My goal is to have a player input a bunch of numbers for an array then that array is written into a text file. Another part of it is to be able to receive a bunch of numbers from a text file and put them into a sorted array of highest to lowest then output that array. But for some reason, I'm getting a lot of errors, ones that i feel like with some research I can fix. Unfortunately, there is one very confusing situation where I test to make sure the unsorted array is correct by outputting each element of the array. This is not a part of the final program but a test for now. I have a for loop that does so and it works perfectly, outputting each number as expected. Then in the next for loop, the exact same thing is supposed to happen but the numbers being outputted are all messed up. I do not understand how. Code below
void readFile(string fName) {
string fileName = fName + ".txt";
ifstream myFile(fileName);
char c;
string num;
int count = 0;
// Bring the array from file to int array
while (!myFile.eof()) {
myFile.get(c);
if (isspace(c) && num != "") {
int n = stoi(num);
intArray[count] = n;
count++;
num = "";
continue;
}
if (!myFile.eof()) {
num += c;
}
}
for (int i = 0; i < 10; i++) {
cout << intArray[i] << endl;
}
// Sort the array higest to lowest
for (int i = 0; i < 10; i++) {
cout << intArray[i] << " ";
for (int j = 9; j >= i; j--) {
if (j == 0) {
continue;
}
if (intArray[j] > intArray[j - 1]) {
int temp = arr[j];
intArray[j] = intArray[j - 1];
intArray[j - 1] = temp;
}
}
cout << endl;
}
}
sorry about the formatting above, its being weird so imagine the code is within the function.
This is what this outputs:
1
2
3
4
5
6
7
8
99
234
1
1
1
1
1
1
1
1
1
1
The numbers before the series of 1's is the actual array, the 1's is what is apparently the array according the cout in the last section of code where it says cout << intArray[i]
Your array does appear to be sorted. The reason for all the ones being printed is due to the location of the cout << within the outer loop.
Consider what your array looks like after your first iteration through the inner loop:
234,1,2,3,4,5,6,7,8,99
Now consider that you've incremented i to 1 in the outer loop. When you index your array intArray[i], the ith element is now 1 because you correctly moved it there. Each time, you're moving your smaller elements up one position in the array, then indexing to the position where the 1 is.
Don't try to print the sorted array while you're sorting it. Instead loop over it and print it after the sort.
Related
I am having trouble understanding why this exception is being thrown. I allocated an array to receive 100 int values and want to store all odd numbers under 200 into the array (which should be 100 integer values). I'm trying to understand why my code is not working.
I have called my function to allocate an array of 100 int values. After, I created a for-loop to iterate through and store integers into the array however I created an if statement to only store odd numbers. What I can't understand is if I put my counter to 200 and use the if statement an exception is thrown, but if I don't insert the if statement and only put my counter to 100 all numbers between 1-100 stored and an exception won't be thrown.
The only thing I can think of that's causing this is when my counter is at 200 and I have the if statement to catch all odd number, somehow all numbers under 200 are being stored in the array causing the exception to be thrown.
int *allocIntArray(int);
int main() {
int *a;
a = allocIntArray(100);
for (int count = 1; count < 200; count++) {
if (a[count] % 2 == 1) {
a[count] = count;
cout << a[count] << endl;
}
}
delete[] a;
return 0;
}
int *allocIntArray(int size) {
int *newarray = new int[size]();
return newarray;
}
When I look at the program output, it only displays the odd numbers yet the exception is being thrown. That tells me my if statement is working yet something is being muddied up.
What am I missing?
Thanks for your time and knowledge.
Cause of the error
If you have an array a that was created with n elements, it is undefined behavior when trying to access an array element out of bouds. So the index MUST always be between 0 and n-1.
So the behavior of your program is undefined as soon as count is 100, since evaluating the condition in the if-clause already tries to access out of bounds.
Adjustment that does what you want
Now in addition, there is a serious bug in your program logic: If you want to add numbers that satisfy some kind of condition, you need 2 counters: one for iterating on the numbers, and one for the last index used in the array:
for (int nextitem=0, count = 1; count < 200; count++) {
if (count % 2 == 1) { // not a[count], you need to test number itself
a[nextitem++] = count;
cout << count << endl;
if (nextitem == 100) { // attention: hard numbers should be avoided
cout << "Array full: " << nextitem << " items reached at " << count <<endl;
break; // exit the for loop
}
}
}
But, this solution requires you to keep track of the last item in the array, and the size of the array (it's hard-coded here).
Vectors
You are probably learning. But in C++ a better solution would be to use vector instead of an array, and use push_back(). Vectors manage the memory, so that you can focus on your algorithm. The full program would then look like:
vector<int> a;
for (int count = 1; count < 200; count++) {
if (count % 2 == 1) {
a.push_back(count);
cout << count << endl;
}
}
cout << "Added " << a.size() << " elements" <<endl;
cout << "10th element: "<< a[9] << endl;
The problem is not how many numbers you're storing but where you're storing them; you're storing 101 in a[101], which is obviously wrong.
If the i:th odd number is C, the correct index is i-1, not C.
The most readable change is probably to introduce a new counter variable.
int main() {
int a[100] = {0};
int count = 0;
for (int number = 1; number < 200; number++) {
if (number % 2 == 1) {
a[count] = number;
count += 1;
}
}
}
I think transforming this from a search problem to a generation problem makes it easier to get right.
If you happen to remember that every odd number C can be written on the form 2 * A + 1for some A, you' will see that the sequence you're looking for is
2*0+1, 2*1+1, 2*2+1, ..., 2*99+1
so
int main()
{
int numbers[100] = {0};
for (int i = 0; i < 100; i++)
{
numbers[i] = 2 * i + 1;
}
}
You can also go the other way around, looping over the odd numbers and storing them in the right place:
int main()
{
int numbers[100] = {0};
for (int i = 1; i < 200; i += 2) // This loops over the odd numbers.
{
numbers[i/2] = i; // Integer division makes this work.
}
}
I'm a Computer Science student. This is some code that I completed for my Data Structures and Algorithms class. It compiles fine, and runs correctly, but there is an error in it that I corrected with a band-aid. I'm hoping to get an answer as to how to fix it the right way, so that in the future, I know how to do this right.
The object of the assignment was to create a binary search. I took a program that I had created that used a heap sort and added a binary search. I used Visual Studio for my compiler.
My problem is that I chose to read in my values from a text file into an array. Each integer in the text file is separated by a tabbed space. In line 98, the file reads in correctly, but when I get to the last item in the file, the counter (n) counts one time too many, and assigns a large negative number (because of the array overflow) to that index in the array, which then causes my heap sort to start with a very large negative number that I don't need. I put a band-aid on this by assigning the last spot in the array the first spot in the array. I have compared the number read out to my file, and every number is there, but the large number is gone, so I know it works. This is not a suitable fix for me, even if the program does run correctly. I would like to know if anyone knows of a correct solution that would iterate through my file, assign each integer to a spot in the array, but not overflow the array.
Here is the entire program:
#include "stdafx.h"
#include <iostream>
#include <fstream>
using std::cout;
using std::cin;
using std::endl;
using std::ifstream;
#define MAXSIZE 100
void heapify(int heapList[], int i, int n) //i shows the index of array and n is the counter
{
int listSize;
listSize=n;
int j, temp;//j is a temporary index for array
temp = heapList[i];//temporary storage for an element of the array
j = 2 * i;//end of list
while (j <= listSize)
{
if (j < listSize && heapList[j + 1] > heapList[j])//if the value in the next spot is greater than the value in the current spot
j = j + 1;//moves value if greater than value beneath it
if (temp > heapList[j])//if the value in i in greater than the value in j
break;
else if (temp <= heapList[j])//if the value in i is less than the value in j
{
heapList[j / 2] = heapList[j];//assigns the value in j/2 to the current value in j--creates parent node
j = 2 * j;//recreates end of list
}
}
heapList[j / 2] = temp;//assigns to value in j/2 to i
return;
}
//This method is simply to iterate through the list of elements to heapify each one
void buildHeap(int heapList[], int n) {//n is the counter--total list size
int listSize;
listSize = n;
for (int i = listSize / 2; i >= 1; i--)//for loop to create heap
{
heapify(heapList, i, n);
}
}
//This sort function will take the values that have been made into a heap and arrange them in order so that they are least to greatest
void sort(int heapList[], int n)//heapsort
{
buildHeap(heapList, n);
for (int i = n; i >= 2; i--)//for loop to sort heap--i is >= 2 because the last two nodes will not have anything less than them
{
int temp = heapList[i];
heapList[i] = heapList[1];
heapList[1] = temp;
heapify(heapList, 1, i - 1);
}
}
//Binary search
void binarySearch(int heapList[], int first, int last) {//first=the beginning of the list, last=end of the list
int mid = first + last / 2;//to find middle for search
int searchKey;//number to search
cout << "Enter a number to search for: ";
cin >> searchKey;
while ((heapList[mid] != searchKey) && (first <= last)) {//while we still have a list to search through
if (searchKey < heapList[mid]) {
last = mid - 1;//shorten list by half
}
else {
first = mid + 1;//shorten list by half
}
mid = (first + last) / 2;//find new middle
}
if (first <= last) {//found number
cout << "Your number is " << mid << "th in line."<< endl;
}
else {//no number in list
cout << "Could not find the number.";
}
}
int main()
{
int j = 0;
int n = 0;//counter
int first = 0;
int key;//to prevent the program from closing
int heapList[MAXSIZE];//initialized heapList to the maximum size, currently 100
ifstream fin;
fin.open("Heapsort.txt");//in the same directory as the program
while (fin >> heapList[n]) {//read in
n++;
}
heapList[n] = heapList[0];
int last = n;
sort(heapList, n);
cout << "Sorted heapList" << endl;
for (int i = 1; i <= n; i++)//for loop for printing sorted heap
{
cout << heapList[i] << endl;
}
binarySearch(heapList, first, last);
cout << "Press Ctrl-N to exit." << endl;
cin >> key;
}
int heapList[MAXSIZE];//initialized heapList to the maximum size, currently 100
This comment is wrong - heapList array is declared not initialized, so when you had read all data from the file, index variable n will point to the uninitialized cell. Any attempt to use it will invoke an undefined behavior. You could either: initialize an array before using it, decrement n value, since it greater than read values number by one, or better use std::vector instead of array.
You populate values for heapsort for indices 0 to n-1 only.
Then you access heaplist from 1 to n which is out of bounds since no value was put in heapsort[n].
Use
for (int i = 0; i < n; i++) //instead of i=1 to n
I'm trying to use a bubble sort to sort an array of 10 numbers. The program asks for 10 numbers from the user then outputs the unsorted array. This part works fine. It then runs a bubble sort and outputs the sorted array. In my tests I only entered positive integers, however the first value in the sorted array is always a really small number expressed like "2.6812368e-317" or something similar. The rest of the values in the array then appear after that number sorted as they should be. After the sorted array displays Windows then comes up with an error saying the program has stopped working.
My code is as follows:
int main(int argc, char** argv) {
double arrSort[10];// declare array to store numbers to be sorted
cout << "Please enter 10 numbers to be sorted" << endl;
// ask for values from user and input them in array
for (int i = 0; i < 10; i++)
{
cin >> arrSort[i];
}
// display unsorted array
cout << "Unsorted Array: " << endl;
for (int i = 0; i < 10; i++)
{
if (i < 9)
cout << arrSort[i] << ", ";
else
cout << arrSort[i] << endl;
}
bool changed = true; // variable to store whether a change has been made
double temp; // variable to temporarily store a value while swapping
//start looping the array
do
{
changed = false; // change to false so that if no changes are made to array the loop exits
for (int i = 0; i < 10; i++) // start loop within array to check values
{
if (arrSort[i] > arrSort[i + 1]) // check if current index is greater than next index
{
// swap values
temp = arrSort[i]; // store current index in temp variable
arrSort[i] = arrSort[i + 1]; // assign next index to current index
arrSort[i + 1] = temp; // assign temp value to next index
changed = true; // set changed to true to run another loop
}
}
}while (changed); // if array was changed loop through again, if not changed exit loop
// output results of sorted array
cout << "Sorted Array: " << endl;
for (int i = 0; i < 10; i++)
{
if (i < 9)
cout << arrSort[i] << ", ";
else
cout << arrSort[i] << endl;
}
return 0;
}
Here is a screenshot of a test run of the program:
Sorted Array output
for (int i = 0; i < 10; i++) // <-- here's problem.
{
if (arrSort[i] > arrSort[i + 1])
{
// swap values
}
}
i variable should be less than 9 not 10. As you can see in if statement you are checking arrSort[i + 1], so in last element you are checking number which is out of your table range (arrSort[10] doesn't exist). I'm not able to check it right now, but I guess it's the problem.
I think the problem is here:
if (arrSort[i] > arrSort[i + 1])
When
i=9
Your array have 10 elements and you try to compare
arrSort[9] > arrSort[9+1]
And
arrSort[10]
Does not exist
So, I tried to make an array using input first, then sorting it out from smallest to biggest, then display the array to monitor.
So I come up with this code :
#include <iostream>
using namespace std;
void pancakeSort(int sortArray[], int sortSize);
int main()
{
// Input The Array Element Value
int pancake[10];
for(int i=0; i<10; i++)
{
cout << "Person " << i+1 << " eat pancakes = ";
cin >> pancake[i];
}
// call pancake sorting function
pancakeSort(pancake, 10);
}
void pancakeSort(int sortArray[], int sortSize)
{
int length = 10;
int temp;
int stop = 10;
// this is where the array get sorting out from smallest to biggest number
for(int counter = length-1; counter>=0; counter--)
{
for(int j=0; j<stop; j++)
{
if(sortArray[j]>sortArray[j+1])
{
temp = sortArray[j+1];
sortArray[j+1] = sortArray[j];
sortArray[j]=temp;
}
}
stop--;
}
// after that, the array get display here
for(int x=0; x<sortSize; x++)
{
cout << sortArray[x] << " ";
}
}
but the output is weird :
enter image description here
the function is successfully sorting the array from smallest to biggest,
but there is 2 weird things :
1. The biggest value element (which is 96 from what I input and it's the 10th element after got sorted out), disappear from the display.
2. For some reason, there is value 10 , which I didn't input on the array.
So, what happened?
In the loop
for(int j=0; j<stop; j++)
{
if(sortArray[j]>sortArray[j+1])
{
temp = sortArray[j+1];
sortArray[j+1] = sortArray[j];
sortArray[j]=temp;
}
}
stop is the length of the array, and you are iterating through values of j = 0 to stop - 1. When j reaches stop - 1, the next element that is j+1 becomes stop (10 in this case). But since your array has a length of 10, sortArray[10] is not part of the array, but is referring to some other object in memory which is usually a garbage value. The garbage value is 10 in this case. When you swap sortArray[10] and sortArray[9], the garbage value becomes part of the array and the value at index 9 leaves the array. This keeps on happening till the outer loop ends.
The end result is that unless the garbage value < largest element in the array, the garbage value is pushed in the array and the greatest value of the array is put at sortArray[10] which is not part of the array. If the garbage value is greater than all the values of the array, it'll be found at sortArray[10] which is again not part of the array and your code will return the desired result.
Essentially, what you are doing is giving the function an array of 10 (or stop) elements, but the function is actually working with an array of 11 (or stop + 1) elements, with the last element being a garbage value. The simple fix is to change the conditional of the loop to j < stop - 1.
Note that if you had written this code in a managed (or a comparatively higher level) language like Java or C#, it would have raised an IndexOutOfBoundsException.
At index 9, j+1 is out of bounds. So to fix this, you only need to check till index 8
for(int counter = length-1; counter>=0; counter--)
{
for(int j=0; j<stop-1; j++)
{
if(sortArray[j]>sortArray[j+1])
{
temp = sortArray[j+1];
sortArray[j+1] = sortArray[j];
sortArray[j]=temp;
}
}
stop--;
}
Look carefully at the inner loop condition j<stop-1
I am attempting to fill an array backwards from 20 to 0 but whenever I print it out it still prints out forwards. For instance I want to put in 1,2,3,4,5 and have it come out as 5,4,3,2,1.
I have attempted to do a for loop that counts backwards from 20 to 0 but when i print it it is still coming out incorrect. Any help?
int temp;
for (int i = 20; i > 0; i--)
{
cout << "Please enter the next number. Use a -1 to indicate you are done: ";
cin >> temp;
while(temp > 9 || temp < -2)
{
cout << "You may only put numbers in 0 - 9 or -1 to exit. Please enter another number: ";
cin >> temp;
}
arr1[i] = temp;
cout << arr1[i];
}
for (int i = 21; i > 0; i--)
{
cout << arr1[i];
What's the size of your array?
Assume that the size is 21 (indexes from 0 to 20).
First of all please note that your first loop will never populate the array at index 0 (something like this arr1[0] = temp will never be executed inside your first loop).
If you want to avoid this behavior you should write your first for loop like this:
for (int i = 20; i >= 0; i--){...}.
The second for loop has some issues:
You are traversing the array backwards while you want to do the opposite.
The loop starts from an index out of bound (21).
The loop may print some undefined values (You should remember the index of the last added value).
I suggest you to use other data structures like a Stack but if you want to use an array you can edit your code as follows:
int i;
for (i = 20; i >= 0; i--){...}
for (i; i <= 20; ++i) { cout << arr1[i]; }
If you don't want to declare int i; outside of the loop you can do something like that:
int lastAdded;
for (int i = 20; i >= 0; i--){
...
lastAdded = i;
}
for (int i = lastAdded; i <= 20; i++) { cout << arr1[i]; }
Edit: Note that neither your code nor mine stops asking for a new value after the insertion of a -1.
If you want to achieve this behavior you should use a while loop instead of the first for loop and check for the exit condition.