so I'm really new at this, and I was wondering how I would go about passing a local variable in a function (in terms of the initialization). For example, I have one function (move) that declares and initializes two variables (t_row and t_column) to be used in a for loop, and within that loop, I have another functions (swap), that is called if certain conditions are met. How do I go about using those variables in the swap function. I know I need to declare them, but their initialization in the swap function depends on what iteration of the for loop swap was called. Thanks in advance for any help!
bool move(int tile)
{
for (int t_row = 0; t_row < d; t_row++)
{
for (int t_column = 0; t_column < d; t_column++)
{
if (tile == board[t_row][t_column])
{
if (0 < t_row && board[t_row - 1][t_column] == 0)
{
swap(t_row - 1, t_column);
return true;
}
}
}
}
return false;
}
void swap(int row_new, int column_new)
{
int t_row;
int t_column;
int hold = board[t_row][t_column];
board[t_row][t_column] = 0;
board[row_new][column_new] = hold;
}
The easiest way I can see to do this would be to pass in the values of the old row and column.
void swap(int row_new, int col_new, int row_old, int col_old) {
int hold = board[row_old][col_old];
board[row_old][column_old] = 0;
board[row_new][column_new] = hold;
}
Related
my work:
#define SIZE 9
#include <stdbool.h>
bool arrayCheck(int arr[], int counter, int array_size);
void main() {
int arr[SIZE] = { 1,2,5,1,5,1,2,3,4},num1=5;
bool check= arrayCheck(arr, num1, SIZE - 1);
}
bool arrayCheck(int const arr[], int counter, int array_size) {
if (counter == 0) {
return true;
}
if (array_size < 0) {
return false;
}
if (arr[array_size] - arr[array_size - 1] == 1) {
counter -= 1;
array_size -= 1;
}
else {
counter = 5;
array_size -= 1;
}
arrayCheck(arr, counter, array_size);
}
im writing a recursion function that should read an array and if there is a requested number of follow up numbers (defined by counter) the function will return "true" other wise the function will return "falls"
in my code the function works only if the the request amount of follow up numbers is 5 (cuz that was the number i was testing the function with) now im thinking if i can create and initiate a variable that wont re-initiate itself each time that would be the way. is it possible?
To initialize a variable once and only once within the scope of a function, use the static keyword when declaring the variable.
For example, the counter variable below will only set to its initial value (0) once if defined within a function. Each subsequent call to foo will result in counter incrementing by 1. The first call will make counter = 1, 2nd call will make counter = 2, etc.
void foo( void )
{
static int counter = 0;
counter++;
}
I am trying to create a function that will take in the positions of numerous bodies moving in circular motion, and output their orbital periods. Each body is stored in a struct which contains its X, Y and Z co-ordinate (as well as some other information I don't need for this specific task).
My current function for doing this is:
double calc_period(Body *bodies, double t, int Nbodies, int i)
{
double orbit_angle[Nbodies];
double initial_angle[Nbodies];
double last_angle[Nbodies]
double last_time[Nbodies];
double half_step[Nbodies];
double running_total[Nbodies];
double orbitN[Nbodies];
double average_period[Nbodies];
orbit_angle[i] = atan(bodies[i].r[Y] / bodies[i].r[X]);
if (t==0) {
//Initialise all the variables to 0 the first time through
last_angle[i] = 0;
initial_angle[i] = orbit_angle[i];
orbitN[i] = 0;
half_step[i] = 1;
}
if (last_angle[i] < initial_angle[i] && orbit_angle[i] > initial_angle[i]) {
if (half_step[i] == 0) {
if (orbitN[i]==0) {
last_t[i] = t;
running_total[i] = t;
} else {
running_total[i] += t - last_t[i];
last_t[i] = t;
}
orbitN[i]++;
average_period[i] = running_total[i] / (DAYS_TO_SECS * orbitN[i]);
half_step[i] = 1;
} else if (half_step[i] == 1) {
half_step[i] = 0;
}
}
last_angle[i] = orbit_angle[i];
return average_period[i];
}
and this function is called in main like so:
for (double j = 0; j < max_time; j += timestep) {
update_positions(bodies, Nbodies, j);
for (int i = 0; i < Nbodies; i++) {
average_period[i] = calc_period(bodies, j, Nbodies, i);
if (j > max_time - timestep) {
printf("%s average period: %lg\n", bodies[i].name, average_period[i]);
}
}
}
and the problem that I'm having is that of course when the calc_period function finishes, the variables within are destroyed, so it cannot remember what initial_angle, last_angle or last_t were, so doesn't work. However I'm struggling to come up with a solution for this. If anyone can give any guidance it would be much appreciated.
Any data in the stack is volatile within function calls. The space in the stack you are using now will be replaced on future function calls, so functions on the stack should be used just until the function ends.
For your problem different methods exists.
You can create a struct as a global variable which will be stored in BSS, you can create a global pointer pointing to your struct on dynamic memory, allocated with functions like malloc().
Also you can create a static variable so on future calls to that function you can use it.
The best solution would be either defining a static pointer to malloc() where your struct resides, or doing the same on a global variable as a pointer.
Below, I've defined a Map struct in C. It functions as a map, with setValue and getValue functions. Key values default to -1.
typedef struct {
int key;
int value;
} Index;
typedef Index Map[1000];
void initMap(Map *map)
{
for (int i = 0; i < 1000; i++)
{
Index thisIndex = *map[i];
thisIndex.key = -1;
thisIndex.value = 0;
}
}
int getValue(Map *map, int keyToGet)
{
for (int i = 0; i < 1000; i++)
{
Index thisIndex = *map[i];
if (thisIndex.key == keyToGet)
{
return thisIndex.value;
break;
}
}
return -1;
}
void setValue(Map *map, int keyToSet, int valueToSet)
{
int set = 0;
for (int i = 0; i < 1000; i++)
{
Index thisIndex = *map[i];
if (thisIndex.key == keyToSet)
{
thisIndex.value = valueToSet;
set = 1;
break;
}
}
if (set == 1)
return;
for (int i = 0; i < 1000; i++)
{
Index thisIndex = *map[i];
if (thisIndex.key == -1)
{
thisIndex.key = keyToSet;
thisIndex.value = valueToSet;
break;
}
}
}
int findValue(Map *map, int valueToGet)
{
for (int i = 0; i < 1000; i++)
{
Index thisIndex = *map[i];
if (thisIndex.value == valueToGet)
return thisIndex.key;
}
return -1;
}
At some point in the code, when run, I get a SegFault, presumably for accessing or trying to write over memory over which I do not have jurisdiction. My question is, where is that happening? Which function could be doing that, and where? I've sifted through multiple times and I can't seem to find where that would be happening.
There are two major errors in your code.
First, you typedef Map to an array. That means when you have a function prototype like this:
int getValue(Map *map, int keyToGet);
you really get something like this:
int getValue(Index (*map)[1000], int keyToGet);
In C, definition mimicks use, so you should access your map elements like this:
Index thisIndex = (*map)[i];
Your way to use it, *map[i] is equivalent to *(map[i]) and requires the array to be an array of 1,000 pointers to Index, which it isn't.
The (*map)[i]sytnax complicated, and you don't need it. Because your Map is an array, it decays into a pointer to its first element. You do not need to pass a pointer to an array if you want to modify the elements. It is enough to pass a pointer to the first element, which in your case can be either of:
int getValue(Map map, int keyToGet);
int getValue(Index map[], int keyToGet);
int getValue(Index *map, int keyToGet);
Accessing the elements of the array is then just map[i].
Fixing that fixes your segmentation fault, but it doesn't fix the fact that your map doesn't work. When you assign to a struct like this:
Index thisIndex = map[i];
and then modify thisIndex, you will not modify anything in your map! Here, thisIndex is a copy. When thisIndex goes out of scope, all modifications are lost.
You can either use the map directly:
if (map[i].key == keyToSet) {
map[i].value = valueToSet;
return;
}
(and why don't you? thisIndex is longer than map[i]), or you can make thisIndex a pointer to the array element:
Index *thisIndex = &map[i];
if (thisIndex->key == keyToSet) {
thisIndex->value = valueToSet;
return;
}
Here, you access and modify the fields of map[i] through the pointer.
Hiding an array in a typedef is probably not such a good idea. Perhaps at one time you want to keep the number of active items alongside the array. (That would make your code more efficient, because you wouldn't have to traverse all 1,000 items in the worst case.) In that case, you could make Map a struct with an array of 1000 key/value pairs and a count. Then you would have to pass pointers to the struct type, so that you can update the fields. This is left as an exercise ... :)
Hello guys i have threefunctions for which i get 4 warnings...!!
The first one is this
void evaluatearxikos(void)
{
int mem;
int i;
double x[NVARS+1];
FILE *controlpointsarxika;
controlpointsarxika = fopen("controlpointsarxika.txt","r");
remove("save.txt");
for(mem = 0; mem < POPSIZE; mem++)
{
for(i = 0; i < NVARS; i++)
{
x[i+1] = population[mem].gene[i];
}
rbsplinearxiki();
XfoilCall();
population[mem].fitness = FileRead();
remove("save.txt");
}
fclose(controlpointsarxika);
}
For this one the compiler warns me tha variable x is set but not used...!! But actually i am using the variable x...!!!
The second function is this one...
void elitist(void)
{
int i;
double best,worst;
int best_mem,worst_mem;
best = population[0].fitness;
worst = population[0].fitness;
for(i = 0; i < POPSIZE - 1; i++)
{
if(population[i].fitness > population[i+1].fitness)
{
if(population[i].fitness >= best)
{
best = population[i].fitness;
best_mem = i;
}
if(population[i+1].fitness <= worst)
{
worst = population[i+1].fitness;
worst_mem = i+1;
}
}
else
{
if(population[i].fitness <= worst)
{
worst = population[i].fitness;
worst_mem = i;
}
if(population[i+1].fitness >= best)
{
best = population[i+1].fitness;
best_mem = i+1;
}
}
}
if(best >= population[POPSIZE].fitness)
{
for(i = 0; i < NVARS; i++)
{
population[POPSIZE].gene[i] = population[best_mem].gene[i];
}
population[POPSIZE].fitness = population[best_mem].fitness;
}
else
{
for(i = 0; i < NVARS; i++)
{
population[worst_mem].gene[i] = population[POPSIZE].gene[i];
}
population[worst_mem].fitness = population[POPSIZE].fitness;
}
}
For this one i get two warnings that the variables worst_mem and best_mem may be used uninitialized in this function..!! But i initialize values to both of them..!!
And the third function is this...
void crossover(void)
{
int mem,one;
int first = 0;
double x;
for(mem =0; mem < POPSIZE; mem++)
{
x = rand()%1000/1000;
if(x < PXOVER)
{
first++;
if(first%2 == 0)
{
random_Xover(one,mem);
}
else
{
one = mem;
}
}
}
}
For which i get that the variable one may be used unitialized..!! But it is initialized..!
Can you please tell me what is wrong with these functions...??
Thank you in advance
In your first function, you set (assign) x, but you never read it, hence you are not using it... you're only wasting CPU cycles by writing to it. (Note also that because you index it as i+1 you write beyond the space you've allocated for it).
In the second function, your initializations to those variables are in conditional blocks. You can see that (perhaps? I didn't verify) in all conditions they are initialized but your compiler isn't that smart.
In your third function, it does appear that one could be refered to without having first been initialized.
First: You set x but do not use it. It's a local variable that gets set but it's dropped as soon as the function returns.
Second: There might be values that makes it so that your best_mem/worst_mem never gets set in your if/else, but you are using them later on. If they haven't been set, they contain garbage if not initialized.
Third: While it shouldn't happen that you try to use an uninitialized variable in your code, it still looks weird and compiler doesn't see that it won't happen first time.
When you get compiler warnings, treat is as you are doing something wrong or rather not recommended and that it could be done in a better way.
The x variable is only used on the left hand side (i.e. assigned a value). You are not using that value on the right hand side or pass it to a function.
It may be possible to get to the end of the loop for(i = 0; i < POPSIZE - 1; i++) without those variables given a value. Why not set them in the declaration.
The call to random_Xover(one,mem); could be called when one is not set. Change the line int mem,one; to int mem,one = <some value>;
Write the definition of a function, isReverse , whose first two parameters are arrays of integers of equal size, and whose third parameter is an integer indicating the size of each array. The function returns true if and only if one array is the reverse of the other. ("Reverse" here means same elements but in reverse order.)
int isReverse(int array1[], int array2[], int size)
{
int i;
for (i=0;i<size;i++)
{
if(array1[i] == array2[size-1])
return 0;
else
return 1;
}
}
i keep getting an error. whats wrong with it.
When you return from within any block in the function the function execution ends there, so in your case you are returning from function even when the first elements of the arrays are matching which is not correct, you should check whole array and then return from the function in the end, check the code below:
int isReverse(int array1[], int array2[], int size)
{
int i,status=1;
for (i=0;i<size;i++) //Size is the length of the array? if yes than you need -1 from it.
{
if(array1[i] == array2[size])
{
status=0;
--size;
}
else
return 1;
}
return status;
}
Moreover, size-1 does not change the value of the variable size itself hence size will remain same throughout the loop, use --size this will decrement the value of actual variable hence decrementing it by one every time.
The variable "size" never changes, so you're always checking elements of array1 against the last element of array2.
Since this sounds like a homework problem, I'll let you see if you can go from there.
This is how I did it.
int isReverse(int array1[], int array2[], int SIZE)
{
for( int counter = 0; counter <= SIZE/2; counter++ )
if(array1[counter] != array2[SIZE-counter] || array2[counter] != array1[SIZE-counter])
return 1;
return 0;
}
You are just comparing the value at index i with a constant SIZE-1. Instead you want to compare the value at i with the comparison array's size-i. So each time the counter increments it compares with the opposite array's size-i. And you only have to do this for half of the array.
The return value is wrong because you are checking only 1 value from each array, not all of them. What you want to do is something like this.
for (i=0;i<size;i++)
{
if(!(array1[i] == array2[size-i-1]))
return 0;
}
return 1;
Basically you go through the array one by one, if any of the values are not the same as the appropriate value on the other array, it is not a reverse, so we return 0. If we get out of the for loop without going through the if, it means they are reverses so we return 1.
int isReverse(int array1[], int array2[], int size)
{
int flag = 0;
for (int i=0;i<size;i++)
{
if(array1[i] != array2[size-1]){
flag = 1;
break;
}
return flag;
}
}
In the code you have kept the return statement inside the loop... keep the return statement outside the loop and try
int isReverse(int a[], int b[], int n)
{
int i = 0;
while (i<n)
{
if (a[i] != b[n-i-1]) {return 0; break;}
else i++;
}
return 1;
}
anw this was the correct answer.
bool isReverse(int array1[], int array2[],int size)
{
int i=0;
for (int k=0;k<size;k++){
if (array1[k]==array2[size-k-1]){
i++;
}
}
if (i==size){
return true;
}else{
return false;
}
}