I know I for sure misunderstand how to use pointers again. So here is my code. Would be nice if you all can help me. The program is simple. You write values in a structure array and print them out. Even so it would be nice if someone could explain to me when to use double pointers and how to use them probably.
#include <stdio.h>
#include <stdlib.h>
#define MAXA 3
typedef enum{
FOOD,
ART,
OTHERS
}TKindOfArticle;
typedef struct{
int number;
char description[31+1];
int sellingGrossPrice;
int vat;
int minimumStockLevel;
TKindOfArticle kindOf;
}TArticle;
void readOneArticle(TArticle* arti);
int readMaxArticle(TArticle* arti[]);
void printfOneArticle(TArticle arti);
void printfMaxArticle(TArticle *arti[],int read);
int main()
{
TArticle arti[MAXA];
int howMany;
howMany = readMaxArticle(&arti);
printfMaxArticle(&arti,howMany);
return 0;
}
void readOneArticle(TArticle* arti){
printf("Number: ");
scanf("%d", &(arti->number));
printf("Descrip: ");
scanf("%s", &(arti->description));
printf("SellGrossPrice: ");
scanf("%d",&(arti->sellingGrossPrice));
printf("MinimumStock: ");
scanf("%d",&(arti->minimumStockLevel));
printf("Kind of article (0: Food, 1: Art, 2: Others): ");
scanf("%d",&(arti->kindOf));
if(arti->kindOf == FOOD){
arti->vat= arti->sellingGrossPrice*1.1;
} else if(arti->kindOf == ART){
arti->vat= arti->sellingGrossPrice*1.13;
}else if(arti->kindOf == OTHERS){
arti->vat= arti->sellingGrossPrice*1.2;
}
}
int readMaxArticle(TArticle* arti[]){
int read;
int i=0;
printf("Max Elements (max. 3): ");
scanf("%d",&read);
if(read>MAXA){
printf("Error");
} else{
for(i=0; i<read;i++){
readOneArticle(arti[i]);
printf("\n");
printf("Number: %d\nDescrip.: %s\nSell Gross: %d\nVat: %d\nMin. Stock: %d\n",
(*arti[i]).number,(*arti[i]).description,
(*arti[i]).sellingGrossPrice,(*arti[i]).vat,(*arti[i]).minimumStockLevel);
}
}
return read;
}
void printfOneArticle(TArticle arti){
printf("Number: %d\nDescrip.: %s\nSell Gross: %d\nVat: %d\nMin. Stock: %d\n",
arti.number,arti.description,
arti.sellingGrossPrice,arti.vat,arti.minimumStockLevel);
switch(arti.kindOf){
case 0: printf("Kind: Food\n");
break;
case 1: printf("Kind: Art\n");
break;
case 2: printf("Kind: Others\n");
break;
}
}
void printfMaxArticle(TArticle *arti[],int read){
if(read>MAXA){
} else{
for(int i=0; i<read;i++){
printfOneArticle(*arti[i]);
printf("\n");
}
}
}
You are creating an array of structures: TArticle arti[MAXA];
But when you call readMaxArticle(&arti) function you pass pointer to array of TArticle. TArticle *arti[] it reads like this - arti is array of pointers to TArticle. But you want to pass pointer to array of TArticle. It won't compile anyway.
error: cannot convert 'TArticle (*)[3]' to 'TArticle**'
You might want to look at how to read C declaration and if you want to practice visit this site.
Related
I'm doing self-study on C Programming, and I have been recommended the following C Program by my colleagues to study further, where you can enter the Name and Age and it displays and uses Insert, Delete, Display, and Exit menu options.
I'm trying to convert it to my current study stream logic scenario where I need to enter the Name, Exercise Mark 1 (up to 3), and then it computes the Average and gets displayed while employing the Insert, Delete, Display, Update (updating the scores only, not the names), Delete and Exit.
Any guidance please on how to learn this code and understand the logic, and apply it to the 2nd scenario will be much appreciated.
Here is the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 50
//using parallel arrays as fields in the list
typedef struct list{
char name[MAX][31];
int age[MAX];
int last;
}LIST;
LIST L;//L structure is global
void save();
void retrieve();
void makenull();
void insert(char n[31],int a);
void del(char n[31]);
void display();
int locate(char n[31]);
int isfull();
int isempty();
int menu();
int main(){
char nm[31];
int ag;
makenull();
retrieve();
while(1){
switch(menu()){
case 1: system("cls");printf("Insert Mode\n");
printf("Input Name: ");scanf("%s",nm);
printf("Input Age: ");scanf("%d",&ag);insert(nm,ag);break;
case 2: system("cls");printf("Delete Mode\n");
printf("Input Name: ");scanf("%s",nm);del(nm);break;
case 3: display();break;
case 4: save();exit(0);
default: printf("\n1-4 lang!\n");system("pause");
}
}
return 0;
}
void makenull(){
L.last = -1;
}
void insert(char n[31],int a){
if (isfull()){
printf("List is full.\n");
system("pause");
}
else {
L.last++;
strcpy(L.name[L.last],n);
L.age[L.last]=a;
}
}
void del(char n[31]){
int p;
if (isempty()){
printf("List is empty.\n");
system("pause");
}
else {
p=locate(n);
if (p==-1){
printf("Not found.\n");
system("pause");
}
else{
for(int i = p;i<L.last;i++){
strcpy(L.name[i],L.name[i+1]);
L.age[i]=L.age[i+1];
}
L.last--;
printf("Successful delete operation.\n");
system("pause");
}
}
}
void display(){
int i;
system("cls");
printf(" Name Age \n");
for(i=0;i<=L.last;i++)
printf("%d.) %s %d\n",i+1,L.name[i],L.age[i]);
system("pause");
}
int locate(char n[31]){
int i;
for (i=0;i<=L.last;i++)
if(strcmp(L.name[i],n)==0)
return i;
return -1;
}
int isfull(){
if (L.last==MAX-1)
return 1;
else
return 0;
}
int isempty(){
return(L.last==-1);
}
int menu(){
int op;
system("cls");
printf("MENU\n");
printf("1. Insert\n");
printf("2. Delete\n");
printf("3. Display\n");
printf("4. Exit\n");
printf("\nSelect(1-4): ");
scanf("%d",&op);
return(op);
}
void save(){
FILE *fp;
int i;
fp=fopen("Practice4.dbf","w+");
if (fp==NULL){
printf("File Error.\n");
system("pause");
}
else{
for (i=0;i<=L.last;i++)
fprintf(fp,"%s %d\n",L.name[i],L.age[i]);
}
fclose(fp);
}
void retrieve(){
FILE *fp;
char n[31];
int i,a;
fp=fopen("Practice4.dbf","r+");
if (fp==NULL){
printf("File Error.\n");
system("pause");
}
else {
while(!feof(fp)){
fscanf(fp,"%s %d\n",n,&a);
insert(n,a);
}
}
fclose(fp);
}
Your code isn't properly formatted and there are no comments. I can't give you a direct answer with some code in it, but summing up all my comments (and of course I deleted them), this is what I've to say:
Consider this scenario-
if your .dbf has more than MAX 50 elements, then your while (!feof(fp)) inside retrieve() will keep calling insert() and insert() will keep executing its if () { } block.
You should put something like while (!feof(fp) && L.last < MAX) to prevent that situation and you'll need to further modify your code in insert(). Another thing is, this code doesn't have any update() function and scores variable. You'll need to add scores in your struct as well as there must be scores fields in your .dbf.
Now, for a moment let's say everything else is good to go in your code, then you should follow these following steps:
Declare variables
char nameInput[31];
float ex_marks[3], sum = 0, avr = 0;
in main().
Add another case 5 in your switch () block inside main() and translate and convert the following pseudocode into C code:
Read name in nameInput
locate()
if found then
3.a for i = 0 to 2
Read marks in ex_marks[i]
sum = sum + ex_marks[i]
3.b Calculate avr = sum / 3
3.c Display name and avr
else
Display name is not in the list.
exit
Also read about why is while(!feof()) always wrong?
I have a function with a book struct array, but when i try to return it to my main it does not return the values and store them in the array. If the addBook function has to be void how would i work around that so that i can access the array elements later.
void addBook(struct Book book[], int *size) {
if (*size == MAX_BOOKS) {
printf("The inventory is full\n");
}
else {
printf("ISBN:");
scanf("%d", &book[*size]._isbn);
printf("Title:");
scanf("%s", book[*size]._title);
getchar();
printf("Year:");
scanf("%d", &book[*size]._year);
printf("Price:");
scanf("%f", &book[*size]._price);
printf("Quantity:");
scanf("%d", &book[*size]._qty);
*size++;
printf("The book is successfully added to the inventory.\n");
}
return book;
}
int main(void) {
struct Book book[MAX_BOOKS];
int size = 0;
int i;
int option;
printf("Welcome to the Book Store\n");
printf("=========================\n");
do {
menu();
printf("Select: ");
scanf("%d", &option);
switch (option) {
case 0:
printf("Goodbye!\n");
break;
case 1:
displayInventory(book, size);
break;
case 2:
addBook(book, &size);
break;
case 3:
//checkPrice();
break;
default:
printf("Invalid input, try again:\n");
}
} while (option != 0);
}
Your return statement isn't going to do what you're intending as the addBook's function signature says it returns void. I'm surprised that the code as is actually compiled without an error about this.
Anyways, the book data can be returned from the same way it was passed in - as an input and output parameter.
Essentially your code could look like the following (which is only meant to be an example of code that compiles and works to save info entered in from standard input into the book):
#include <stdio.h>
struct Book {
int value;
};
#define MAX_BOOKS 2
void addBook(struct Book book[], int *size) {
if (*size == MAX_BOOKS) {
printf("The inventory is full\n");
}
else {
printf("Value:");
scanf("%d", &book[*size].value);
(*size)++;
printf("The book is successfully added to the inventory.\n");
}
}
int main(void) {
struct Book book[MAX_BOOKS];
int size = 0;
addBook(book, &size);
printf("Book 1: Value=%d\n", book[0].value);
}
And here's how this looks when run:
$ ./main
Value:9
The book is successfully added to the inventory.
Book 1: Value=9
Hope this answers your question.
I think your problem is in the line *size++;. You should use parenthesis, otherwise you are modifying the pointer to size, not the value. It should be (*size)++.
Also, the addBook function should not return anything, since it is void, and it is changing the content of the array book already.
I've got this code, but it doesnt work, what's wrong?
I try to make massive of struct with dynamic size(C language)
after the second use of add_sala(); in main function Windows close programm.
Please help to solve this problem! Thanks!
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <malloc.h>
char trash[50];
int dyn_sala_id=1;
typedef struct
{
int id;
char number[6];
int persons;
char tech_inf[256];
} sala;
sala *sala_;
int add_sala()
{
int persons;
char number[6], tech_inf[256];
sala_ = (sala*)realloc(sala_,dyn_sala_id * sizeof(sala));
printf("Wpisz numer sali(max. 5 znakow): ");
fgets(number,6,stdin);
if(strlen(number)>5)
{
printf("Numer musi byc nie wiecej, niz 5 znakow!\n");
fflush(stdin);
add_sala();
return 0;
}
printf("Wpisz ilosc osob, ktora wmiesci sie w sale(max. 1000 osob): ");
scanf("%d", &persons);
if(persons==0 || persons>1000)
{
printf("Nie wolno wprowadzic litery oraz max. ilosc osob to 1000\n");
fflush(stdin);
add_sala();
return 0;
}
printf("Wpisz info o wyposazeniu sali(max. 255 znakow): ");
fgets(trash,50,stdin);
fgets(tech_inf,256,stdin);
if(strlen(tech_inf)>255)
{
printf("Info musi byc nie wiecej, niz 255 znakow!\n");
fflush(stdin);
add_sala();
return 0;
}
sala_[dyn_sala_id].id = dyn_sala_id;
strncpy(sala_[dyn_sala_id].number, number, 6);
sala_[dyn_sala_id].persons = persons;
strncpy(sala_[dyn_sala_id].tech_inf, tech_inf, 256);
printf("\nSala zostala dodana!\n\n");
printf("%d, %d, %s, %s",dyn_sala_id, persons, number, tech_inf);
dyn_sala_id+=1;
return 0;
}
int main()
{
add_sala();
printf("%s",sala_[1].number);
add_sala();
printf("'%s'",sala_[1].number);
printf("'%s'",sala_[2].number);
return 0;
}
Arrays in C are indexed from 0, so in main() the array indexing is off by 1.
add_sala();
printf("%s",sala_[1].number);
add_sala();
printf("'%s'",sala_[1].number);
printf("'%s'",sala_[2].number);
Also in the function add_sala() it is clear that the first time it is called you have the global
int dyn_sala_id=1;
which you use to allocate memory for one record with
sala_ = (sala*)realloc(sala_,dyn_sala_id * sizeof(sala));
but a bit further down, the indexing is again off by 1, where there is plainly only one array element
sala_[dyn_sala_id].id = dyn_sala_id;
Then, in that same function (although I can't read the error messages) it seems strange that after an apparent bad input, you recurse the function. Also, you have undefined behaviour with
fflush(stdin);
and I have not looked further, because the code will not work.
I am new to C and very much interested in knowing how to approach any problem which has more than 3 or 4 functions, I always look at the output required and manipulate my code calling functions inside other functions and getting the required output.
Below is my logic for finding a students record through his Id first & then Username.
This code according to my professor has an excessive logic and is lacking in many ways, if someone could assist me in how should I approach any problem in C or in any other language it would be of great help for me as a beginner and yes I do write pseudo code first.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct{
int id; //Assuming student id to be unique
int age;
char *userName; //Assuming student userName to be unique
char *dept;
}student; // Alias "student" created for struct
student* createstruct(); // All function prototype declared
student* createArray();
void addstruct(student* s2);
void searchChar(student* s2,int num);
void searchInt(student* s2,int num);
student* createstruct() // function createStruct() to malloc data of struct student.
{
student *s;
s = (student*)malloc(sizeof(student));
s->userName = (char*)malloc(sizeof(char)*32);
s->dept = (char*)malloc(sizeof(char)*32);
printf("please enter id ");
scanf("%d",&s->id);
printf("please enter age ");
scanf("%d",&s->age);
printf("please enter userName ");
scanf("%31s",s->userName);
printf("please enter department ");
scanf("%31s",s->dept);
printf("\n");
return s;
}
student* createArray()
{
student *arr; //declaration of arr poiter, type struct student
arr = (student*)malloc(sizeof(student)*10); // memory allocated for a size of 10
return arr;
}
void addstruct(student *s2) // function for adding data to the structures in array
{
int i,num;
student* s1;
printf("please enter the number of records to add:");
scanf("%d",&num);
printf("\n");
if(num>0 && num<11)
{
for(i=0;i<num;i++) // if user want to enter 5 records loop will only run 5 times
{
s1 = createstruct();
s2[i].id = s1->id; // traversing each element of array and filling in struct data
s2[i].age = s1->age;
s2[i].userName = s1->userName;
s2[i].dept= s1->dept;
}
}
else if(num>10) // if user enters more than 10
{
for(i=0;i<10;i++) // loop will still run only 10 times
{
s1 = createstruct();
s2[i].id = s1->id;
s2[i].age = s1->age;
s2[i].userName = s1->userName;
s2[i].dept = s1->dept;
}
printf("Array is full"); // Array is full after taking 10 records
printf("\n");
}
searchInt(s2,num); // Calling searchInt() function to search for an integer in records
searchChar(s2,num); // Calling searchChar() function to search for a string in records
free(s1);
free(s2);
}
void searchChar(student* s2,int num) // function for searching a string in records of structure
{
char *c;
int i;
c = (char*)malloc(sizeof(char)*32);
printf("please enter userName to search ");
scanf("%31s",c);
printf("\n");
for (i=0;i<num;i++) //num is the number of struct records entered by user
{
if ((strcmp(s2[i].userName,c)==0)) //using strcmp for comparing strings
{
printf("struct variables are %d, %d, %s, %s\n", s2[i].id,s2[i].age,s2[i].userName,s2[i].dept);
break;
}
else if(i == num-1)
{
printf("nothing in userName matches: <%s>\n",c);
break;
}
}
}
void searchInt(student* s2,int num) //searchs for an integer and prints the entire structure
{
int i,z;
printf("please enter id to search ");
scanf("%d",&z);
printf("\n");
for (i=0;i<num;i++)
{
if (s2[i].id == z)
{
printf("struct variables are %d, %d, %s, %s\n\n", s2[i].id,s2[i].age,s2[i].userName,s2[i].dept);
break;
}
else if(i == num-1)
{
printf("nothing in id matches: <%d>\n\n",z);
break;
}
}
}
int main(void)
{
student *s2;
s2 = createArray();
addstruct(s2);
return 0;
}
I'm not going to go into optimizing, because if you wanted better theoretical performance you would probably go with different data structures, such as ordered arrays/lists, trees, hash tables or some kind of indexing... None of that is relevant in this case, because you have a simple program dealing with a small amount of data.
But I am going to tell you about the "excessive logic" your professor mentioned, taking your searchInt function as an example:
for (i=0;i<num;i++)
{
if (s2[i].id == z)
{
printf("struct variables are %d, %d, %s, %s\n\n", s2[i].id,s2[i].age,s2[i].userName,s2[i].dept);
break;
}
else if(i == num-1)
{
printf("nothing in id matches: <%d>\n\n",z);
break;
}
}
The thing here is that every time around the loop you're testing to see if you're at the last element in the loop. But the loop already does that. So you're doing it twice, and to make it worse, you're doing a subtraction (which may or may not be optimized into a register by the compiler).
What you would normally do is something like this:
int i;
student *s = NULL;
for( i = 0; i < num; i++ )
{
if( s2[i].id == z ) {
s = &s2[i];
break;
}
}
if( s != NULL ) {
printf( "struct variables are %d, %d, %s, %s\n\n",
s->id, s->age, s->userName, s->dept );
} else {
printf("nothing in id matches: <%d>\n\n",z);
}
See that you only need to have some way of knowing that the loop found something. You wait for the loop to finish before you test whether it found something.
In this case I used a pointer to indicate success, because I could then use the pointer to access the relevant record without having to index back into the array and clutter the code. You won't always use pointers.
Sometimes you set a flag, sometimes you store the array index, sometimes you just return from the function (and if the loop falls through you know it didn't find anything).
Programming is about making sensible choices for the problem you are solving. Only optimize when you need to, don't over-complicate a problem, and always try to write code that is easy to read/understand.
My function code for peek is not working? why is that? can anyone help me with my peek function?
#include<stdio.h>
#include<stdlib.h>
#define maxsize 10
int stack[maxsize];
int stacktop=0;
void instructions();
int process();
int push(int value);
int pop();
void display();
void peek();
int main()
{
process();
getch();
}
int process()
{
int val;
int choice;
do
{
instructions();
printf("Enter Your Choice: ");
scanf("%d",&choice);
switch( choice )
{
case 1:
printf("\nElement to be Pushed : ");
scanf("%d",&val);
push(val);
break;
case 2:
val=pop();
if(val!=-1)
{
printf("Popped Element : %d\n",val);
}
break;
case 3:
peek();
break;
case 4:
display();
break;
case 5:
break;
}
}while(choice !=5);
}
void instructions()
{
printf("Enter Your choice for the following process\n");
printf("\n[1]Push a Node on top of the list");
printf("\n[2]Pop a node off the list");
printf("\n[3]Peek The Top Node");
printf("\n[4]Display The Whole list");
printf("\n[5]Exit The Program\n");
}
int push(int val)
{
if(stacktop<maxsize)
{
stack[stacktop++]=val;
}
else
{
printf("Stack is full");
}
}
int pop()
{
int a;
if(stacktop>0)
{
a=stack[--stacktop];
return a;
}
}
void display()
{
int i;
i = 0;
if(stacktop>0)
{
printf("Elements are:");
while(i<stacktop)
{
printf("\n%d--\n",stack[i++]);
}
}
}
void peek()
{
printf("%d",stacktop);
}
Is it supposed to be:
printf("%d\n", stack[stacktop - 1]);
Print the contents, rather than the size of the stack?
Obviously you'd also need to bounds check to make sure you're not printing outside of the range of your stack (when it's empty)
I know this isn't Code Review, but I thought I would give you a few bits of advice.
When you call scanf, always check the result. For example, if the user enters something other than a decimal number, your code will end up putting an indeterminate value into the choice or val variables. The scanf function returns the number of items that were successfully read. If you asked for one item, and scanf returns 1, then you can rely on the value of that object:
int choice;
if (scanf("%d", &choice) != 1)
// handle error, can't rely on value of "choice"
else
// continue onwards, can rely on value of "choice"
Usually, the \n escapes go at the end of the string literal, not at the beginning. It is more common to do it this way, but it doesn't mean it should always go at the end.
printf("Enter Your choice for the following process\n\n");
printf("[1]Push a Node on top of the list\n");
printf("[2]Pop a node off the list\n");
printf("[3]Peek The Top Node\n");
For outputting simple strings, consider just using the puts function, which automatically appends the new-line character for you:
puts("Enter Your choice for the following process");
puts("");
puts("[1]Push a Node on top of the list");
puts("[2]Pop a node off the list");
puts("[3]Peek The Top Node");
Your display method is a perfect example of when to use a for loop instead of a while loop. Generally speaking, use a for loop when you know exactly how many items you have and you want to iterate over each of them:
void display()
{
int i;
puts("Elements are:");
for (i = 0; i < stacktop; i++)
printf("\n%d--\n", stack[i]);
}
To reverse the order of the stack, simply start at the top and go backwards:
void display()
{
int i;
puts("Elements are:");
for (i = stacktop - 1; i >= 0; i--)
printf("\n%d--\n", stack[i]);
}