C program - skipping user input - c

I created a program that uses arrays and array pointers to store a user's animal name, category of animal, and age. But when I run it, there is a segmentation fault after I type the name age and category. I was wondering if someone could guide me in how to fix it, I am very new to C programming.
This is the task I am supposed to complete:
Write a program that defines an animal data type, with an animal name, age, and category (cat, dog, etc.), as well as an animal array type that stores an array of animal pointers.  Your program will prompt the user to enter the data for as many animals as they wish.  It will initialize a dynamically allocated animal structure for each animal, and it will store each animal in an instance of the animal array structure.  Your program will then print all the animal information to the screen.  You will upload your C program as one file.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct {
char *name;
char *category;
int age;
} AnimalType;
typedef struct {
AnimalType basicInfo;
AnimalType *arr[];
} AnimalArrayType;
void initAnimal(char *n, char *c, int a, AnimalArrayType *ar);
void printAnimal(const AnimalArrayType *stuPtr);
int main() {
AnimalArrayType *array;
int numAn;
char name[20];
char category[20];
int age;
printf("Please enter the number of animals you want to input: ");
scanf("%d", &numAn);
array = calloc(numAn, sizeof(AnimalArrayType));
for (int i=0; i<numAn; ++i) {
printf("Enter animal name: ");
scanf("%s", name);
printf("Enter their category: ");
scanf("%s", category);
printf("Enter age: ");
scanf("%d", &age);
initAnimal(name, category, age, array + I);
}
printf("\n LIST:\n");
for (int i=0; i<numAn; ++i) {
printAnimal(array + I);
}
return 0;
}
void initAnimal(char *n, char *c, int a, AnimalArrayType *ar)
{
strcpy(ar->basicInfo.name, n);
strcpy(ar->basicInfo.category, c);
ar->basicInfo.age = a;
}
void printAnimal(const AnimalArrayType *stuPtr)
{
printf("Animal: %s, Category: %s age %d\n",
stuPtr->basicInfo.name, stuPtr->basicInfo.category,
stuPtr->basicInfo.age);
}

The char *name and char *category fields in the AnimalType struct are being initialized to NULL (from the call to calloc()), but you don't allocate any char[] memory for them to point at afterwards, so you end up crashing in initAnimal() when it tries to copy data into those fields using strcpy().
You need to either:
change those fields into char[] arrays instead of char* pointers:
typedef struct {
char name[20];
char category[20];
int age;
} AnimalType;
allocate memory for them to point at, such as from strdup():
typedef struct {
char *name;
char *category;
int age;
} AnimalType;
...
void initAnimal(char *n, char *c, int a, AnimalArrayType *ar)
{
ar->basicInfo.name = strdup(n);
ar->basicInfo.category = strdup(c);
ar->basicInfo.age = a;
}
Don't forget to free() anything you dynamically allocate when you are done using it.

Related

Structure function pointer parameter?

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.

using strtok in C to assign value to a structure

i am receiving a default char array (first/last) in guest_init (and i need to initialize the values such that guest have default values ) is my following code correct? as when i run this g->first_name is always being assigned garbage. need some help.
struct guest {
char last_name[30];
char first_name[30];
};
struct auditorium_seating {
struct guest **seating;
};
void guest_init_default(struct guest *g)
{
*g->first_name = "???";
*g->last_name = "???";
}
void guest_init(struct guest *g, char *info)
{
strcpy(g->first_name, strtok(info, "/"));
strcpy(g->last_name, strtok(NULL, "\0"));
}
void auditorium_seating_init(int rowNum, int columnNum, struct auditorium_seating *a)
{
a->seating=malloc((sizeof(a->seating[rowNum][columnNum])));
char string_arr[30]="aaa/bbb";
for (int i = 0; i<rowNum; i++)
{
for (int j = 0; j<columnNum; j++)
{
//guest_init_default(a->seating);
guest_init(a->seating,string_arr);
}
}
}
auditorium_seating_init being called from main.
void main() {
struct auditorium_seating auditorium_seating;
struct guest temp_guest;
int row, col, rowNum, columnNum;
char guest_info[30];
printf("Please enter a number of rows for an auditorium seating.");
scanf_s("%d", &rowNum);
printf("Please enter a number of columns for an auditorium seating.");
scanf_s("%d", &columnNum);
auditorium_seating_init(rowNum, columnNum, &auditorium_seating);
printf("Please enter a guest information or enter \"Q\" to quit.");
}
Enable your compiler warnings: *g->first_name = "???"; is wrong.
And strtok(NULL, "\0")); is wrong too.
You probably want this:
#include <string.h>
#include <stdio.h>
struct guest {
char last_name[30];
char first_name[30];
};
void guest_init(struct guest *g, char *info)
{
strcpy(g->first_name, strtok(info, "/"));
strcpy(g->last_name, strtok(NULL, "/"));
}
int main()
{
struct guest g;
char info[] = "Foo/Bar";
guest_init(&g, info);
printf("Last Name = %s\n", g.last_name);
printf("First Name = %s\n", g.first_name);
}
There may be more errors related to struct auditorium_seating *a, but you didn't post that code.
No, you must copy data to your structure, as you allocated memory inside it.
Read compiler errors and use it to fix your program.

Array of structs in c: giving all the strings same values (with the int it works well). What sould I do?

When I run the program and give values to the id, name, surname it gives them all the value of the last student. For instance if the last students name is Anna then all the other names of the array are Anna. With the grades it works well! I tried and without the 'constructor' function and happenden the same thing.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Student{ /*struct for student info*/
char *id;
char *name;
char *surname;
int grade;
};
struct Student* Student_new(char* id, char* name, char* surname, int grade);
/*fuction: Student 'constructor'*/
int main(int argc, char *argv[]) {
int no; /*number of students*/
printf("Welcome! \n\nNumber of students: ");
scanf("%d", &no);
struct Student *studentArray[no]; /*arary of struct students*/
int i; /*counter*/
for(i=0; i<no; i++){
char id[10], name[10], surname[10];
int grade;
printf("\n\nStudent(%d)\n", i+1);
printf("id: ");
scanf("%s", id);
printf("name: ");
scanf("%s", name);
printf("surname: ");
scanf("%s", surname);
printf("grade: ");
scanf("%d", &grade);
studentArray[i] = Student_new(id, name, surname, grade); /*using Student
'constructor' to initialize the array*/
}
for(i=0; i<no; i++){
printf("%s %s %s %d \n", studentArray[i]->id, studentArray[i]-
>name, studentArray[i]->surname, studentArray[i]->grade);
}
return 0;
}
struct Student* Student_new(char* id, char* name, char* surname, int grade)
{
struct Student* st = malloc(sizeof(struct Student));
st->id = id;
st->name = name;
st->surname = surname;
st->grade = grade;
return st;
}
PLEASE HELP!!
The issue is that the loop variables go out of scope after each iteration, and you're left with dangling pointers in the Student instances. What you're seeing is the result of undefined behavior.
What's probably happening is that the same char array is being passed into every student instance. Then you modify the same char array, overwriting the previous values.
You'll need to make copies of the strings. Remember to create a function like Student_free where you free the dynamically allocated copies.
struct Student* Student_new(char* id, char* name, char* surname, int grade)
{
struct Student* st = malloc(sizeof(struct Student));
st->id = strndup(id, 10);
st->name = strndup(name, 10);
st->surname = strndup(surname, 10);
st->grade = grade;
return st;
}
You should reserve memory for the string attributes. As a hint, use a struct similar to:
#define MAX_LEN 32
struct Student{ /*struct for student info*/
char id[MAX_LEN];
char name[MAX_LEN];
char surname[MAX_LEN];
int grade;
};
Define MAX_LEN to something that is reasonable for you, and check that the entered values aren't any longer. Also make sure to strcpy the input values to the struct variables.
The student structure only holds pointers to char arrays.
Now the actual space in memory for the strings is allocated in your for cycle an its lifetime is limited by the scope of the for cycle, accessing it afterwards is undefined behaviour. In your case the space where the strings are has not been reused and overridden yet, so coincidentally you are able to get the last value stored (cases like this can also raise segmentation fault).
You should have a look on some basic tutorial about pointers and c memory model. Allocating the arrays in the struct is a good solution (nucleon's answer). Also the scanf function can overflow you should limit the number of retrieved characters to match the size of allocated array.

Pointer to an array of structures

I'm currently trying to write a program for a student database assignment. After manually setting 3 elements of the structure array, the next 3 students' details are inputted by the user.
I am trying to write a function that finds the oldest age of the 6 students and returns it as a student_t entry at index max. I'm struggling with how to actually give the function the pointer that is pointing to the first element of the array stdt[6] and then using the pointer within the function. I also have no idea how I would go about returning to main the entry that has the highest age. If I'm trying to say that the value of an element of array of structures is equal to some other integer (max), doesn't that mean that max is now some other block of memory with an integer value and not linked to the array? So I'm not sure how I would return the entry that has the highest age after the function determines the max age.
This is all I've written so far:
#include <stdlib.h>
#include <stdio.h>
typedef struct {
char *name;
char *surname;
char *UUN;
char *department;
char gender;
int age;
}student_t;
student_t findOldest(student_t *studentarr, int len){
int i;
int x;
int max;
max=0;
for(i=0;i<len;i++){
(p+i).age=x;
if(x>max){
x=max;
}
}
}
int main() {
int i;
student_t stdt[6]={{"John","Bishop","s1234","Inf",'m',18},{"Lady","Cook","s2345","Eng",'f',21},{"James","Jackson","s33456","Eng",'m',17}};
student_t *p=&stdt[0];
for(i=3;i<6;i++) {
printf("First name: \n");
scanf("%s",stdt[i].name);
printf("Last name: \n");
scanf("%s",stdt[i].surname);
printf("UUN: \n");
scanf("%s",stdt[i].UUN);
printf("Department: \n");
scanf("%s",stdt[i].department);
printf("Gender (m/f): \n");
scanf("%c",stdt[i].gender);
printf("Age: \n");
scanf("%d",stdt[i].age);
}
findOldest(p,6);
return 0;
}
This should work.
student_t findOldest(student_t *p, int len){
int i;
student_t max = *(p+0);
for(i=1;i<len;i++)
{if((*(p+i)).age > max.age)
max = *(p+i);
}
return max;
}
You want to return the student so keep the student in your max variable not the age. And to refer to pointers either use
(p+i)->age > max.age
or use
(*(p+i)).age > max.age
But there are other problems with the code.

What's wrong with using pointer in a struct when passing it to gets()?

I have the following code. In the struct definition, I try to ask user to enter employee's first and last name. But when I run this exe, it exit after the title is entered. Any suggestions?
#include<stdio.h>
#include<string.h>
#define NUMEMPS 10
struct Employee {
char *firstname;
char *lastname;
char *title;
int salary;
};
int main()
{
struct Employee* stuff = malloc(NUMEMPS* sizeof *stuff);
int n,i;
for (n=0; n<NUMEMPS;n++)
{
printf("Please enter number %d Employee's Last name:", n);
fflush(stdout);
gets(stuff[n].lastname);
if (strlen(stuff[n].lastname) == 0)
break;
printf("Please enter number %d Employee's first name:", n);
fflush(stdout);
gets(stuff[n].firstname);
printf("Please enter number %d Employee's title:", n);
fflush(stdout);
gets(stuff[n].title);
printf("Please enter number %d Employee's salary:", n);
fflush(stdout);
scanf("%d", &stuff[n].salary);
getchar();
}
for (i = 0;i<n;i++)
{
printf("{%s,%s,%s,%d}\n",
stuff[i].lastname,
stuff[i].firstname,
stuff[i].title,
stuff[i].salary);
}
return 0;
}
The three char* members of the structure are pointers, so no space is allocated to hold any data.
With the current struct you'd have to do three more allocs for the data:
struct Employee* stuff = malloc(NUMEMPS* sizeof *stuff);
stuff->firstname = malloc(101);
stuff->lastname = malloc(101);
stuff->title = malloc(101);
What you probably want is something like:
struct Employee {
char firstname[101];
char lastname[101];
char title[101];
int salary;
};
Also, though as an aside, you must check your malloc calls for a NULL return.
This code:
struct Employee {
char *firstname;
char *lastname;
char *title;
int salary;
};
...
struct Employee* stuff = malloc(NUMEMPS* sizeof *stuff);
only allocates enough room to store a single struct Employee, that is: three pointers and an integer. There's no storage for the character strings pointed to.
Instead, consider malloc()ing each of the constituent character data and assigning to stuff->firstname (et al), or modify the declaration of struct Employee to include character arrays.

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