I created a struct Book with the properties.I let the user to create the structure objects with for-loop.Like Books[i] Books1, Books2 etc...
The problem is that i cant store integer values in the structure.
The code is given below.
#include <stdlib.h>
#include <stdio.h>
struct Book {
int ID[];
char book_name[80];
char author_name[50];
int pblsh_date[];
};
struct Book *Books;
void Create();
int main() {
int count;
printf("How many books do you want to enter? ");
scanf("%d", &count);
Create(count);
//Show
printf("ID\t\tName\tAuthor\tPublish Year\n");
for (int i= 0; i < count; i++)
printf("%d\t%s\t%s\t%d\n", Books[i].ID, Books[i].book_name, Books[i].author_name, Books[i].pblsh_date);
if (Books) {
free(Books);
}
getchar();
return 0;
}
void Create(int count) {
Books = (struct Book*) malloc(count * sizeof(struct Book));
int i;
for (i = 0; i < count; i++) {
printf("%d. Book's ID: ", i+1);
scanf("%d", Books[i].ID);
printf("Book's name: ");
scanf("%s", Books[i].book_name);
printf("Author: ");
scanf("%s", Books[i].author_name);
printf("Publish Year: ");
scanf("%d", Books[i].pblsh_date);
}
}
The definition of the structure that you posted contains two empty arrays: int ID[]; and int pblsh_date[];. Since you did not specify a size and the compiler is not throwing an error, it is not allocating any storage for the array data: the arrays are zero-length and you are overwriting the data that follows them when you scanf into them.
Since you only want a single integer, the correct way to define the structure is
struct Book {
int ID;
char book_name[80];
char author_name[50];
int pblsh_date;
};
The only other change you need to make to your program is the arguments to scanf: scanf("%d", &(Books[i].ID)); and scanf("%d", &(Books[i].pblsh_date));. The reason is that scanf requires the address of the place you want to put the result. While scanf("%s", Books[i].book_name); works as is, you need to add the & operator to int variables. book_name is an array, which in C is treated as a pointer containing the address of the buffer you want to write to. ID is an int, so you need to get its address to know where to write to. Notice how you already did this in main with scanf("%d", &count);.
Related
Fields of Student: name, lastName, studentId, mid1Grade, mid2Grade, finalGrade, average
Fields of Course: courseName, courseCode, myStudentArray (array of Student structures),currentStudentCount
Functions:
void createNewStudent(struct Course *myCourse);
void setGradeOfStudent(struct Course *myCourse);
void findAndDisplayAverage(struct Course *myCourse);
struct Student * findStudentByID(int id, struct Course *myCourse);
void displayAverageOfAllStudents(struct Course *myCourse);
void displayAverageOfStudentsInInterval(struct Course *myCourse
ok so I have written the first function but there is an error which I dont understand. First of all the first function and what it does:
createNewStudent: Prompt the user to enter name, last name and id of the new student.Values entered by the user are assigned to the fields of the student residing in themyStudentArray of course variable pointed by myCourse. currentStudentCount will be updated so that it designates the slot allocated for the student inserted next.
and my implementation:
#include <string.h>
#include <stdio.h>
struct Student {
char name[50];
char lastname[50];
int id;
int mid1;
int mid2;
int final;
double average;
};
struct Course {
char courseName[50];
char courseCode[50];
struct Student myStudentArray[5];
int currentstudentcount;
};
void createNewStudent(struct Course * myCourse);
void setGradeOfStudent(struct Course * myCourse);
void findAndDisplayAverage(struct Course * myCourse);
struct Student * findStudentByID(int id, struct Course * myCourse);
void displayAverageOfAllStudents(struct Course * myCourse);
void displayAverageOfStudentsInInterval(struct Course * myCourse);
int main() {
struct Student * stud;
int input = 0;
scanf("%d", & input);
if (input == 1) {
createNewStudent(struct Course * myCourse);
}
}
return 0;
}
void createNewStudent(struct Course * myCourse) {
struct Student s1;
printf("Enter name: ");
scanf("%[^\n]%*c", s1.name);
printf("Enter Surname: ");
scanf("%[^\n]%*c", s1.lastname);
printf("Enter id: ");
scanf("%d", & s1.id);
}
When you call the function with the if(input == 1) it gives
error: expected expression before ‘struct’
but I dont understand this beacuse *myCourse is just a pointer to the Course struct isn't it ????
If I can understand this ı will be able to the the next functions I think
Is the function correct ?? I dont know why this doesnt work
Ok I tried to use the struct Student myStudentArray[5]; to get name, lastname,id like so (structs are the same)
void createNewStudent(struct Course *myCourse);
void setGradeOfStudent(struct Course *myCourse);
int main(){
struct Course *myCourse;
int input=0;
scanf("%d",&input);
if(input == 1){
createNewStudent(myCourse);
}
return 0;
}
void createNewStudent(struct Course *myCourse){
myCourse->currentstudentcount=0;
printf("Enter name: ");
scanf("%[^\n]%*c"
,myCourse->myStudentArray[myCourse->currentstudentcount].name);
printf("Enter Surname: ");
scanf ("%[^\n]%*c",
myCourse->myStudentArray[myCourse->currentstudentcount].name);
myCourse->currentstudentcount++;
}
I Keep getting
may be used uninitialized in this may be used uninitialized in this function [-Wmaybe-uninitialized]
and
Segmentation errors
void createNewStudent(struct Course * myCourse)
If you want to create new student, you should use the student struct as the parameter of this function instead of using struct Course.
void createNewStudent(struct Student *s1)
Then, this function becomes as:
void createNewStudent(struct Student *s1) {
printf("Enter name: ");
scanf("%49s", s1->name);
printf("Enter Surname: ");
scanf("%49s", s1->lastname);
printf("Enter id: ");
scanf("%d", & s1->id);
}
If you want to test, in main function, you can declare the value stud or the pointer to struct Student.
For example:
int main() {
struct Student stud;
int input = 0;
scanf("%d", & input);
if (input == 1) {
createNewStudent(&stud);
printf("name: %s\n Surname: %s\n id = %d\n", stud.name, stud.lastname, stud.id);
}
return 0;
}
The complete program for test:
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
struct Student {
char name[50];
char lastname[50];
int id;
int mid1;
int mid2;
int final;
double average;
};
struct Course {
char courseName[50];
char courseCode[50];
struct Student myStudentArray[5];
int currentstudentcount;
};
void createNewStudent(struct Student *s1);
int main() {
struct Student stud;
int input = 0;
scanf("%d", & input);
if (input == 1) {
createNewStudent(&stud);
printf("name: %s\nSurname: %s\nid = %d\n", stud.name, stud.lastname, stud.id);
}
return 0;
}
void createNewStudent(struct Student *s1) {
printf("Enter name: ");
scanf("%49s", s1->name);
printf("Enter Surname: ");
scanf("%49s", s1->lastname);
printf("Enter id: ");
scanf("%d", & s1->id);
}
The output:
#./test
1
Enter name: abc
Enter Surname: def
Enter id: 100
name: abc
Surname: def
id = 100
Update for your question in the comment:
If you want to store student info in an array, you can change the code to:
struct Student myStudentArray[5];
int input = 0;
scanf("%d", & input);
if (input == 1) {
for (int i = 0; i < 5; i++) {
createNewStudent(&myStudentArray[i]);
}
for (int i = 0; i < 5; i++) {
printf("name: %s\nSurname: %s\nid = %d\n", myStudentArray[i].name, myStudentArray[i].lastname, myStudentArray[i].id);
}
}
For Course structure you can create one function as the function createNewStudent but for struct Course to create the new course. After creating new 5 students (for example the code above), you can copy the myStudentArray to new_course.myStudentArray. Then now you have the info of 5 students in new_course. When you copy value from an array to another, you can use memcpy or using one loop to copy each element from one array to another one. Do not use something like myStudentArray = new_course.myStudentArray for the array.
You are making a declaration as a parameter of the createNewStudent() function. In C, functions require expressions as parameters, which is why you got the error message "expected expression...".
So, just create the struct pointer before you call the function:
if (input == 1) {
struct Course *myCourse = malloc(sizeof(struct Course));
createNewStudent(myCourse);
}
Notice the use of malloc(), which returns a pointer to a place in memory of sufficient size to hold that particular Course struct. When dealing with pointers to structs, you need to allocate memory for the structs that will ultimately be pointed to, in order to avoid dereferencing unallocated regions of memory.
In your function CerateNewStudent, the proper way to address the variables into which to place the data read by scanf should be:
myCourse->myStudentArray[myCourse->currentstudentcount].name
as the variable to read name into. Use this syntax for all data items to read. After that, increment the counter:
myCourse->currentstudentcount++;
Note: what is missing in all your functions (and in the assignment?) is a way to create a course. The students created are all added to courses. First a course should be created and then students can be added to it.
Hey guys im learning c and im currently working on stack, structure and pointer. Im using visual studio to do my the program and whenever i enter my input the program will crash. I'm able to scope down that the error is coming from the product name. I am also quite confused since it includes pointer character. Anyone can point out my mistakes? thank you
HERE ARE MY CODES
#include<stdio.h>
#include<string.h>
#define MAX 10
int top = -1;
struct Product {
int prodId;
char *prodName;
};
struct Product arrP[MAX];
struct Product pop();
void push(int id, char *name);
int isFull();
int isEmpty();
struct Product pop()
{
struct Product temp;
temp = arrP[top];
top--;
return temp;
}
void push(int id, char *name)
{
top++;
arrP[top].prodId = id;
strcpy(arrP[top].prodName,name);
}
int isFull()
{
if (top == MAX)
return 1;
else
return 0;
}
int isEmpty()
{
if (top == -1)
return 1;
else
return 0;
}
int main()
{
int myID;
char *myName;
//Push the value
printf("Enter the Product id: ");
scanf("%d", &myID);
printf("Enter the Product Name: ");
scanf("%s", &myName);
push(myID, &myName);
printf("%d %s", arrP[top].prodId ,arrP[top].prodName);
}
There are few simple bugs which you can avoid my listening to compiler warning while compiling with -Wall flag.
Case 1:- variable myId suppose to be a integer variable, not a pointer variable. If you want it to be pointer variable then you should allocate memory for it first.
int *myID;
printf("Enter the Product id: ");
scanf("%d", &myID);
Replace with
int myID;
printf("Enter the Product id: ");
scanf("%d", &myID);
Case 2:- variable myName supposed to be array of characters as you want to store product name into it.
char myName;
printf("Enter the Product Name: ");
scanf("%s", &myName);
Replace with
char myName[50];
printf("Enter the Product Name: ");
scanf("%s", myName);
While calling push() function just pass the myName. For e.g
push(myID, myName);
Also this statement
strcpy(arrP[top].prodName,name);
causes problem as prodName is pointer member in of structure, you should allocate memory dynamically for this and then do copy.
arrP[top].prodName = malloc(SIZE);
strcpy(arrP[top].prodName,name);
When you are getting the input using %s in character type variable, the memory adjacent to the address of the char variable gets overwritten thus can cause program crash. if you want to enter a string, you can try it by defining an array of characters (as char my name[MAX], MAX can be a size suitable to you).
I am getting garbage value when I display the records.
I have to create a database of students in C using array of structures and without pointers.
Is there any other way of doing this?
How to use array of structures?
#include <stdio.h>
struct student {
char first_name[10],last_name[10];
int roll;
char address[20];
float marks;
};
void accept(struct student);
void display(struct student);
void main() {
struct student S[10];
int n, i;
printf("Enter the number of records to enter : ");
scanf("%d", &n);
for (i = 0; i < n; i++) {
accept(S[i]);
}
for (i = 0; i < n; i++) {
display(S[i]);
}
}
void accept(struct student S) {
scanf("%s", S.first_name);
scanf("%s", S.last_name);
scanf("%d", &S.roll);
scanf("%s", S.address);
scanf("%f", &S.marks);
}
void display(struct student S) {
printf("\n%s", S.first_name);
printf("\n%s", S.last_name);
printf("\n%d", S.roll);
printf("\n%s", S.address);
}
Everything in C is pass-by-value. Which means you are modifying variable copy in stack frame, while real variable passed as parameter remains untouched.
You have to pass an pointer to variable which you want to modify in function.
// Function declaration
void accept(struct student *);
// Call
accept(&S[i]);
// Usage in function via dereference operator
scanf("%s",S->first_name);
If you would like to enter unknown amount of records, you should use VLA (since c99) or dynamically allocate structures.
VLA
scanf("%d",&n);
struct student S[n];
Dynamic callocation
scanf("%d",&n);
struct student * S = malloc(sizeof(struct student) * n);
Because in your case, if user input more that 9 records you are touching outside of bounds, which has undefined behavior.
There are multiple issues in your code:
The standard prototype for main without arguments is int main(void)
You should allocate the array dynamically with calloc.
you should pass structure pointers to the accept and display functions instead of passing structures by value. Passing the destination structure by value is incorrect as the accept function cannot modify the structure in the main function, which remains uninitialized and causes garbage to be displayed. Note that it is actually undefined behavior to access uninitialized data so the program could behave in even worse ways.
You should provide scanf() with the maximum number of arguments to store into character arrays to avoid potential buffer overflows.
you should verify the return values of scanf() to avoid undefined behavior on invalid input.
you could use the %[^\n] scan set to allow embedded spaces in the address field.
Here is a modified version:
#include <stdio.h>
#include <stdlib.h>
struct student {
char first_name[10], last_name[10];
int roll;
char address[20];
float marks;
};
void accept(struct student *sp);
void display(const struct student *sp);
int main(void) {
struct student *S;
int n, i, j;
printf("Enter the number of records to enter : ");
if (scanf("%d", &n) != 1)
return 1;
S = calloc(sizeof(*S), n);
if (S == NULL) {
return 1;
}
for (i = 0; i < n; i++) {
accept(&S[i]);
}
for (i = 0; i < n; i++) {
display(&S[i]);
}
free(S);
return 0;
}
void accept(struct student *sp) {
if (scanf("%9s%9s&d %19[^\n]%f",
sp->first_name, sp->last_name, &sp->roll,
sp->address, &sp->marks) != 5) {
printf("missing input\n");
exit(1);
}
}
void display(const struct student *sp) {
printf("%s\n", sp->first_name);
printf("%s\n", sp->last_name);
printf("%d\n", sp->roll);
printf("%s\n", sp->address);
printf("%f\n", sp->marks);
printf("\n");
}
I am new to programming in general and to C in particular.
I am trying to write a program that uses an array of structs, but I am experiencing problems if that struct contains strings.
Somehow the compiler crashes after the user has given the last input.
The struct below is just a simplified version containing only one item, because the problem seems to be reading strings into the array.
Any help is much appreciated, thanks in advance.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct
{
char* name;
}student;
int main()
{
int size;
printf("enter number of entries\n");
scanf("%d" , &size);
student* all=malloc(size*sizeof(student));
int i;
for(i=0;i<size;i++)
{
printf("enter name\n");
scanf("%s" , all[i].name);
}
return 0;
}
Before taking input scanf("%s" , all[i].name); , you need to allocate memory to all[i].name .
An example-
for(i=0;i<size;i++)
{
all[i].name=malloc(20*sizeof(*(all[i].name)));
if(all[i].name!=NULL){
printf("enter name\n");
scanf("%19s" , all[i].name);
}
}
//use these strings
for(i=0;i<size;i++){
free(all[i].name); //free the allocated memory
}
free(all);
Or in your structure instead of char * ,declare name as a char array (if you don't want to use dynamic allocation)-
typedef struct{
char name[20]; //give any desired size
}student;
/* no need to free in this case */
No memory is allocated for the students names (char* name), so when trying to scanf to that pointer, invalid memory is accessed and the program crashes.
The easiest way is to declare name as an array: char name[28];
The return value of malloc() needs to be checked too, in case there was problem allocating the memory for the students, which would return a NULL pointer. At the end, the allocated memory needs to be freed with free().
For example:
#include <stdio.h>
#include <stdlib.h>
typedef struct {
char name[28];
unsigned int age;
} student;
int main()
{
size_t size = 0;
printf("\nEnter number of entries: ");
scanf("%zu", &size);
// add some check for size
student* students = (student*)malloc(size * sizeof(student));
if (students == NULL) {
printf("\nProblem with allocating memory:\n"
" - size: %zu\n"
" - total size needed: %zu\n",
size, size * sizeof(student));
return 0;
}
for (size_t i = 0; i < size; ++i) {
printf("Enter name: ");
scanf("%27s", students[i].name);
printf(" Enter age: ");
scanf("%u", &students[i].age);
}
printf("\nList of students:\n");
for (size_t i = 0; i < size; ++i) {
printf("%s (%u)\n", students[i].name, students[i].age);
}
free(students); // free the allocated memory
return 0;
}
I am trying to learn about structs, pointers, and dynamic arrays in C. I don't understand how to create a dynamic array of structs using pointers. My code doesn't work, and I don't know what's wrong with it. I have seen several examples of dynamic arrays, but non with structs. Any help would be appreciated. Please give some explanation, not just code snippets as I do want to understand not just solve this problem.
#include<stdio.h>
#include<stdlib.h>
#include <string.h>
struct *struct_array;
int i,m,n,p;
struct data
{
char inputA[20];
char inputB[20];
};
struct data get_data()
{
struct data thisdata;
printf("Please enter input A\n");
scanf("%s", thisdata.inputA);
printf("Please enter input B\n");
scanf("%s", thisdata.inputB);
return thisdata;
}
void Output(struct data struct_array, int n)
{
int index = 0;
for(i = 0; i<n ;i++)
{
printf("%s ", struct_array[i].inputA);
printf("%s ", struct_array[i].inputB);
}
}
void resizeArray(int n)
{
struct_array = (int*)realloc(n*sizeof(int));
}
void mainMenu()
{
printf("Please select from the following options:\n");
printf("1: Add new students to database\n");
printf("2: Display current student database contents\n");
printf("3: exit the program\n");
scanf("%d", &p);
if(p == 1)
{
printf("Please enter the number of students to register:\n");
scanf("%d", &n);
resizeArray(n);
for(i = n; i<n ;i++)
{
struct_array[i] = get_data();
}
}
else if(p == 2)
{
Output(struct_array, n);
}
else
{
free(struct_array);
exit(0);
}
}
int main()
{
struct_array = (int*)realloc(2*sizeof(int));
mainMenu();
}
You have several errors in your source code:
struct *struct_array; (l. 5)
What does it mean? Did you want to write struct data *struct_array?
printf("%s ", struct_array[i].inputA); (l.32 & l. 33)
The argument struct_array masks the global declaration, and it is not an array. Why did you add this argument?
struct_array = (int *)realloc(n * sizeof(int)); (l. 39)
You have forgotten an argument. Did you want to use malloc instead? Besides, the cast is not necessary (and incorrect!).
Unless you are using an hosted environnment and C99/C11, you should return a value from main.
Your variable index is not used. Why did you declare it?
for(i = n; i < n; i++) (l. 53)
You won't have any iteration here...
The following code works as expected.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* TODO: Avoid global variables. */
struct data *struct_array;
struct data {
char inputA[20];
char inputB[20];
};
/*
* TODO: Try to avoid passing your structure (40 bytes + padding)
* without pointer.
*/
struct data get_data(void)
{
struct data thisdata;
printf("Please enter input A\n");
/* TODO: Avoid using `scanf` for human inputs. */
scanf("%s", thisdata.inputA);
printf("Please enter input B\n");
scanf("%s", thisdata.inputB);
return thisdata;
}
void Output(size_t n)
{
size_t i;
for (i = 0; i < n; i++) {
printf("%s ", struct_array[i].inputA);
printf("%s ", struct_array[i].inputB);
}
}
void resizeArray(size_t n)
{
/* TODO: Handle reallocations errors. */
struct_array = realloc(struct_array, n * sizeof *struct_array);
}
void mainMenu(void)
{
size_t i, n;
int p;
/* TODO: Use a loop ? */
printf("Please select from the following options:\n");
printf("1: Add new students to database\n");
printf("2: Display current student database contents\n");
printf("3: exit the program\n");
scanf("%d", &p);
switch (p) {
case 1:
printf("Please enter the number of students to register:\n");
scanf("%u", &n);
resizeArray(n);
for (i = 0; i < n; i++)
struct_array[i] = get_data();
break;
case 2:
Output(n);
break;
}
}
int main(void)
{
struct_array = malloc(2 * sizeof(int));
mainMenu();
free(struct_array);
return 0;
}
Your definition
struct *struct_array;
is erroneous. You must use the name of your type, the data.
struct data *struct_array;
This way you can allocate the array
struct_array = malloc(MaxNumElements * sizeof(struct data));
and later you should free the memory
free(struct_array);
EDIT: Type definition must occur before the var declaration.
struct data ....
struct data* your_variable;
P.S. If you do not want to type struct keyword each time you use the data type, use the typedef:
typedef struct data_s
{
char inputA[20];
char inputB[20];
} data;
Do you know how to use typedef?
I would suggest it, makes your code easier to understand and you won't have to be typing the word struct a thousand times. Also you could treat the new type similar to the primitive types (ints, chars, etc), just don't forget to use the dot (.) to access the individual fields you might want.
You could type for instance:
typedef struct{
char inputA[20];
char inputB[20];
} data;
Now you could declare variables like this:
data data_variable;
data *pointer_to_data;
And to you could allocate memory as follows:
pointer_to_data = (data*) malloc(sizeof(data)* N);
where N is the amount of struct data you want to allocate. Same works for realloc.
struct_array = (int*)realloc(2*sizeof(int));
By the above statement you are trying to assign address of an int to a pointer of type struct data.
You need to use:
struct_array = (struct data*)realloc(2*sizeof(struct data));