I am new to C++, I have a problem with sorting an array that has random value generated by rand() function.
The array length is 100 and the value was filled by a random number from 0 to 9 (0,1,2,3,4,5,6,7,8,9).
I have already succeed on determining the array's value, but still failed when I want to sort the array based on it's value ascendingly. By this, it means that when I print the array value, it may not be sorted by it's index, but by it's value.
Like this:
X[10]=0;
X[1]=1;
X[60]=2; ... etc until X[99]=...
Here is code to determine the value and sort it, what I have wrong here? Please help..
int length= 100;
X = new int[length];
int i;
int j;
int temp;
//determining the array value
for (i = 0; i < length; i++) {
X[i] = rand() % 10;
}
//sorting
for (i = 0; i < length; i++) {
for (j = 0; j < length; j++) {
if (X[i] < X[j]) {
temp = X[j];
X[j] = X[i];
X[i] = temp;
}
}
}
//print the array
for (i = 0; i < length; i++) {
cout << "X[" << i << "] = " << X[i] << "\n";
Sleep(10);
}
Code above won't print the sorted by value, it printed the array sorted by it's index ascendingly, not by it's value like what I want above.
Please hand me solution to this,
Thanks in advance
You are trying to initialize and sort the array in the same loop.
-First initialize the array:
for (i = 0; i < length; i++) {
X[i] = rand() % 10;
}
-Then sort the array: (Below sorting method is insertion sort, if you want to speed the process you can use counting sort since the array only contains numbers.)
for (i = 0; i < length; i++) {
for (j = i+1; j < length; j++) {
if (X[i] > X[j]) {
temp = X[j];
X[j] = X[i];
X[i] = temp;
}
}
}
Related
Below is my c++ code. I am trying to implement a selection sort using pointers (start and end). The code compiles, but I am getting a segmentation fault before it will sort the random generated list (currently only prints the random numbers).
Any help as to why this is and how to fix it would be greatly appreciated.
#include<stdio.h>
#include<stdlib.h>
#include <iostream>
using namespace std;
void selectionSort(int *start, int *stop) {
for (int i = *start; i < *stop - 1; ++i) {
int min = i;
for (int j = i + 1; j < *stop; ++j) {
if ((&start[0])[j] < (&start[0])[min])
min = j;
}
swap((&start[0])[i], (&start[0])[min]);
}
}
int main()
{
int size = 10;
int* data = new int[size];
for (int i = 0; i < size; ++i)
{
data[i] = rand() % size;
}
for (int k = 0; k < size; k++)
{
cout << data[k] << " ";
}
cout << endl;
selectionSort(data, data+size);
for (int j = 0; j < size; j++)
{
cout << data[j+1] << " ";
}
return 0;
}
The general logic in your function is in the right direction. However, you seem to be confused between values of the elements of the array and the indexing used to access the elements of the array.
The line
for (int i = *start; i < *stop - 1; ++i)
shows the first signs of the confusion.
You are initializing i with the value of the first element of the array and incrementing the value in the subsequent iterations of the loop. That is not correct. Incrementing the value of the first element of the array does not make logical sense.
*stop causes undefined behavior since stop points to a place one past the last valid element.
You need to use int* i, int* j, and int* min to properly sort the elements. That also means updating almost the entire function accordingly. Here's an updated function that works for me.
void selectionSort(int *start, int *stop) {
for (int* i = start; i < (stop - 1); ++i) {
int* min = i;
for (int* j = i + 1; j < stop; ++j) {
if (*j < *min)
{
min = j;
}
}
swap(*i, *min);
}
}
Also, the following lines in main are not correct. You end up accessing the array using an out of bounds index.
for (int j = 0; j < size; j++)
{
cout << data[j+1] << " ";
}
Replace them by
for (int k = 0; k < size; k++)
{
cout << data[k] << " ";
}
Find out the maximum sub-array of non negative numbers from an array.
The sub-array should be continuous. That is, a sub-array created by choosing the second and fourth element and skipping the third element is invalid.
Maximum sub-array is defined in terms of the sum of the elements in the sub-array. Sub-array A is greater than sub-array B if sum(A) > sum(B).
This is my solution:
vector<int> Solution::maxset(vector<int> &A) {
// Do not write main() function.
// Do not read input, instead use the arguments to the function.
// Do not print the output, instead return values as specified
// Still have a doubt. Checkout www.interviewbit.com/pages/sample_codes/ for more details
vector <int> bla;
int sum[100]={0};
int k = 0;
int j = 1;
for (int i =0; i < A.size(); i++){
if (A[i] > -1){
sum[k] = A[i] + sum[k];
}
else {
k++;
}
}
cout<<sum[0]<<" ";
cout<<sum[1]<<" ";
cout << sum[2] << " ";
int s = 0;
for (int i =0; i< 100; i++){
if (s < sum[i]){
s = sum[i];
k = i;
}
}
cout << s;
int count = 0;
for (int i =0; i < A.size(); i++){
if (A[i] < 0) {
count ++;
}
if (count == k) {
int j = i+1;
int x = 0;
while (A[j] > 0 && j< (A.size()-1)) {
// bla[x] = A[j];
x++;
j++;
}
}
}
return bla;
}
If I uncomment the line bla[x] = A[j], I get segmentation error. Can someone explain how to undetstand this error? I read it somewhere that there is not enough space in stack. I do not understand how.
Thank you
You can pass the size to a vector object or you can call it's default constructor which creates a vector object with 0 size.
std::vector<int> vecInt(10);
for(int i(0); i < vecInt.size(); i++)
vecInt[i] = i;
Or you can declare a vector with size 0:
std::vector<int> vecInt;
vecInt[0] = 10; // segfault
Because you try to store values in an un-allocated space.
To solve such problem use push_back to store and pop to clear:
So your example can be like this:
while (A[j] > 0 || j< (A.size()-1)) {
// bla[x] = A[j];
bla.push_back(A[j]);
x++;
j++;
}
I have to write a code which sort digits in one entered number.
For example: input: 4713239
output: 1233479
It doesn't work properly when I enter repeating digits(like 33) when I have the last loop as FOR:
for(int j = 0; j < arr[i]; j++) // in this loop my output is: 123479.
When I change this loop from FOR to WHILE it works properly.
It means:
while(arr[i]) // and the number is sorted correctly (1233479)
True be told, I don't know what is the difference between these operations in this code.
Why FOR loop doesn't work properly? Could somebody explain me this?
I wrote a code:
int sort(int arg)
{
int var, score = 0;
int arr[10] = {0};
for(int i = 0; i < 10; i++)
{
var = arg % 10;
arr[var]++;
arg = arg / 10;
}
for(int i = 0; i < 10; i++)
{
for(int j = 0; j < arr[i]; j++) //while(arr[i]) --> works correctly
{
score = score * 10 + i;
arr[i]--;
}
}
return score;
}
You modify both arr[i] and j, therefore the loop will end too fast when both are part of the comparison.
for(int j = 0; j < arr[i]; j++) // increase j, compare with arr[i]
{
score = score * 10 + i;
arr[i]--; // decrease arr[i]
}
That is my function:
int main() {
double data[100];
int num;
cout<<"num= ";
cin>>num;
for(int i = 1; i <= num; i++) {
cout<<i<<" element = ";
cin>>data[i];
}
Sort(data, num);
for (int i = 1; i <= num; i++) {
cout<<data[i]<<endl;
}
return 0;
}
void Sort(double data[], int n) {
int i,j,k;
double min;
for(i = 0; i < n-1; i++) {
k = i;
min = data[k];
for(j = i+1; j < n; j++)
if(data[j] < min) {
k = j;
min = data[k];
}
data[k] = data[i];
data[i] = min;
}
}
if I write for exp. three elements: 8,9,1 again cout 8,9,1?
for(int i = 1; i <= num; i++) { // WRONG
I think you mean:
for(int i = 0; i < num; i++) { // RIGHT
Arrays in C are 0-indexed remember.
Your sorting function is fine. The only problem is that you enter elements at positions 1 through n, inclusive, while you should use 0 through n-1, inclusive, in both loops of the main() function.
If you need to print numbers 1 through n, use
cout<<(i+1)<<" element = ";
You should get used of the 0 index begin in the for loop
for(int i = 0; i < N; ++i)
so fixing these two index errors will make your code run properly.
the reason is:
if you write data to data[] using 1 as the begining, your data array's first item will be a random number:
if you insert 3 elements, the array will be like this:
data[0] = ??? // maybe a very very big number
data[1] = 8
data[2] = 9
data[3] = 1
and in your Sort function, your index begins at 0 and ends before num, that means your code would only sort data[0], data[1], data[2].
if you use: num = 3, 3 2 1 as your input data for the origin code you could see that 3 and 2 is sorted
I guess your Sort code is googled from somewhere, please try to understand it.
Good online algorithm course: https://www.coursera.org/course/algs4partI
a very good algorithm online book: http://algs4.cs.princeton.edu/home/
btw, for(j = i+1; j < n; j++) in the Sort function would be better if it has { } braces.
Following this nice example I found, I was trying to create a function that dynamically generates a 2D grid (two dimensional array) of int values.
It works fairly well the first couple of times you change the values but if crashes after that. I guess the part where memory is freed doesn't work as it should.
void testApp::generate2DGrid() {
int i, j = 0;
// Delete previous 2D array
// (happens when previous value for cols and rows is 0)
if((numRowsPrev != 0) && (numColumnsPrev != 0)) {
for (i = 0; i < numRowsPrev; i++) {
delete [ ] Arr2D[i];
}
}
// Create a 2D array
Arr2D = new int * [numColumns];
for (i = 0; i < numColumns; i++) {
Arr2D[i] = new int[numRows];
}
// Assign a random values
for (i=0; i<numRows; i++) {
for (j = 0; j < numColumns; j++) {
Arr2D[i][j] = ofRandom(0, 10);
}
}
// Update previous value with new one
numRowsPrev = numRows;
numColumnsPrev = numColumns;
}
I see 1 major bug:
// Assign a random values
for (i=0; i<numRows; i++){
for (j=0; j<numColumns; j++){
Arr2D[i][j] = ofRandom(0, 10);
}
}
Here the variable 'i' is used as the first index into 'Arr2D' and goes to a max of (numRows -1)
While in this code:
for (i=0; i<numColumns; i++)
{
Arr2D[i] = new int[numRows];
}
The variable 'i' is used as the first index but goes to a max of (numColumns-1). If numRows is much larger than numColumns then we are going to have a problem.
As a side note. When you try and clean up you are leaking the columns:
if((numRowsPrev != 0) && (numColumnsPrev != 0))
{
for (i=0; i<numRowsPrev; i++){
delete [ ] Arr2D[i];
}
// Need to add this line:
delete [] Arr2D;
}
Next thing to note.
This is truly not a good idea. Use some of the provided STL classes (or potentially boost Matrix). This looks like you are binding global variables and all sorts of other nasty stuff.
2-dim array in C++ with no memory issues:
#include <vector>
typedef std::vector<int> Array;
typedef std::vector<Array> TwoDArray;
Usage:
TwoDArray Arr2D;
// Add rows
for (int i = 0; i < numRows; ++i) {
Arr2D.push_back(Array());
}
// Fill in test data
for (int i = 0; i < numRows; i++) {
for (int j = 0; j < numCols; j++) {
Arr2D[i].push_back(ofRandom(0, 10));
}
}
// Make sure the data is there
for (int i = 0; i < numRows; i++) {
for (int j = 0; j < numCols; j++) {
std::cout << Arr2D[i][j] << ' ';
}
std::cout << '\n';
}