As a practice task I have tried implementing the bubble sort algorithm using the C programming language. The following is my code:
int main() {
int arr[5];
int i, j;
int n = sizeof(arr[0]) / sizeof(arr);
srand(time(NULL));
for (i = 0; i < n; i++) {
arr[i] = rand() % 100;
}
printf("Array before ordering:\n");
for (i = 0; i < n; i++) {
printf("%d\t", arr[i]);
}
printf("\n");
for (i = 0; i < n - 1; i++) {
for (j = 0; j < n - 1; j++) {
if (arr[j] > arr[j + 1]) {
swap(&arr[j], &arr[j + 1]);
}
}
}
printf("Array after ordering:\n");
for (i = 0; i < n; i++) {
printf("%d\t", arr[i]);
}
printf("\n");
system("PAUSE");
exit(0);
}
As you can see I have two loops to print out the array, one to print out the initial array and one to print it out after ordering it. Yet this is the output:
Array before ordering:
Array after ordering:
Press any key to continue . . .
For some reason i cannot seem to output the elements of the array. I have tried running it on Visual Studio and CLion. Can anyone see what is wrong here?
int n = sizeof(arr[0]) / sizeof(arr);
This should be the other way around. i.e. sizeof(arr) / sizeof(arr[0])
If you want to debug this, try printing n.
Related
I want to randomize a to p without repetition.
int main(){
int array2[4][4];
bool arr[100]={0};
int i;
int j;
srand(time(NULL));
for(i=0; i<=3; i++){
for(j=0; j<=3; j++){
int randomNumber1;
randomNumber1 = (rand() % (82-65+1))+65;
if (!arr[randomNumber1])
{
printf("%c ",randomNumber1);
array2[i][j]=randomNumber1;
}
else
{
i--;
j--;
arr[randomNumber1]=1;
}
}
printf("\n");
}
return;
the output still has repeat alphabet. I want to have the output in 4x4 with with all a to p without it repeating.
There are some errors in your code. IMHO the most serious is that arr[randomNumber1]=1; is is the wrong branch of the test. That means that your current code does not invalidate once a number was used but only if it has already been invalidated => if you control the arr array at the end of the program all value are still 0.
That is not all. When you get a duplicate, you should only reset the inner loop, and you are currently off by 2 in your maximum ascii code: you go up to R when you want to stop at P.
Your code should be:
for (i = 0; i <= 3; i++) {
for (j = 0; j <= 3; j++) {
int randomNumber1;
randomNumber1 = (rand() % (81 - 65)) + 65;
if (!arr[randomNumber1])
{
printf("%c ", randomNumber1);
array2[i][j] = randomNumber1;
arr[randomNumber1] = 1;
}
else
{
//i--;
j--;
}
}
printf("\n");
}
But this kind of code is terribly inefficient. In my tests it took 30 to 60 steps to fill 16 values, because random can return duplicates. This is the reason why you were advised in comments to use instead the modern algorithm for Fisher-Yates shuffle:
int main() {
int array2[16];
unsigned i, j, k=0;
// initialize array with alphabets from A to P
for (i = 0; i < sizeof(array2); i++) {
array2[i] = 'A' + i;
}
// Use Fisher-Yates shuffle on the array
srand(time(NULL));
for (i = 15; i > 0; i--) {
j = rand() % (i + 1);
if (j != i) {
int c = array2[i];
array2[i] = array2[j];
array2[j] = c;
}
}
// Display a 4x4 pattern
for (i = 0; i < 4; i++) {
for (j = 0; j < 4; j++) {
printf("%c ", array2[k++]);
}
printf("\n");
}
return 0;
}
Which shuffles the array in only 16 steps.
Here is the outline
// Need some #includes here - exercise for the reader
char items[] = "abcdefghijklmnopqrstuvwxyz";
int len = sizeof(items);
srand(time(NULL));
while (len > 0) {
int r = rand() % len;
printf("%c", items[r]);
len--;
items[r] = items[len];
}
This should do the trick to print the whole alphabet in random order without repeats. Modify to do what you need it to do
I am writing a program which determines the intersection of 2 integer arrays (size of 10 elements). I think I got every other parts covered except for sorting out duplicates. Does anyone know a way of checking duplicates without making a function or using an external C library?
#include <stdio.h>
#define SIZE 10
int main(void){
//Initialization
int array1[SIZE];
for (int i = 0; i < SIZE; i++)
{
printf("Input integer %d of set A: ", i + 1);
scanf("%d", &array1[i]);
}
int array2[SIZE];
for (int i = 0; i < SIZE; i++)
{
printf("Input integer %d of set B: ", i + 1);
scanf("%d", &array2[i]);
}
int intersection[SIZE];
for (int i = 0; i < SIZE; i++)
{
intersection[i] = '\0';
}
//Intersection check
for (int i = 0; i < SIZE; i++)
{
for (int j = 0; j < SIZE; j++)
{
if (array1[i] == array2[j])
{
intersection[i] = array1[i];
break;
}
}
}
//duplicate check
int count = SIZE;
for (int i = 0; i < count; i++)
{
for (int j = i + 1; j < count; j++)
{
if (intersection[i] == intersection[j])
{
for (int k = j; j < count; i++)
{
intersection[k] = intersection[k + 1];
}
count--;
}
}
}
//printing set
for (int i = 0; i < SIZE ; i++)
{
//printf("%d\n", intersection[i]);
if (intersection[i] != '\0')
{
printf("%d\n", intersection[i]);
}
}
return 0;
}
In the code above i was trying one method although it didn't work and instead made the program stuck after inputting all the elements. I am open to other methods as long it doesn't require an external library to run. Thanks
As i see it now , in the third loop where you checking your duplicates i thing that you have to increese k not i :
for (int k = j; j < count; k++), also you must decrise the size of j in your code under the count--;.So your code for checking duplicates seems right but , you want the intersection of this two arrays you made , so you dont have to check for duplicates because in the array intersection[SIZE] you will put only one number from the two arrays, so you will not have duplicates .You should check for duplicates if you wanted to make the union of this two arrays .I make some changings to your code acording what you want to create and this code here find the intersection from two arrays.Try this and delete the duplicate check because that makes your code to run to infinity . One last thing your intersection check must be replace whith this :
//Intersection check
int i = 0, j = 0,k=0; // k is for the intersection array !
while (i < SIZE && j < SIZE) {
if (array1[i] < array2[j])
i++;
else if (array2[j] < array1[i])
j++;
else if(array1[i]==array2[j]) // if array1[i] == array2[j]
{
intersection[k]=array2[j];
//printf("intersection[%d]=%d\n",i,intersection[i]);
intersectCount++;
k++;
i++;
j++;
}
}
printf("intersectCount=%d\n",intersectCount);
I have a task to sort negative and positive numbers while using dynamic memory, therefore in this case I used calloc and bubble sort to arrange negative numbers first while not changing their order. The problem is when I enter an even number of integers, in the middle of the result some random negative number of 10 digits appears. The same doesn't happen with odd number of integers. What seems to be the problem?
#include <stdio.h>
#include <stdlib.h>
#define SIZE 1000
void swap(int *arr, int n) {
int i, j, temp;
for (i = 0; i <= n; i++) {
for (j = 1; j <= n; j++) {
if (arr[j] < 0) {
temp = arr[j];
arr[j] = arr[j - 1];
arr[j - 1] = temp;
}
}
}
printf("sorted integers to negative and positive: \n");
for (i = 0; i < n; i++) {
printf("%i ", arr[i]);
}
}
int main() {
int n;
int i, *sk;
printf("Enter integer: \n");
scanf("%d", &n);
printf("Enter %i integers: \n", n);
sk = (int*)calloc(sizeof(int), n);
for (i = 0; i < n; i++) {
scanf("%d", sk + i);
}
swap(sk, n);
return 0;
}
This is undefined behavior that happens to manifest itself to you only when you happen to enter an even number of integers, but in reality the problem is always there: you read a value from one-past-the-end of the array, and it makes its way to the middle of your array.
You can fix this behavior by changing i <= n and j <= n with i < n and j < n. However, this is not going to fix your broken sorting algorithm, because the swapping condition is incorrect as well. Instead of
if(arr[j]<0)
it should be
if(arr[j]<arr[j-1])
You have 2 classic bugs in your for loops:
for (i = 0; i <= n; i++) is almost always wrong because the loop is run n + 1 times, where it should only enumerate index values from 0 to n - 1.
You have the same off by one error in the second loop: the test j <= n makes you go one step too far and read beyond the end of the array. Some random value gets shuffled into the array, but this undefined behavior could have worse consequences.
Furthermore, your comparison test is incorrect, it should be if (arr[j] < arr[j-1]).
As a rule of thumb, whenever you see the <= operator in a loop test, look again, it is probably a bug.
Here is a corrected version:
void swap(int *arr, int n) {
int i, j, temp;
for (i = 0; i < n; i++) {
for (j = 1; j < n; j++) {
if (arr[j] < arr[j - 1]) {
temp = arr[j];
arr[j] = arr[j - 1];
arr[j - 1] = temp;
}
}
}
printf("sorted integers to negative and positive: \n");
for (i = 0; i < n; i++) {
printf("%i ", arr[i]);
}
printf("\n");
}
I'm trying to sort an array size in C, i have ran some tests on it before i publish it here (I have left the testing statement in).
I get the correct answer once but than it moves the higher value into the wrong array, even though i have used an IF statement.
If you guys run the program it will make sense to you.
#include <stdio.h>
# define size 3
int sum();
main() {
int a[size] = { 4, 2, 3 };
int temp, i, j, x;
for (j = 0; j < size; j++){
for (i = 1; i < size; i++){
for (x = 0; x < size; x++){
printf("%d", a[x]); //testing statement;
}
printf("\n");
if (a[j] > a[i]){
temp = a[j];
a[j] = a[i];
a[i] = temp;
}
}
}
for (x = 0; x < size; x++){
printf("%d", a[x]);
}
getch();
}
Change
for (i = 1; i < size; i++){
to something like
for (i = j + 1; i < size; i++) {
and your sort will work correctly. As it is, you're comparing the elements again with if (a[j] > a[i]){ which can move them back when you reset i to 1.
Hello i am trying to use counting sort to sort numbers that i read from a file. this is my code:
void CountingSort(int array[], int k, int n)
{
int i, j;
int B[100], C[1000];
for (i = 0; i <= k; i++)
{
C[i] = 0;
}
for (j = 1; j <= n; j++)
{
C[array[j]] = C[array[j]] + 1;
}
for (i = 1; i <= k; i++)
{
C[i] = C[i] + C[i-1];
}
for (j = 1; j <= n; j++)
{
B[C[array[j]]] = array[j];
C[array[j]] = C[array[j]] - 1;
}
printf("The Sorted array is : ");
for (i = 1; i <= n; i++)
{
printf("%d ", B[i]);
}
}
void max(int array[],int *k,int n){
int i;
printf("n je %d\n",n);
for (i = 0; i < n; i++)
{
if (array[i] > *k) {
*k = array[i];
}
}
}
int main(int brArg,char *arg[])
{
FILE *ulaz;
ulaz = fopen(arg[1], "r");
int array[100];
int i=0,j,k=0,n,x,z;
while(fscanf(ulaz, "%d", &array[i])!=EOF)i++;
fclose(ulaz);
n=i;
max(array,&k,n);
printf("Max je %d\n",k);
CountingSort(array,k,n);
return 0;
}
i have no errors but when i start my program i get Segmentation fault error. pls help! (dont read this bot is asking me to write some more details but i have none so i just write some random words so i can post my question and hopefully get an answer)
The problem is that your implementation of the counting sort is incorrect: it uses arrays as if they were one-based, while in C they are zero-based.
After carefully going through your loops and fixing all situations where you use a for loop that goes 1..k, inclusive, instead of the correct 0..k-1, the code starts to work fine:
int i, j;
int B[100], C[1000];
for (i = 0; i <= k; i++){
C[i] = 0;
}
for (j = 0; j < n; j++){
C[array[j]]++;
}
for (i = 1; i <= k; i++){
C[i] += C[i-1];
}
for (j = 0; j < n; j++) {
B[--C[array[j]]] = array[j];
}
printf("The Sorted array is : ");
for (i = 0; i < n; i++) {
printf("%d ", B[i]);
}
Demo.
Note: I modified some of the operations to use C-style compound assignments and increments/decrements, e.g. C[array[j]]++ in place of C[array[j]] = C[array[j]] + 1 etc.
The problem most likely is here
int B[100], C[1000]; // C has space for numbers up to 999
...
for (i = 1; i <= k; i++)
C[i] = C[i] + C[i-1]; // adding up till C[k] == sum(array)
for (j = 0; j < n; j++)
B[C[array[j]]] = array[j]; // B has space up to 99, but C[k] is sum(array)
so you're reserving space for C for a highest value of 999 but in B you're assuming that the sum of all input values is less than 100...
the resolution of your problem is to first probe the input array and get the maximum and the sum of all input values (and minimum if the range may be negative) and allocate space accordingly
edit: you probably meant j < n and not j <= n
Adding to dasblinkenlight's spot-on answer:
Is your input data guaranteed to be in the range [0, 999]? If it isn't, it's obvious that segmentation faults can and will occur. Assume that the maximum value of array is 1000. C is declared as
int C[1000];
which means that C's valid indices are 0, 1, 2, ... 999. But, at some point, you will have the following:
C[array[j]] = ... /* whatever */
where array[j] > 999 so you will be attempting an out-of-bounds memory access. The solution is simple: probe array for its maximum value and use dynamic memory allocation via malloc:
/* assuming k is the maximum value */
int * C = malloc((k + 1) * sizeof(int));
Note: an alternative to this, which would also nullify the need for an initialization loop to make all elements of C equal to 0, would be to use calloc, which dynamically allocates memory set to 0.
// allocate C with elements set to 0
int * C = calloc(k + 1, sizeof(int);
Another important factor is the range of your running indices: you seem to have forgotten that arrays in C are indexed starting from 0. To traverse an array of length K, you would do:
for (i = 0; i < K; ++i)
{
processArray(array[i]);
}
instead of
for (i = 1; i <= K; ++i)
{
processArray(array[i]);
}