Infinite Loop when entering invalid input

**acwheat** · 04-17-2006

I'm working on a simple database. The data entry will be a combo of 5 numbers and 2 letters. If anything else other than exactly 5 numbers and 2 letters are entered an infinite loop is created. How can I filter out the bad input?

Code:

#include <stdio.h>

int main()
{
 	int num;
 	char let1, let2;
 	
 	
 	printf ("ENTER M CARD: ");
 	
 	scanf ("%d%c%c", &num, &let1, &let2);
 	

 /**************************************************/	
 if (num == 10105)
 	{if (let1 == 'B' || let1 == 'b' && let2 == 'W' || let2 == 'w')
 	       { printf ("\nM CARD IS 10105BW ");
		 printf ("\n*****************\n\n\n");
			 
			 } else
			  
			   printf ("\n INVALID ENTRY\n\n\n");
		     
 } else   
/**************************************************/ 			 
 if (num == 10106)
                {if (let1 == 'Q' || let1 == 'q' && let2 == 'C' || let2 == 'c')
 	       { printf ("\nM CARD IS 10106QC");
		 printf ("\n*****************\n\n\n");
			 
			 } else
			   
			   printf ("\n INVALID ENTRY\n\n\n");
			 
 }	else
 /***********************************************/ 
    
    printf ("\n INVALID ENTRY\n\n\n");
    

    
    
    main ();
    
    
} /******end main */

**ssharish2005** · 04-17-2006

Code:

/************************************************** */	
 if (num == 10105)
 	{if (let1 == 'B' || let1 == 'b' && let2 == 'W' || let2 == 'w')
 	       { printf ("\nM CARD IS 10105BW ");
		 printf ("\n*****************\n\n\n");
			 
			 } else
			  
			   printf ("\n INVALID ENTRY\n\n\n");
		     
 } else   
/**************************************************  */ 			 
 if (num == 10106)

moer over calling main recusively which is not good programming practice. why not use loop instead and u dont have an exit condition to exit from your recursive call of main and return value of main ??

ssharish2005

**Ideswa** · 04-17-2006

Code:

char cstring[];

// ask input, to cstring[];

// check if input is longer than 7 => infinite loop

// else,

for(int i = 7; i < 7; i++)
{
    if(i < 5)
    {
        if(isdigit(cstring[i]))
        {
            // correct
        }
        else
        {
            while....
        }
    }
    else
    {
        if(isalpha(cstring[i]))
        {
            // correct
        }
        else
        {
            while....
        }
    }
}

**Salem** · 04-18-2006

> How can I filter out the bad input?
Use fgets() to read a line of input
Use sscanf() to parse that line
Use the return result of sscanf() to determine if the input parsed correctly.

> let1 == 'B' || let1 == 'b' && let2 == 'W' || let2 == 'w'
Look up the C precedence table in your book - this does not do what you think it does.

**acwheat** · 04-18-2006

Originally Posted by Salem

>
> let1 == 'B' || let1 == 'b' && let2 == 'W' || let2 == 'w'
Look up the C precedence table in your book - this does not do what you think it does.

How about this?
((let1 == 'B' || let1 == 'b') && (let2 == 'W' || let2 == 'w'))

**dwks** · 04-18-2006

That probably does what you expect it to.

You might want to lok into tolower(), in <ctype.h>, which converts a character to lowercase.

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