c 使用结构体的数据库程序

Question

I'm make a program in c that display a database using structures, I'm kinda new to programming also I know c++ and i make the program also for c++ but I have a problem in both programs. I will post only the c code. So the program works fine until I saw that is not printed the values I entered, it prints random values(it's garbage memory I guess). I don't know why this is working have a look:

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
typedef struct database{
char dataname[32],date[32];
int  number_employers;
float  profit;
double salary;
}database;
void new_company(database x);
void show_company(database x);

int main()
{
database Tarom,Wizzair;
new_company(Tarom);
system("cls");
new_company(Wizzair);
system("cls");
show_company(Tarom);
show_company(Wizzair);
return 0;
}

void new_company(database x){
printf("Enter company name: ");
scanf("%s",&x.dataname);
printf("\nEnter company date: ");
scanf("%s",&x.date);
printf("\nEnter number of employers:");
scanf("%d",&x.number_employers);
printf("\nEnter the average salary of employers:");
scanf("%f",&x.salary);
printf("\nEnter the company profit(in proccent):");
scanf("%f",&x.profit);
}

void show_company(database y){
printf("Company name:%s\n",y.dataname);
printf("Company date:%s\n",y.date);
printf("Number of employers:%d\n",y.number_employers);
printf("Average salary of employers:%f\n",y.salary);
printf("Company profit:%f\n***************************\n",y.profit);
}

Answer 1

void new_company(database x){

You passed the object by value, so the function gets a local copy. Any changes to the object made inside the function affect only the local copy, not the original. That is your problem.

In C++, the correction to that problem is simpler. You just change the signature of the function to

void new_company(database& x){

In C, the change is more difficult. You need & in front of the object name where the caller passes it to the function, and you need * in front of the name in the function signature, and you need to change all the . used to access members of the object inside the function to ->

Answer 2

Because you're passing the database object by value, so a copy of the (uninitialized) dictionary objects is being passed in, and it's this copy that's being updated by new company. Pass in the address of the dictionaries, eg

new_company(&Tarom);

and change new_company definition to take a pointer to a database, like:

void new_company(database* x){