Thread: String Validation (Newbie)

Hey Guys,

Im working on an exersise that requires the user enter a string(ID) and it must be of 4 chars long the first digit must be a char and the following 3 digits must be numeric. EG: w123

I know what I want to say but just cant get it into C.

if the user enters the string and its captured by the Var "ID"

I want to say something like:

Code:

if (ID(0)!== "a string" && ID(1)!== "a number" && ID(2)!== "a number" && ID(3)!== "a number" )
printf("The code you entered is in an incorrect format");

else

Carry on............

I realise thats probably complete jibberish heehee but I am stuck.

Thanks again in advance for any assistance.

Regards as ever
C

Hmm... do you even know how strings in C work? You might want to back up a little bit, and learn about those before you learn how to validate them.

If you do know how C strings work, then take a look at the functions isdigit() and isalpha() which are declared in ctype.h

PHP!!! colinuk you are awesome! I love PHP, you are my friend! Try something like this:

Code:

#include <ctype.h>
#include <stdio.h>

int main(void)
{
    char ID[5] = "E333";
    //get ID here

    // Validate ID
    if (!isalpha(ID[0]) || !isdigit(ID[1]) || !isdigit(ID[2]) || !isdigit(ID[3])) {
        printf("Bad format, bad!\n");
        return 1;
    }

    return 0;
}

You were close!

Hey Kleid-0

I tried what you suggested and generate an error .
The code i have is

Code:

while(check_reg==1)
{
   // Validate Reg

   if (!isalpha(record_id[0]) || !isdigit(record_id[1]) || !isdigit (record_id[2]) || !isdigit(record_id[3]))
{
   printf("Bad format, bad!\n");
   printf("Please enter an Reg No eg: w123 \n");
   scanf("%s",&record_id);
   fflush(stdin);
   check_reg = 1;
 }

   check_reg= 0;
}

The error says:
"Invalid indirection in function"

It errors out on this line:

Code:

if (!isalpha(record_id[0]) || !isdigit(record_id[1]) || !isdigit (record_id[2]) || !isdigit(record_id[3]))

Any thoughts are welcome.

Thanks again
C

colinuk: in your original post you say "!==", I think you mean "!=".

In PHP he would be comparing variable types.

Code:

int !== int  False
char !== int  True
double !== int   True
char !== char False

But that's just the thing, he's not sure how to do the same thing in C, but s/he shall learn the ways!