populate an array struct

i can populate a single struct and display it with no problem. But for some reason, when arrays get involved, I get so lost.

i want to get data for a maximum of [30] of my students and store them in an array for me to print after collecting the data.

i have done a program for one. works great. took me forever. I hava function ready to print the array.

I just need to fill it now with struct data.

help please... "point" me in the right direction.

Code:

---


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


#define MAX_STUDENTS 30
#define MAX_SIZE 48


/*Type Descriptions*/
struct student_data {
        char lastName [MAX_SIZE];
        char firstName [MAX_SIZE];
        char majCode [5];
        char yearInSchool [MAX_SIZE];
        double crHrCompl;
        double gPa;
};

/*fx prototypes*/
int get_info(struct student_data  *studentPtr);
void student_output (struct student_data students [MAX_STUDENTS], int how_many);
int how_many = 0;


int main( void )
{
        struct student_data students[MAX_STUDENTS];

        how_many = get_info (students);

        printf("student 1 name:%s\n",students[0].firstName);
        printf("student 2 name:%s\n",students[1].firstName);


        student_output (students, how_many) ;

        return 0 ;
}

/*****fx******/

int get_info(struct student_data  *studentPtr )
{
        char input_string [MAX_SIZE];
        char goAgain = 'y';
        int i = 0;
        int count = 0;

        do{

        printf("Enter Last Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->lastName, input_string, MAX_SIZE);

                studentPtr->lastName[MAX_SIZE];

        printf("Enter First Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->firstName, input_string, MAX_SIZE);

                studentPtr->firstName[MAX_SIZE];

        printf("Enter Major Code: ");
                fgets(input_string,MAX_SIZE,stdin);
               
                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->majCode, input_string, 4);
               
                studentPtr->majCode[4] = '\0';

        printf("Enter Year in School: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->yearInSchool, input_string, MAX_SIZE);

                studentPtr->yearInSchool[MAX_SIZE];

        printf("Enter Credit Hours: ");
                fgets(input_string,MAX_SIZE,stdin);

                studentPtr->crHrCompl = atof(input_string);

        printf("Enter GPA: ");
                fgets(input_string,MAX_SIZE,stdin);
       
                studentPtr->gPa = atof(input_string);
               
                i++;

                printf("Press "y" to add another, otherwise press "n" to exit. \n");
               
        scanf("%c%*c",&goAgain);
                        if (goAgain != 'y') {
                                break;       
                        }
       
        }/*do end braklet*/

                while (i != MAX_STUDENTS);

                count = i;

                return count;
}


void student_output (struct student_data students [MAX_STUDENTS], int how_many)
{
        int i = 0;

        do{
        for(i = 0; i < how_many; i++){
        printf("Last Name    : %s", students[i].lastName);
        printf("First Name    : %s", students[i].firstName);
        printf("Major Code    : %s\n", students[i].majCode);
        printf("Year in School: %s", students[i].yearInSchool);
        printf("Credit Hours  : %4.2f\n", students[i].crHrCompl);
        printf("GPA          : %4.2f\n", students[i].gPa);
       
        i++;
       
                }
        }
        while( i !=how_many);

        return;
}

---

You could do a couple of things. One is to advance the pointer at the end of the loop:

Code:

---

studentPtr+=sizeof(struct student_data);

---

Which the compiler promises to give you contiguous memory for your array, so that's okay.

The other is to use a subscript to the array ([i]) like you do in student_output. Witness that with structs, this:

Code:

---

void function (struct somestruct *ptr) {

---

*ptr could refer to a single struct, or an array. Since you have submitted an array to get_info, I believe you will have to add the subscript anyway just to get this to compile properly; the gcc error will be something like "request for member in something not a structure".

Another suggestion would be to put your questions into a char array and use another loop inside the do...while like this

Code:

---

char questions[10][32]={"Enter name: ","Enter size: ", "Enter score: "};
for (i=0;i<10;i++) {
    printf("%s",questions[i]);

---

Use a temp variable with fgets, and then a case statement to put the data you get into the right part of the struct (if you used a set of parallel arrays instead of a struct, it would be even simpler; all you would need to do is atof the last two iterations).

A couple of things --- first you never increment 'i' at the end of the do-while loop. Also, you never initialize your studentPtr. The statement
"strncpy(studentPtr->lastName, input_string, MAX_SIZE);"
points to what student?

Maybe something like "studentPtr = student_data &tempStudent"
Then it has to assign a value, doesn't it? studentPtr-> lastName = "some char[] or char* value, for example.
You never insert the student into an array!

awesome... thought so but wasn't sure where and how.

I like the additional loop idea, i'll try that for my next programs.

So i tried out the subscripts ... it feels good, but i think my loop is not working or i have the wrong loop in there. it looks right but my output is wrong.

Code:

---

/*Name of Programmer: [email protected]
  date written: 03125009
  Purpose: A programm that collects and keeps student information.
  Written for CSC_2473_290_31001
  Complied on Centrino Duo T2250 1.73GHz machine running MS Win XP and complied
    with MS Visual C++ 2008 Express

*/

#pragma warning(disable:4996) 
/*that will stop the warning on scanf being deprecated */


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


#define MAX_STUDENTS 30
#define MAX_SIZE 48


/*Type Descriptions*/
struct student_data {
        char lastName [MAX_SIZE];
        char firstName [MAX_SIZE];
        char majCode [5];
        char yearInSchool [MAX_SIZE];
        double crHrCompl;
        double gPa;
};

/*fx prototypes*/
int get_info(struct student_data students [MAX_STUDENTS]);
void student_output (struct student_data students [MAX_STUDENTS], int how_many);
int how_many = 0;


int main( void )
{
        struct student_data students[MAX_STUDENTS];

        how_many = get_info (students);

        /* printf("student 1 last name:%s\n",students[0].lastName);
        printf("student 2 last name:%s\n",students[1].lastName);*/


        student_output (students, how_many) ;

        return 0 ;
}

/*****fx******/

int get_info( struct student_data students[MAX_STUDENTS] )
{
        char input_string [MAX_SIZE];
        char goAgain = 'y';
        int i = 0;
        int count = 0;



        do{
               

        printf("Enter Last Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(students->lastName, input_string, MAX_SIZE);

                students[i].lastName[MAX_SIZE];
               

        printf("Enter First Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(students->firstName, input_string, MAX_SIZE);

                students[i].firstName[MAX_SIZE];

        printf("Enter Major Code: ");
                fgets(input_string,MAX_SIZE,stdin);
               
                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(students->majCode, input_string, 4);
               
                students[i].majCode[4] = '\0';

        printf("Enter Year in School: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(students->yearInSchool, input_string, MAX_SIZE);

                students[i].yearInSchool[MAX_SIZE];

        printf("Enter Credit Hours: ");
                fgets(input_string,MAX_SIZE,stdin);

                students[i].crHrCompl = atof(input_string);

        printf("Enter GPA: ");
                fgets(input_string,MAX_SIZE,stdin);
       
                students[i].gPa = atof(input_string);
               
                i++;

                printf("Add another? Press 'y' to add another, otherwise press n to exit. \n");
               
        scanf("%c%*c",&goAgain);
                        if (goAgain != 'y') {
                                break;       
                        }
               
        }/*doend braklet*/
       
        while(i != MAX_STUDENTS);
               

                count = i;

                return count;
}


void student_output (struct student_data students [MAX_STUDENTS], int how_many)
{
        int i = 0;

       
        for(i = 0; i < how_many; i++){
        printf("Last Name    : %s", students[i].lastName);
        printf("First Name    : %s", students[i].firstName);
        printf("Major Code    : %s\n", students[i].majCode);
        printf("Year in School: %s", students[i].yearInSchool);
        printf("Credit Hours  : %4.2f\n", students[i].crHrCompl);
        printf("GPA          : %4.2f\n", students[i].gPa);
       
        i++;
       
        if (i = how_many){
                break;
                }
        }/*for end*/
       
        return;
}

---

i enter 2 sets of data for two students and
for some reason i get only one set of data from the 2nd student entered, but with the 1st students gpa and credits.

Last Name: students[1].lastName value
First Name: students[1].firstName value
Major Code: students[1].mjaCode value
Year in school: students[1].yearInSchool value
Credits completed: students[0].crHrCompl value <--- why?
GPA : students[0].gPA value <------ why?

Code:

---

        printf("Enter Last Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(students->lastName, input_string, MAX_SIZE);

                students[i].lastName[MAX_SIZE];
               

        printf("Enter First Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(students->firstName, input_string, MAX_SIZE);

                students[i].firstName[MAX_SIZE];

        printf("Enter Year in School: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(students->yearInSchool, input_string, MAX_SIZE);

                students[i].yearInSchool[MAX_SIZE];


---

What are those lines supposed to be doing?


Quzah.

well... looks like nothing. it's been a long day.

i was trying to implement what MK27 mentioned:

Quote:

---

The other is to use a subscript to the array ([i]) like you do in student_output. Witness that with structs, this:

Code:

---


void function (struct somestruct *ptr) {

---

*ptr could refer to a single struct, or an array. Since you have submitted an array to get_info, I believe you will have to add the subscript anyway just to get this to compile properly; the gcc error will be something like "request for member in something not a structure".

---

apparently.... i didn't do it right.
my orginal idea which worked great for a single struct was:

Code:

---

int get_info(struct student_data  *studentPtr )
{
        char input_string [MAX_SIZE];
        char goAgain = 'y';
        int i = 0;
        int count = 0;

        do{

        printf("Enter Last Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->lastName, input_string, MAX_SIZE);

                studentPtr->lastName[MAX_SIZE];

ect....ect...

---

Now im trying to fill an array of student data rather than just one student data.

What's this in your for loop

Code:

---

i++;
       
        if (i = how_many){
                break;
                }
        }/*for end*/

---

The last part is redundant, since the condition was i<how_many, but i++ means that i will get incremented twice in the loop.

Here is a basic "for"

Code:

---

for (i=0;i<10;i++) {
    printf("%d\n",i);
}

---

Which will print 0-9 and then stop.

The subscripting should be here:

Code:

---

strncpy(students[i]->firstName, input_string, MAX_SIZE);

---

Those other lines you added are meaningless.

Also, since you changed the prototype:

Code:

---

int get_info(struct student_data  *studentPtr )
int get_info( struct student_data students[MAX_STUDENTS] )

---

You won't be able to use indirect notation (->); so you might as well change it back (as I said, with structs, *studentPtr could be a single struct or an array of structs, you don't need students[MAX]). The only place the subscripting is relevant is the red bit, above.

great!

this is where i was when i began. I tried to do just that but kept getting errors. I restored the original code for the day and implemented your suggestion of where to apply the subscript.

Code:

---


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


#define MAX_STUDENTS 30
#define MAX_SIZE 48


/*Type Descriptions*/
struct student_data {
        char lastName [MAX_SIZE];
        char firstName [MAX_SIZE];
        char majCode [5];
        char yearInSchool [MAX_SIZE];
        double crHrCompl;
        double gPa;
};

/*fx prototypes*/
int get_info(struct student_data  *studentPtr);
void student_output (struct student_data students [MAX_STUDENTS], int how_many);
int how_many = 0;


int main( void )
{
        struct student_data students[MAX_STUDENTS];

        how_many = get_info (students);

        printf("student 1 name:%s\n",students[0].firstName);
        printf("student 2 name:%s\n",students[1].firstName);


        student_output (students, how_many) ;

        return 0 ;
}

/*****fx******/

int get_info(struct student_data  *studentPtr )
{
        char input_string [MAX_SIZE];
        char goAgain = 'y';
        int i = 0;
        int count = 0;

        do{

        printf("Enter Last Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr[i]->lastName, input_string, MAX_SIZE);

                studentPtr->lastName[MAX_SIZE];

        printf("Enter First Name: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->firstName, input_string, MAX_SIZE);

                studentPtr->firstName[MAX_SIZE];

        printf("Enter Major Code: ");
                fgets(input_string,MAX_SIZE,stdin);
               
                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->majCode, input_string, 4);
               
                studentPtr->majCode[4] = '\0';

        printf("Enter Year in School: ");
                fgets(input_string,MAX_SIZE,stdin);

                input_string[strlen(input_string-1)] = '\0';
               
                strncpy(studentPtr->yearInSchool, input_string, MAX_SIZE);

                studentPtr->yearInSchool[MAX_SIZE];

        printf("Enter Credit Hours: ");
                fgets(input_string,MAX_SIZE,stdin);

                studentPtr->crHrCompl = atof(input_string);

        printf("Enter GPA: ");
                fgets(input_string,MAX_SIZE,stdin);
       
                studentPtr->gPa = atof(input_string);
               
                i++;

                printf("Press Enter to add another, otherwise press x to exit. \n");
               
        scanf("%c%*c",&goAgain);
                        if (goAgain != 'y') {
                                break;       
                        }
       
        }/*do end braklet*/

                while (i != MAX_STUDENTS);

                count = i;

                return count;
}


void student_output (struct student_data students [MAX_STUDENTS], int how_many)
{
        int i = 0;

        do{
        for(i = 0; i < how_many; i++){
        printf("Last Name    : %s", students[i].lastName);
        printf("First Name    : %s", students[i].firstName);
        printf("Major Code    : %s\n", students[i].majCode);
        printf("Year in School: %s", students[i].yearInSchool);
        printf("Credit Hours  : %4.2f\n", students[i].crHrCompl);
        printf("GPA          : %4.2f\n", students[i].gPa);
       
       
                }
        }
        while( i !=how_many);

        return;
}

---

ive been gettin these errors:

Code:

---

error C2232: '->lastName' : left operand has 'struct' type, use '.'
warning C4047: 'function' : 'const char *' differs in levels of indirection from 'int'
warning C4024: 'strncpy' : different types for formal and actual parameter 2
error C2198: 'strncpy' : too few arguments for call

---

...getting burned out....phew...

Quote:

---

Originally Posted by flipguy_ph

...getting burned out....phew...

---

Wow, I thought this would have been obvious but on the other hand, I did say "just there". You need to use the subscript every time you reference studentPtr. It is EXACTLY like what you do in student_output. Remember, studentPtr points to the entire array.

And I made a sort of mistake; you can't use the indirect notation anyway (don't ask me why, it seems counter-intuitive, but someone may be along to explain why); so change all those -> to dots, meaning again it is the same. So either style of prototype would amount to the same thing.

The indirect notation is for this:

Code:

---

struct this;
func(&this);
void func (struct *ptr) {
          ptr->element;
}

---

Which is passing the address of a single struct. But you are not doing that, you're passing a pointer to an array. So the syntax is the same as with chars, notice. (& with a single char, but the function prototype is the same).

you've been a great help MK27.

thanks!

i knew what you meant about "just there" not meaning "just" there. It's been a long day for a simple task. A lot of it has to do with me being at home with a 3 year old kid. my focus isn't focused.

It all works out great. and i learned some new techniques too.

cheers!

time to cook dinner. ;)