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InvisibleSniper

10-15-2005 03:46 AM

C Beginner Help Plz :D

Hi again,

I seem to be having a bit of trouble with some of the code I wrote. I am only new at C and this code has arrays and pointers to structures. I know what what part is wrong in it and it is the part where the user is supose to enter his/her name. I would like to store their name in an array, the reason behind the 2D array I have used is because later I will be adding more names; but I do not know what element to store the name in or even how to go about it. This code I have written is only for practic so if it doesn't make any sense to do some of the things I have done that's ok, it's just the run-time error I would like to remove, please :D

Here is my code:

Code:

#include<stdio.h>



struct employee{



int age;

char name[100][15];

};



int main()

{



struct employee *empP;







empP->age = 56;

/*

*

*Accept the user's name

*/as input.

printf("Please enter your name: ");

scanf("%[^\n]", empP->name[0][0]);





printf("The age of structure *empP is: %d", empP->age);

/*

*

*Print out the user's name

*/

printf("\nYour name is: %s",empP->name[0][0]);*/Print out the user's name*/

fflush(stdin);





getchar();





}

Thanks for your help.

jlliagre

10-15-2005 04:28 AM

1: your code has typos, fix them first (posted code should compile)
2: you are using empP without initializing it
3: compile with -Wall and fix anything gcc complains of

InvisibleSniper

10-15-2005 05:07 AM

Quote:

Originally posted by jlliagre
1: your code has typos, fix them first (posted code should compile)
2: you are using empP without initializing it
3: compile with -Wall and fix anything gcc complains of

My code compiles fine but it is a run-time error. I don't know exactly how to initialise an array yet though, I am going to go and learn now.

sind	10-15-2005 06:38 AM

Expanding on jlliagre's post, the reason why your program isn't working (I would guess that you're getting a segmentation fault / access violation) is that you haven't initialised empP, which is a pointer to a struct of type "employee".

You either need to change your declaration of empP so that it refers directly to an "employee" structure:

Code:

struct employee empP;



empP.age = 56; /* Notice the different operator to access "age" */

Or allocate memory on the free store/heap for an "employee" structure:

Code:

struct employee *empP = NULL;



/* Allocates memory for an employee struct, and puts the address

  of that memory into empP */

empP = malloc(sizeof(struct employee)); 



/* Sets each byte of the struct pointed to by empP to 0, so that it

  is in a known state */

memset(empP, 0, sizeof(struct employee));



empP->age = 56;



/* Rest of code */



/* When finished with empP, the memory should be freed */

if (empP != NULL)

{

    free(empP);

    empP = NULL;

}

Remember that a structure has to "be" somewhere for you to be able to use it. A pointer is just a variable that holds an address; you need to "make" somewhere for the struct first and tell the pointer to point to that area.

~sind

InvisibleSniper

11-02-2005 01:23 AM

Hi again,

I wanted to use some code that basically did this:

Code:



/*Check to see if the user entered any one of the data types (any one is ok)

* and if not the repeat the question to get the right type

*/

if (*hrs_worked_tdy != float || *hrs_worked_tdy != int || *hrs_worked_tdy != double)

{

//CODE BELOW

}

So in other words I want an If statement that checks to see if the variable "hrs_worked_tdy" is any of the following; an "Integer", a "Double" or a "Float". And if not then to execute the code below.

::EDIT::

I have now added this to see if it works but it still doesn't:

Code:

if (isalpha(*hrs_worked_tdy) || ispunct(*hrs_worked_tdy))

Here is my entire code:

Code:

#include<stdlib.h>

#include<stdio.h>

#include<ctype.h>

#define HOURLY_PAY 15.00

#define ONE_HOUR 60

#define PAY_OUPUT_DIR "C:\\Documents and Settings\\MasterSpotty\\My Documents\\Output_Pay.txt"



void get_user_input(float *hrs_worked_tdy)

{

for(;;)

/*No condition loop*/

{

 printf("\nPlease enter how many hours you worked today.");

 printf("\nEnter the hours you worked in the form of (1.5hrs): ");

 scanf("%f", *&hrs_worked_tdy);

 fflush(stdin);

            if (isalpha(*hrs_worked_tdy) && ispunct(*hrs_worked_tdy))

            {

            printf("\nSorry... you have entered incorrect information. Please re-enter");

            printf("\ndata and try again.");

            continue;

              }

            break;

}



}







int main()

{

FILE *wrk_fptr;

float hrs_wrked_tdy;

get_user_input(&hrs_wrked_tdy);



wrk_fptr = fopen(PAY_OUPUT_DIR, "w");

if(wrk_fptr == NULL)

{

printf("\nSorry, can not open %s. Program terminating...",PAY_OUPUT_DIR);

exit(1);

}



fprintf(wrk_fptr, "\nYou worked %2.f hours.", hrs_wrked_tdy);





fclose(wrk_fptr);



fflush(stdin);

getchar();















}

Wim Sturkenboom

11-02-2005 02:22 AM

Please indicate what the problem is. I guess it does not compile without errors / warnings.

2 things I see:

check the man page for the is.... family (isalpha etc); these functions take a char and not a number

your function get_user_input takes a pointer to hrs_worked_tdy; next, in the call to scanf you pass the address of this pointer (so pointer to pointer)

InvisibleSniper

11-03-2005 09:13 AM

It compiles and runs. All I want it to do now is check if the user entered a "grammatical character" or a "number". This is why it's like this:

Code:

if (isalpha(*hrs_worked_tdy) && ispunct(*hrs_worked_tdy))

naf	11-03-2005 04:34 PM

If you want to check for a number, use isdigit:

Code:

if( isdigit(*hrs_worked_tdy) )

If you want to check that it is only a number:

Code:

char *ptr;

double number;



for( ptr = hrs_worked_tdy; *ptr; ptr++ )

    if( ! ( isdigit( (int)( *ptr ) ) || ( *ptr == '.' ) ) )

        break;



if( *ptr ) 

    ; /* Bad number! */



number = strtod( hrs_worked_tdy, 0 );

InvisibleSniper

11-03-2005 06:58 PM

I tried using the "isdigit" function like this below:

Code:

#include<stdlib.h>

#include<stdio.h>

#include<ctype.h>

#define HOURLY_PAY 15.00

#define ONE_HOUR 60

#define PAY_OUPUT_DIR "C:\\Documents and Settings\\InvisibleSniper\\My Documents\\Output_Pay.txt"



void get_user_input(float *hrs_worked_tdy)

{

for(;;)

/*No condition loop*/

{

 printf("\nPlease enter how many hours you worked today.");

 printf("\nEnter the hours you worked in the form of (1.5hrs): ");

 scanf("%f", *&hrs_worked_tdy);

 fflush(stdin);

            if (isdigit(*hrs_worked_tdy))

            {

            printf("\nSorry... you have entered incorrect information. Please re-enter");

            printf("\ndata and try again.");

            continue;

              }

            break;

}



}







int main()

{

FILE *wrk_fptr;

float hrs_wrked_tdy;

get_user_input(&hrs_wrked_tdy);



wrk_fptr = fopen(PAY_OUPUT_DIR, "w");

if(wrk_fptr == NULL)

{

printf("\nSorry, can not open %s. Program terminating...",PAY_OUPUT_DIR);

exit(1);

}



fprintf(wrk_fptr, "\nYou worked %2.f hours.", hrs_wrked_tdy);





fclose(wrk_fptr);



fflush(stdin);

getchar();















}

But it still doesn't work, the output always evaluates to true and the body of the if statement always gets executed for some reason. Isn't there some way I could just test the isdigit function for a boolean like the following:

Code:

if(isdigit(*hrs_wrked_tdy) == 1)

/*DO

*STUFF

*/

naf	11-03-2005 11:05 PM

Well your usage there is saying "iif the first character is a digit, then complain". I don't think that is what you meant.
You want to see if the whole number is valid (all digits or period). Your if should have a ! symbol to dinicate not digiti.

Wim Sturkenboom

11-04-2005 06:42 AM

If I compile using g++ -Wall testje.c -o testje,
it tells me:

Code:

testje.c:17: warning: passing 'float' for argument passing 1 of 'int isalpha(int)'

testje.c:17: warning: argument to 'int' from 'float'

BTW, I expected the same warning as well with gcc, but that did not happen :scratch:

As stated in my earlier post, is.... functions check a character and not a float

naf	11-04-2005 07:31 AM

The problem is clear to me now. You are reading in a float and trying to see if it valid? There is no way because you just relied on scanf to do so.
However, if you read the value in as a string, validate the characters and finally convert it to a float or double, then you can do validation of non-number values. Most likely, scanf will work like strtod where invalid characters are ignored and considered the end of the value so entering "ha" = 0.

InvisibleSniper

11-04-2005 10:00 AM

Quote:

Originally posted by naf
The problem is clear to me now. You are reading in a float and trying to see if it valid? There is no way because you just relied on scanf to do so.
However, if you read the value in as a string, validate the characters and finally convert it to a float or double, then you can do validation of non-number values. Most likely, scanf will work like strtod where invalid characters are ignored and considered the end of the value so entering "ha" = 0.

Mmmm, ok thanks for that, the only problem now is that I need to make pointers to arrays if I was to use "scanf" to read the user's input into a string and then "cast" the string into a "float". And I've never made pointers to arrays :)

naf	11-04-2005 10:34 AM

I just like using doubles (better precision) instead of float personally, but you can change it to float just as well.

Code:

#include <stdlib.h>

#include <stdio.h>

#include <ctype.h>

#include <stdio.h>



#define HOURLY_PAY 15.00

#define ONE_HOUR 60

#define PAY_OUPUT_DIR "Output_Pay.txt"



void get_user_input( double *hrs_worked_tdy );



int main( int argc, char **argv )

{

        FILE *wrk_fptr;

        double hrs_wrked_tdy;



        get_user_input( &hrs_wrked_tdy );



        if( ! ( wrk_fptr = fopen( PAY_OUPUT_DIR, "wt" ) ) )

        {

                printf( "\nSorry, can not open %s. Program terminating...", PAY_OUPUT_DIR );

                exit( 1 );

        }



        fprintf( wrk_fptr, "\nYou worked %2.f hours.", hrs_wrked_tdy );



        fclose( wrk_fptr );



        fflush( stdin );

        getchar();



        return 0;

}



void get_user_input( double *hrs_worked_tdy )

{

        char buffer[128];

        char *ptr;



        /* No condition loop */

        for( ; ; )

        {

                /* Write a prompt. */

                printf( "\n"

                        "Please enter how many hours you worked today.\n" 

                        "Enter the hours you worked in the form of (1.5hrs): " );



                /* Get a line of text. */

                fgets( buffer, 128, stdin );



                /* Validate the number. */

                for( ptr = buffer; *ptr && ( *ptr != '\n' ); ptr++ )

                        if( ! ( isdigit( (int)( *ptr ) ) || ( *ptr == '.' ) ) )

                                break;        /* Value was bad. */



                /* Was valid (i.e. end reached in scan)? */

                if( *ptr == '\n' )

                {

                        *hrs_worked_tdy = strtod( buffer, 0 );

                        break;

                }



                /* Report error to user. */

                printf( "\n"

                        "Sorry... you have entered incorrect information. Please re-enter\n"

                        "data and try again." );

        } 

}

itz2000

11-05-2005 05:25 AM

Quote:

C:\\Documents and Settings\\InvisibleSniper\\My Documents\\Output_Pay.txt

WINDOWS USER ALERT!

change it to :
file:///home/user/

:]]

J/King

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