Passing a structure to a function [closed] - c

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So I am having a problem when compiling this program, I just can't get it to work, I mean if I put the inputstudent() code inside the main(), it is much easier but I have to place the code in a function, inputstudent() and call in from the main(). I know it sounds very easy but I can't get it.
#include <stdio.h>
#include <stdlib.h>
struct student
{
char surname[50];
int age;
char oname[50];
char address[50];
};
void displaystudent();
void inputstudent();
int main(){
struct student s;
inputstudent(s);
displaystudent(s);
return 0;
}
void inputstudent(struct student s){
printf("Enter the surname: ");
scanf("%s",s.surname);
printf("Enter the other name: ");
scanf("%s",s.oname);
printf("Enter the age: ");
scanf("%d",&s.age);
printf("Enter the address: ");
scanf("%s",s.address);
}
void displaystudent(struct student s)
{
printf("Surname: %s \n",s.surname);
printf("Oname: %s \n",s.oname);
printf("Age: %d \n",s.age);
printf("Address: %s",s.address);
}

Answer 1

In C parameters are passed by value, so any modifications made to a parameter inside the function will be local modifications.
Lets have a look at following code snippet which is basically a very simple version of what you're trying to do:
void GetNumber(int number)
{
printf("Type a number:\n");
scanf("%d", &number); // modifies the local variable `number`?
}
...
int n = 0;
GetNumber(n);
Now what is the value of n right after the call to GetNumber?
Well it's not the number the user has typed, but it's still 0, that is the value n contained prior to the call to GetNumber.
What you need is this:
void GetNumber(int *pnumber)
{
printf("Type a number:\n");
scanf("%d", pnumber); // modifies the value pointed by the pointer pnumber
}
...
int n = 0;
GetNumber(&n); // &n is the memory address of the variable n
You need to read the chapter dealing with pointers in your C textbook.
Other less important problem
Your prototypes
void displaystudent();
void inputstudent();
don't match the corresponding functions.

Answer 2

You are passing your struct by value, that's why the function is not modifying it. You should change your function that is intended to modify the struct to take a struct pointer as argument:
#include <stdio.h>
#include <stdlib.h>
struct student {
char surname[50];
int age;
char oname[50];
char address[50];
};
void displaystudent(struct student s);
void inputstudent(struct student *s);
int main() {
struct student s;
inputstudent(&s);
displaystudent(s);
return 0;
}
void inputstudent(struct student *s) {
printf("Enter the surname: ");
scanf("%s", s->surname);
printf("Enter the other name: ");
scanf("%s", s->oname);
printf("Enter the age: ");
scanf("%d", &s->age);
printf("Enter the address: ");
scanf("%s", s->address);
}
void displaystudent(struct student s) {
printf("Surname: %s \n", s.surname);
printf("Oname: %s \n", s.oname);
printf("Age: %d \n", s.age);
printf("Address: %s", s.address);
}

Answer 3

As mentioned by Michael Walz, use pointers in order to modify structure in function calls. Moreover your function signature and definition does not match that's why compiler is complaining:
#include <stdio.h>
#include <stdlib.h>
struct student {
char surname[50];
int age;
char oname[50];
char address[50];
};
void displaystudent(struct student* pStudent);
void inputstudent(struct student* pStudent);
int main() {
struct student aStudent;
inputstudent(&aStudent);
displaystudent(&aStudent);
return 0;
}
void inputstudent(struct student* pStudent){
printf("Enter the surname: ");
scanf("%s", pStudent->surname);
printf("Enter the other name: ");
scanf("%s", pStudent->oname);
printf("Enter the age: ");
scanf("%d", &pStudent->age);
printf("Enter the address: ");
scanf("%s", pStudent->address);
}
void displaystudent(struct student* pStudent)
{
printf("Surname: %s \n", pStudent->surname);
printf("Oname: %s \n", pStudent->oname);
printf("Age: %d \n", pStudent->age);
printf("Address: %s", pStudent->address);
}

Answer 4

You seem to want the changes that you make to the structure variable s inside inputstudent() to be reflected back to the original variable. In that case you need to pass the address of the variable to the function instead of its value.
If you pass the value of s to the function instead of its address, a new copy of s would be made inside inputstudent() and the values would be read into this copy while the s in main() remains unchanged.
To solve this you give inputstudent() a pointer to the s in main() and make inputstudent() use this address while reading the data. In this way the changes made for the variable in inputstudent() will be reflected back to the s in main().
Call the function like
inputstudent(&s);
And to access members of a structure variable using a pointer to it, you use the -> operator instead of the . operator.
void inputstudent(struct student *s){
printf("Enter the surname: ");
scanf("%s",s->surname);
printf("Enter the other name: ");
scanf("%s",s->oname);
printf("Enter the age: ");
scanf("%d",&s->age);
printf("Enter the address: ");
scanf("%s",s->address);
}
Also, an address possibly involves white spaces in which scanf() won't do. You could use fgets() for that.

Answer 5

There are basically two causes for your problem.
Function declarations don't have any parameters.
The structure is passed by value instead of reference to inputstudent function.
You can solve both of them by changing the function prototypes in both declaration and definition to
void displaystudent(struct student s);
void inputstudent(struct student &s);

Answer 6

You can't use struct student s as parameter in inputstudent(). It is just a value copy.
You should use pointer as parameter.
As:
void inputstudent(struct student* s)
{...}
int main(){
struct student s;
inputstudent(&s);
displaystudent(s);
return 0;
}