInput( char *allowed )
{ int ch, flag;
do
flag = ch = getchar();
while(! strchr(allowed,ch));
return ch; 
}