Thread: Structures in C

I am trying to write a program involving structures. The program must have a function that prints the first name and last name for a given student. This function has to calculate the student's average.

Then I have to have one function that computes the course's average of all the students. It doesn't appear I am doing the function call right in lines 58 and 60


I have passed the &Grades (structure)
I have tried &Grades&t

I am screwing something up. There is one example in the book but they don't pass a structure to a function. Any help is appreciated.


grades.c: In function âmainâ:
grades.c:58: error: expected expression before âGradeâ
grades.c:60: error: âsâ undeclared (first use in this function)
grades.c:60: error: (Each undeclared identifier is reported only once
grades.c:60: error: for each function it appears in.)
grades.c: At top level:
grades.c:67: error: expected identifier or â(â before â{â token
grades.c: In function âprintcourseavgâ:
grades.c:91: error: âstudentfinalâ undeclared (first use in this function)
grades.c:94: error: invalid lvalue in assignment

Code:

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

typedef  struct  Grade {
        char *firstname;
        char *lastname;
        int *grades;
} Grade; 

typedef struct Course {
        char *name;
        char *lastname;
        int *studentfinal;
} Course;

void printname ( Grade *t );

void printcourseavg ( Course *s );


int main (void){
struct Grade first;
first.firstname = "John";

struct Grade last;

last.lastname = "Doe";


struct Grade data;


data.grades = (int*) calloc(5,sizeof(int));
data.grades [ 0 ] = 78;
data.grades [ 1 ] = 87;
data.grades [ 2 ] = 85;
data.grades [ 3 ] = 86;
data.grades [ 4 ] = 85;


struct Course data1;

data1.studentfinal = (int*) calloc ( 5,sizeof (int));
data1.studentfinal [ 0 ] = 87;
data1.studentfinal [ 1 ] = 89;
data1.studentfinal [ 2 ] = 78;
data1.studentfinal [ 3 ] = 87;
data1.studentfinal [ 4 ] = 89;






printname( Grade *t);

printcourseavg(&s);

return 0;
}


void printname ( Grade *t );
{
int i;
int total;
float avg;
printf("%s\n", t->firstname);
printf("%s\n", t->lastname);

for ( i = 0; i < 4; i++ ){
        total = grades [ i ];

        }

printf("The average grade for the course is %d\n", ( float ) avg = total /4 );


}

void printcourseavg ( Course *s)  {

        int i,
        total = 0;
        float avg;

        for ( i = 0; i < 5; i++ ) {
        total = studentfinal [ i ];

        printf("The course average is %d", ( float ) avg = total / 5 );

}

Code:

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



typedef  struct  Grade {
        char *firstname;
        char *lastname;
        int *grades;
} Grade; 

typedef struct Course {
        char *name;
        char *lastname;
        int *studentfinal;
} Course;

void printname ( Grade *t);
void printcourseavg (Course *s);

int main (void){
Grade student;

student.firstname = "John";
student.lastname ="Doe";
student.grades = (int *) calloc(5,sizeof(int));
student.grades [ 0 ] = 50;
student.grades [ 1 ] = 70;
student.grades [ 2 ] = 60;
student.grades [ 3 ] = 75;
student.grades [ 4 ] = 80;


Course final;

final.studentfinal = (int*) calloc(5,sizeof(int));
final.studentfinal [ 0 ] = 78;
final.studentfinal [ 1 ] = 87;
final.studentfinal [ 2 ] = 85;
final.studentfinal [ 3 ] = 86;
final.studentfinal [ 4 ] = 85;

printname( &student);

printcourseavg(&final);

return 0;
}


void printname ( Grade *t )
{
int i;
int total = 0;
float avg;
Grade student;
printf("&#37;s\n", t->firstname);
printf("%s\n", t->lastname);  /*
student.grades = (int *) calloc(5,sizeof(int));  */
for ( i = 0; i < 4; i++ ){
        total += student.grades [ i ];

        }

printf("The average grade for the course is %f\n",  avg = total / 5 );

}

void printcourseavg ( Course *s)  {

        int i,
        total = 0;
        float avg;
        Course final;
        /*
        final.studentfinal = (int*) calloc(5,sizeof(int));*/
        for ( i = 0; i < 5; i++ ) {
        total += final.studentfinal [ i ];
        }

        printf("The course average is %f",  avg = total / 5 );

}

John
Doe
Segmentation fault

With callc in functions commented out.

John
Doe
The average grade for the course is 0.000000
The course average is 0.000000j

With calloc working in function? I don't understand why my arrays aren't getting to my functions if my John Doe is printing.

It seems to work fine, except you called this function in main

printcourseavg(&final);

and instead of using the argument, you used a local variable.
I would rewrite the function so that it uses the pointer you passed.

Free your arrays in main before the program closes, too.

Dividing by floating point numbers might help as well.

avg = total / 5.0;

Code:

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



typedef  struct  Grade {
        char *firstname;
        char *lastname;
        int *grades;
} Grade;

typedef struct Course {
        char *name;
        char *lastname;
        int *studentfinal;
} Course;

void printname ( Grade *t);
void printcourseavg (Course *s);

int main (void){

Grade student;

student.firstname = "John";
student.lastname ="Doe";
student.grades = (int *) calloc(5,sizeof(int));
student.grades [ 0 ] = 50;
student.grades [ 1 ] = 70;
student.grades [ 2 ] = 60;
student.grades [ 3 ] = 75;
student.grades [ 4 ] = 80;


Course final;

final.studentfinal = (int*) calloc(5,sizeof(int));
final.studentfinal [ 0 ] = 78;
final.studentfinal [ 1 ] = 87;
final.studentfinal [ 2 ] = 85;
final.studentfinal [ 3 ] = 86;
final.studentfinal [ 4 ] = 85;

printname( &student);

printcourseavg(&final);

return 0;
}


void printname ( Grade *t )
{
int i;
int total = 0;
int avg;

printf("&#37;s\n", t->firstname);
printf("%s\n", t->lastname);

for ( i = 0; i < 5; i++ ){
        total +=  *t->grades[i];

        }
printf("The average grade for the student is %d\n",  avg = total / 5 );


}

void printcourseavg ( Course *s)  {

        int i,
        total = 0;
        int avg;



        for ( i = 0; i < 5; i++ ) {
        total += *s ->studentfinal[i];

        }

        printf("The course average is %d",  avg = total / 5 );

}

If I do this
total += *t->grades[i];
It gives me this.
:69: error: invalid type argument of âunary *â
grades.c: In function âprintcourseavgâ:
grades.c:87: error: invalid type argument of âunary *â

if I do total += *t->grades

It will grab the first number and that's it.

However it will not divide the first number by 5 which makes no sense to me. If the total = 0 and its grabbing the first number . It should atleast divide the first number by 5 not just print the first number.

try (*t)->grades[i]

Did you do *t->firstname? Or *t->lastname? Why wouldn't you also do t->grades[i]?

Originally Posted by BSmith4740

However it will not divide the first number by 5 which makes no sense to me. If the total = 0 and its grabbing the first number . It should atleast divide the first number by 5 not just print the first number.

Except for the whole "grab the first number five times and add it up" part.

Code:

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



typedef  struct  Grade {
        char *firstname;
        char *lastname;
        int *grades;
} Grade;

typedef struct Course {
        char *name;
        char *lastname;
        int *studentfinal;
} Course;

void printname ( Grade *t);
void printcourseavg (Course *s);

int main (void){

Grade student;

student.firstname = "John";
student.lastname ="Doe";
student.grades = (int *) calloc(5,sizeof(int));
student.grades [ 0 ] = 50;
student.grades [ 1 ] = 70;
student.grades [ 2 ] = 60;
student.grades [ 3 ] = 75;
student.grades [ 4 ] = 80;


Course final;

final.studentfinal = (int*) calloc(5,sizeof(int));
final.studentfinal [ 0 ] = 78;
final.studentfinal [ 1 ] = 87;
final.studentfinal [ 2 ] = 85;
final.studentfinal [ 3 ] = 86;
final.studentfinal [ 4 ] = 85;

printname( &student);

printcourseavg(&final);

return 0;
}


void printname ( Grade *t )
{
int i;
int total = 0;
float avg;

printf("&#37;s\n", t->firstname);
printf("%s\n", t->lastname);

for ( i = 0; i < 5; i++ ){
        total +=  *t->grades;

        }

printf("The average grade for the student is %f\n",  avg = (total / 5) );
}

void printcourseavg ( Course *s)  {

        int i,
        total = 0;
        float avg;



        for ( i = 0; i < 5; i++ ) {
        total += *s ->studentfinal;

        }

        printf("The course average is %f",  avg = (total / 5) );

}

John
Doe
The average grade for the student is 50.000000
The course average is 78.000000j

My problem is I am not grabbing all the number in the for statement for some reason and I am not being able total them in the for statment

Total works for the first instant in both function but then it doesn't get divided by 5 which doesn't make sense to me.

Code:

void printname ( Grade *t )
{
int i;  
int total = 0;
float avg;

printf("%s\n", t->firstname);
printf("%s\n", t->lastname);  

for ( i = 0; i < 5; i++ ){
        total +=  (*t)->grades[i];
    
        }   

printf("The average grade for the student is %f\n",  avg = (total / 5) );

: error: invalid type argument of â->â
grades.c: In function âprintcourseavgâ:

t->firstname
t->lastname

so

t->grades[i]