dynamic memory

[Richard]

Define a record structure to hold a set of test scores,
number of tests, and the average score. The number of
records are to be determined at runtime. Also the
number of tests for each record is to be determined at
runtime. Calculate the average test score for the set
the set of test scores in each record. Display records.
Demonstrate with a least five records. I do not know how to dynamically
allocate the number of record and the number of test scores. I can anyone
show me this first step. The rest of the program should be easy for me.
Thanks

Here is my code for dynamcally allocated number of records and test scores
in a structure.

# include <iostream>

# include <string>

using namespace std;

// structure declaration

struct student_info

{

char name[20];

int test_scores;

float average_ts;

};

// function prototypes passing structure into function





void main()

{


int student_record= 0, number_test_sco res, number_of_stude nt;


cout<<"How many student do you want to average test scores? : ";

cin >>student_recor d;

student_info student[student_record];

student_record = new int[number_of_stude nt];

cout<<"How many test scores do you want to calculate average for this
student? : ";

cin >>number_test_s cores;

}

[Eric Pruneau]

Re: dynamic memory


"Richard" <nomail1235@yah oo.com> a écrit dans le message de news:
xPKdna5seaUaKhb enZ2dnUVZ_sWdnZ 2d@comcast.com...[color=blue]
> Define a record structure to hold a set of test scores,
> number of tests, and the average score. The number of
> records are to be determined at runtime. Also the
> number of tests for each record is to be determined at
> runtime. Calculate the average test score for the set
> the set of test scores in each record. Display records.
> Demonstrate with a least five records. I do not know how to dynamically
> allocate the number of record and the number of test scores. I can anyone
> show me this first step. The rest of the program should be easy for me.
> Thanks
>
> Here is my code for dynamcally allocated number of records and test scores
> in a structure.
>
> # include <iostream>
>
> # include <string>
>
> using namespace std;
>
> // structure declaration
>
> struct student_info
>
> {
>
> char name[20];
>
> int test_scores;
>
> float average_ts;
>
> };
>[/color]

You should have an array of test_scores. Your struct should look like

struc student_info
{
char name[20]; // Personnaly I think you should use a std::string
float* test_scores; // memory will be allocated dynamically
float average_ts;
}

Note, I changed test scores type to be float instead of int...


[color=blue]
> // function prototypes passing structure into function
>
>
>
>
>
> void main()
>
> {
>
>
> int student_record= 0, number_test_sco res, number_of_stude nt;
>
>
> cout<<"How many student do you want to average test scores? : ";
>
> cin >>student_recor d;
>
> student_info student[student_record];[/color]

This is illegal... student_record must be a compile time constant for this
line to work.
you should allocate with new.

student_info* student = new student[student_record];

now you have a "dynamic array" of student_info. it can be accessed this way:
student[0], student[1], ..., student[student_record-1]
[color=blue]
> student_record = new int[number_of_stude nt];[/color]

I dont understand what you wanna do with this line but it is obvioulsy
wrong. delete that.
student_record is a plain int, not a pointer.
[color=blue]
> cout<<"How many test scores do you want to calculate average for this
> student? : ";
>
> cin >>number_test_s cores;
>
> }[/color]

Ok now that you have the number of test score, you have to allocate memory
for each student.
for(unsigned i=0; i < student_record; ++i)
student[i].test_scores = new float[number_test_sco res];

now you have a memory allocated dynamically for each student.

dont forget to delete all this memory when you are done.


Eric

[roberts.noah@gmail.com]

Re: dynamic memory


Richard wrote:[color=blue]
> Define a record structure to hold a set of test scores,
> number of tests, and the average score. The number of
> records are to be determined at runtime. Also the
> number of tests for each record is to be determined at
> runtime. Calculate the average test score for the set
> the set of test scores in each record. Display records.
> Demonstrate with a least five records. I do not know how to dynamically
> allocate the number of record and the number of test scores. I can anyone
> show me this first step. The rest of the program should be easy for me.
> Thanks
>[/color]

Eric gave a good answer. Here is one with a bit of a different spin.

I don't see any requiremnt for dynamic memory management on _your_
part. Why not use the tools at your disposal? The quoted text of the
assignment doesn't seem to require your own memory management, it just
says do this and leaves you with the task of finding a way - which will
require memory management on *somebody's* part...

#include <vector>
#include <string>

using namespace std;

struct student_info
{
string name;
vector<int> scores;
float avg;
};

Now, interestingly enough there is a data item missing in your version
that isn't in the above: the count of the scores (note the requirement
above). Since vector provides .size() it is keeping this information
for you - isn't that nice ;)

now you can do:

vector<student_ info> student_records ;

then you can...
student_info temp;
cin >> temp.name;
for (...) { int test; cin >> test; student_info.sc ores.push_back( test);
/* may as well calc avg here too */ }
student_records .push_back(temp );

Now, this is definately how I would go about solving the problem *as
given by you*. You have to decide which fits your teacher's
requirements more and use it. Good luck.