My schedule->start.hour points to the currect element of array. How to make it point to the previous element of array?
struct Time {
int hour;
} start, end;
struct Class {
struct Time start, end;
} schedule[100];
I need to use this inside a function which sets start of current to be equal to end of previous.
void add_class(struct Class shedule[]){
schedule->start.hour=schedule*(--).end.hour;
};
It seems you need something like the following
void add_class( struct Class shedule[], size_t n )
{
for ( size_t i = 1; i < n; i++ )
{
shedule[i].start.hour = shedule[i-1].end.hour;
}
//...
}
and the function is called like
add_class( shedule, sizeof( shedule ) / sizeof( *shedule ) );
or like
add_class( shedule, 100 );
Its not really clear what you are after and the code you show is wrong. There are no pointers there at all.
If you want to access different instances of Class in the schedule array you need
schedule[0].start.hour;
schedule[1].start.hour;
....
to loop over them all
for(int i = 0; i < 100; i++){
printf("start=%d, end = %d\n",schedule[i].start.hour, scehdule[i].end.hour);
}
if you have a pointer to a Class instance
void add_class(struct Class shedule[]){
...
};
You can access the prior entry in the array like this
void add_class(struct Class schedule[]){
struct Class *prior = schedule - 1;
schedule->start.hour=prior->end.hour;
};
But , and this is a huge but, this will be very bad if this is the first element in the array.
I would still do it by passing indexes tho.
Related
I have a certain program that lets you register members and save their name and birthdate into arrays. The particular function that does this registration uses the following code;
char regmember (struct member a[])
{
int i = 0;
char wow;
do
{
//registration
printf("\n Do you want to add someone else (y/n):");
scanf(" %c",&wow);
i++
}while(wow != 'n');
int nrofmembers = i;
return nrofmembers;
}
-> I save the user input by using
scanf("%s",a[i].name) and scanf("%d",&a[i].ID);
which is why I am using i++. As you realize, the int variable i, will hold the number of members who have been registered. I want to utilize this info in order to use it in loops in other functions, so I went on to save the value of i in another int variable...
int nrofmembers = i;
My problem is, I can't use that variable (nrofmembers) else where, even though I tried returning it, any advice?
you need both to get i in parameter and to return the new value, you can do
int regmember (struct member a[], int i)
{
... use and modify i
return i;
}
or using it as an input-output variable
void regmember (struct member a[], int * i)
{
... use and modify *i
}
In the first case the caller do for instance :
int i = 0;
for (...) {
...
i = regmember(..., i);
...
}
and in the second case :
int i = 0;
for (...) {
...
regmember(..., &i);
...
}
Suppose you keep the members in a global array, then you can manage how many members are in your array also as a global variable, for example
struct member gMembers[MAX_MEMBERS];
int gnMembers;
Your function can now operate on this array directly:
int regmember (void)
{
if (gnMembers < MAX_MEMBERS)
{
// add member
if (scanf("%s",gMembers[gnMembers].name)==1
&& scanf("%d",&gMembers[gnMembers].ID)==1) {
gnMembers++;
return 1; // success
}
}
return 0; // array full or scanf error
}
I'm new in C programming. I'm developing a priority queue in C'99 with the heap data structure.
I'm using heapifyDown() in combination with swapValues() to sort the heap array for extracting the first element (min-heap) pqueue_extractMin() function. My structure looks like this:
typedef struct ProrityQueue_s PriorityQueue;
typedef struct PriorityQueue_Entry_s *PriorityQueue_Entry;
struct ProrityQueue_s {
int size, last;
char error;
PriorityQueue_Entry *entries;
};
struct PriorityQueue_Entry_s {
char *value;
float priority;
};
For information – Full code for information on gist: https://gist.github.com/it4need/ddf9014bfda9fe6a64bb01a7417422bc
Questions:
Insertion into the Priority queue ("minheap") looks good. Everything is fine. But when I'm extract more than one element at once, I will get this error: "Process finished with exit code 11".
Is this line allowed to copy the whole contents of the last element to the first of the heap? priorityqueue->entries[0] = priorityqueue->entries[priorityqueue->last];
swapValues(priorityqueue, currentPositionIndex, smallestChild); Can I swap values of whole Structure elements? -> implementation (bottom).
HeapifyDown():
void heapifyDown(PriorityQueue *priorityqueue)
{
int currentPositionIndex = 0;
while(currentPositionIndex < priorityqueue->last)
{
int smallestChild = currentPositionIndex;
int leftChildIndex = (2 * currentPositionIndex) + 1;
int rightChildIndex = (2 * currentPositionIndex) + 2;
smallestChild = (priorityqueue->entries[leftChildIndex]->priority < priorityqueue->entries[smallestChild]->priority && priorityqueue->last > leftChildIndex)
? leftChildIndex : smallestChild;
smallestChild = (priorityqueue->entries[rightChildIndex]->priority < priorityqueue->entries[smallestChild]->priority && priorityqueue->last > rightChildIndex)
? rightChildIndex : smallestChild;
if(smallestChild == currentPositionIndex)
{
break;
}
swapValues(priorityqueue, currentPositionIndex, smallestChild); // #todo: Why does this line break the function on two function calls by negative values
currentPositionIndex = smallestChild;
}
}
SwapValues():
void swapValues(PriorityQueue *priorityqueue, int firstIndex, int secondIndex)
{
// #todo: Does this work properly?
PriorityQueue_Entry tmp_entry = priorityqueue->entries[firstIndex];
priorityqueue->entries[firstIndex] = priorityqueue->entries[secondIndex];
priorityqueue->entries[secondIndex] = tmp_entry;
}
extractMin():
char *pqueue_extractMin(PriorityQueue *priorityqueue)
{
if(isEmpty(priorityqueue))
{
priorityqueue->error = ERROR_PRIORITY_QUEUE_EMPTY;
}
priorityqueue->last--;
char *tmp = priorityqueue->entries[0]->value;
priorityqueue->entries[0] = priorityqueue->entries[priorityqueue->last]; // #todo: Is this allowed?
heapifyDown(priorityqueue); // #todo: Why does this line break the extractMin() function on two function calls -> check swapValues() in heapifyDown()
return tmp;
}
Full code for information on gist: https://gist.github.com/it4need/ddf9014bfda9fe6a64bb01a7417422bc
I have an struct which defines an array of structs, each of which contain a couple more arrays. These inner arrays define my 'datasets'.
In numerous places, I wish to iterate over all the datasets. To avoid 3 nested loops, I loop over the total number of datasets and have a few if statements to keep track of which array I need to access. It looks like this:
int datasetCount = 0;
int defendedDatasetCount = 0;
int i;
Dataset *ds;
for (i = 0 ; i < totalDatasets ; i++)
{
// If we have passed the number of datasets in this group, move to the next group
if (datasetCount == (dg->nDatasets + dg->nDefDatasets))
{
dg++;
datasetCount = 0;
defendedDatasetCount = 0;
}
// If we have gone through all the (undefended) datasets, read from thte defended datasets
if (datasetCount >= dg->nDatasets)
{
ds = &(dg->defDatasets[defendedDatasetCount]);
defendedDatasetCount++;
}
else
{
ds = &(dg->datasets[datasetCount]);
}
where dg is the pointer to a struct which is simply an array of structs and a size counter.
I find myself repeating this boilerplate code for iterating through the datasets in a few functions which do different things.
I'm struggling to be able to come up with something like this:
while (give_me_next_dataset(dg) == TRUE)
{
...
}
is it possible?
It's possible, but the proposed API isn't very nice. You're going to have to put iteration state somewhere, and you're not leaving any room for that.
I would propose something like:
struct DgIter {
struct Dg *dg;
size_t index;
size_t dataSet;
};
Then you can have functions like:
struct DgIter iter_start(struct Dg *dg)
{
const struct DgIter iter = { dg, 0, 0 };
return iter;
}
void * iter_next_dataset(struct DgIter *iter)
{
// check if there is a current dataset, else return NULL
// update fields in iter as necessary
}
I have tried to create a CD struct like :
typedef struct
{
char* nameCD;
int yearOfpublication;
song* listOfSongs;
int priceCD;
int numberOfSongs;
} CD;
and I have a song struct :
typedef struct
{
char* nameSong;
char* nameSinger;
int lenghtOfSong;
} song;
void SongInput(song *psong, CD *pcd)
{
pcd->numberOfSongs++;
pcd->listOfSongs = (song*)malloc(pmcd->numberOfSongs*sizeof(song));
// here all the code that update one song..
but what should I write to update the next song?
how do I change it into an array which update the number of the songs and how can I save all the songs?
I tried this :
printf("Enter lenght Of Song:");
scanf("%d", &psong->lenghtOfSong);
but I don't understand the pointers..
and how to update the next song?
}
void CDInput(CD *pcd)
{
int numberOfSongs = 0;
//here all the other update of cd.
//songs!!!!!!!!!!!!!!!!!!!!!!!!!!!!
pcd->numberOfSongs = 0;
pcd->listOfSongs = (song*)malloc(numberOfSongs*sizeof(song));
}
Do I need to write anything else?
void CDInput(CD *pcd)
{
int i;
//...
printf("Enter number Of Song:");
scanf("%d", &pcd->numberOfSongs);
pcd->listOfSongs = (song*)malloc(pcd->numberOfSongs*sizeof(song));
for(i = 0; i < pcd->numberOfSongs; ++i){
SongInput(&pcd->listOfSongs[i]);
}
//...
}
It depends on if you want to write the structure once completely or you really want to add one item.
For the first case, please refer to BLUEPIXY's answer, for the second one, thigs are slightly more complicated.
bool add_song(song *psong, CD *pcd)
{
song* newone = realloc(pcd->listOfSongs, (pmcd->numberOfSongs+1)*sizeof(song));
if (!newone) {
// return and complain; the old remains intact.
return false; // indicating failure.
}
// now we can assign back.
pcd->listOfSongs = newone;
newone[pcd->numberOfSongs++] = *psong;
return true; // indicating success.
}
I have my code below that consits of a structure, a main, and a function. The function is supposed to display two parameters that have certain values, both of which point to the same structure.
The problem I dont know how to add the SECOND parameter onto the following code :
#include<stdio.h>
#define first 500
#define sec 500
struct trial{
int f;
int r;
float what[first][sec];
};
int trialtest(trial *test);
main(){
trial test;
trialtest(&test);
}
int trialtest(trial *test){
int z,x,i;
for(i=0;i<5;i++){
printf("%f,(*test).what[z][x]);
}
return 0;
}
I need to add a new parameter test_2 there (IN THE SAME FUNCTION) using this code :
for(i=0;i<5;i++){
printf("%f,(*test_2).what[z][x]);
How does int trialtest(trial *test) changes ?
and how does it change in main ?
I know that I should declare test_2 as well, like this :
trial test,test_2;
But what about passing the address in the function ? I do not need to edit it right ?
trialtest(&test); --- This will remain the same ?
So please, tell me how would I use test_2 as a parameter pointing to the same structure as test, both in the same function..
Thank you !!
Please tell me if you need more clarification
I think that this is your homework, so I'll just write a different function that may give you an idea of what (I think) you need to do. I read that you don't want to change the trail_test parameter list, so I stuck with a similar parameter list.
struct thing {
/* put some stuff here */
};
typedef struct thing thing; /* because this is C, not C++ */
int how_many_things(thing * thing_list);
int main(void) {
int i;
thing * a;
int count_init = random(); /* let's surprise ourselves and make a random number of these */
count_init %= 128; /* but not too many or it might not work at all */
a = malloc(count_init*sizeof(things)+1);
for (i = 0; i < count_init; i++) {
thing_init(&(a[i]));
}
make_illegal_thing(&(a[count_init]) ); /* like '\0' at the end of a string */
printf("There are %i things in the list\n", how_many_things(a) );
return 0;
}
/* This is very similar to strlen */
int how_many_things(thing * a) {
int count = 0;
while (is_legal_thing(a) ) {
a++;
count++;
}
return count;
}