I wrote a multiplication table like this:
#include <iostream>
#include <conio.h>
using namespace std;
int main(){
int table[9][9], i, j;
for (i = 0; i < 10; ++i){
for (j = 0; j < 10; ++j)
{
table[i][j] = (i + 1) * (j + 1);
cout << table[i][j] << "\t";
}
cout << endl;
}
_getch();
return 0;
}
And when I run it it gives me the right answer but when I press a key it throws this error:
run time check faliure #2-stack around the variable table was corrupted
But it doesn't throw that error when I change the code to this:
......
int main(){
**int table[10][10]**, i, j;
for (i = 0; i < 10; ++i){
......
If they both give the same answer then what's the difference??
You are overflowing your arrays, The max index in bounds is 8 (since the indices are zero based and you defined 9 cells as your dimensions size so 8 will be the last cell in each dimension) and your for loop can reach till 9 (including 9) which will cause an overflow.
The snippet int table[9] declares an array of size 9, that means valid indices are actually 0-8. But your loop iterates from 0 to 9. This causes a write into an invalid memory region (which doesn't belong to your array), therefore corrupting your stack.
Now you actually have a two dimensional array, but the problem remains the same.
You're going outside the array in your for loops. They should be:
for (i = 0; i < 9; ++i){
for (j = 0; j < 9; ++j)
The array indexes run from 0 to 8, but you were going up to 9 because your conditions were i < 10 and j < 10.
Arrays in C/C++ start with 0 index.
When you declare table[9][9] you reserve memory for 9x9 array with indexes 0..8, 0..8
but in for loop your upper index is 9 - it is out of array range
I guess you should declare table like you pointed:
int table[10][10];
You are accessing out of array's range element.
Your array is a 9x9 table but you are trying to access 10x10 table.
So either use i<9 and j<9 in your both loops or increase your array size to table[10][10].
Hope this might help.
Rule of thumb: in for loops, N in (i = 0; i < N; i++) clause should (almost always) be equal to the corresponding array's length. When you see either i <= N or i < N + 1, it's (most often) a sign of the dreaded off-by-one bug.
Related
I am trying to make a program that sorts an array without using the sort function (that won't work with objects or structs). I have made the greater than one work, but the less than one keeps changing the greatest element in the array to a one and sorting it wrong, and when used with the greater than function, the first element is turned into a large number. Can someone please help me fix this or is it my compiler.
void min_sort(int array[], const unsigned int size){
for(int k = 0; k < size; k++) {
for(int i = 0; i < size; i++) {
if(array[i] > array[i+1]){
int temp = array[i];
array[i] = array[i+1];
array[i+1] = temp;
}
}
}
}
You are not looping correctly. Looks like you are trying bubble sort which is:
void min_sort(int array[], const unsigned int size){
for(int k = 0; k < size; k++)
for(int i = k+1; i < size; i++)
if(array[i] < array[k]){
int temp = array[i];
array[i] = array[k];
array[k] = temp;
}
}
void min_sort(int array[], const unsigned int size)
{
for(int i=0;i<size-1;i++)
{
for(int j=0;j<size-1-i;j++)
{
if(array[j]>array[j+1])
{
swap(array[j] , array[j+1]);
}
}
}
}
I see that you are trying to implement the bubble sort algorithm. I have posted the code for bubble sort here. In bubble sort you basically compare the element at an index j and the element next to it at index j+1. If array[j] is greater than array[j+1] , you swap them using the swap() function or by using the temp method. The outer loop will run size - 1 times , and the inner loop will run size - 1 - i times because the last element will already be in place.
For Example we have an array of size 4 with elements such as :
array[i] = [100,90,8,10]
The bubble sort will sort it in the following steps :
90,100,8,10
90,8,100,10
90,8,10,100
8,90,10,100
8,10,90,100
8,10,90,100
See, the use of size-1-i . You can see the nested loop runs less number of times in each iteration of the outer loop.
There is only one mistake that your 2nd loop condition should be: i < size -1.
So it should be:
for (int i = 0; i < size -1; i++)
Your attempt at bubble sort is basically correct, you just have an out of bounds issue with your inner loop. During the inner loop's last run, i == size - 1, therefore i + 1 is equal to size, thus data[i+1] is out of range. Simply change the condition of your for to be i < size - 1.
Working example: https://godbolt.org/z/e5ohWPfTz
I was given the integers 15, 16, 17 ,18 ,19 and 20.
I am supposed to put only the numbers divisible by 4 into a vector and then display the values in the vector.
I know how to do the problem using arrays but I'm guessing I don't know how to properly use pushback or vectors.
#include<iostream>
#include<vector>
using namespace std;
int main()
{
vector<int> arrmain; int i,j;
for (int i = 15; i <=20 ; i++)
{
//checking which numbers are divisible by 4
if (i%4 == 0)
{ //if number is divisible by 4 inserting them into arrmain
arrmain.push_back(i);
//output the elements in the vector
for(j=0; j<=arrmain.size(); j++)
{
cout <<arrmain[i]<< " "<<endl;
}
}
}
return 0;
}
wanted output: Numbers divisible by 4: 16, 20
As already mentioned in the comments, you have a couple of problems in your code.
All which will bite you in the end when writing more code.
A lot of them can be told to you by compiler-tools. For example by using -Weverything in clang.
To pick out the most important ones:
source.cpp:8:10: warning: declaration shadows a local variable [-Wshadow]
for (int i = 15; i <=20 ; i++)
and
source.cpp:6:26: warning: unused variable 'i' [-Wunused-variable]
vector arrmain; int i,j;
Beside those, you have a logical issue in your code:
for values to check
if value is ok
print all known correct values
This will result in: 16, 16, 20 when ran.
Instead, you want to change the scope of the printing so it doesn't print on every match.
Finally, the bug you are seeing:
for(j=0; j<=arrmain.size(); j++)
{
cout <<arrmain[i]<< " "<<endl;
}
This bug is the result of poor naming, let me rename so you see the problem:
for(innercounter=0; innercounter<=arrmain.size(); innercounter++)
{
cout <<arrmain[outercounter]<< " "<<endl;
}
Now, it should be clear that you are using the wrong variable to index the vector. This will be indexes 16 and 20, in a vector with max size of 2. As these indexes are out-of-bounds for the vector, you have undefined behavior. When using the right index, the <= also causes you to go 1 index out of the bounds of the vector use < instead.
Besides using better names for your variables, I would recommend using the range based for. This is available since C++11.
for (int value : arrmain)
{
cout << value << " "<<endl;
}
The main issues in your code are that you are (1) using the wrong variable to index your vector when printing its values, i.e. you use cout <<arrmain[i] instead of cout <<arrmain[j]; and (2) that you exceed array bounds when iterating up to j <= arrmain.size() (instead of j < arrmain.size(). Note that arrmain[arrmain.size()] exceeds the vector's bounds by one because vector indices are 0-based; an vector of size 5, for example, has valid indices ranging from 0..4, and 5 is out of bounds.
A minor issue is that you print the array's contents again and again while filling it up. You probably want to print it once after the first loop, not again and again within it.
int main()
{
vector<int> arrmain;
for (int i = 15; i <=20 ; i++)
{
//checking which numbers are divisible by 4
if (i%4 == 0)
{ //if number is divisible by 4 inserting them into arrmain
arrmain.push_back(i);
}
}
//output the elements in the vector
for(int j=0; j<arrmain.size(); j++)
{
cout <<arrmain[j]<< " "<<endl;
}
return 0;
}
Concerning the range-based for loop mentioned in the comment, note that you can iterate over the elements of a vector using the following abbreviate syntax:
// could also be written as range-based for loop:
for(auto val : arrmain) {
cout << val << " "<<endl;
}
This syntax is called a range-based for loop and is described, for example, here at cppreference.com.
After running your code, I found two bugs which are fixed in code below.
vector<int> arrmain; int i, j;
for (int i = 15; i <= 20; i++)
{
//checking which numbers are divisible by 4
if (i % 4 == 0)
{ //if number is divisible by 4 inserting them into arrmain
arrmain.push_back(i);
//output the elements in the vector
for (j = 0; j < arrmain.size(); j++) // should be < instead of <=
{
cout << arrmain[j] << " " << endl; // j instead of i
}
}
}
This code will output: 16 16 20, as you are printing elements of vector after each insert operation. You can take second loop outside to avoid doing repeated operations.
Basically, vectors are used in case of handling dynamic size change. So you can use push_back() if you want to increase the size of the vector dynamically or you can use []operator if size is already predefined.
The output is a string of numbers of entire row/column instead of a single number. Can someone please help me in this?
int main() {
/* Enter your code here. Read input from STDIN. Print output to STDOUT */
int t;
cin>>t;
while(t--){
int n,m,cnt=0;
cin>>n>>m;
for(int i=0;i<=n+1;i++){
for(int j=0;j<=m+1;j++){
if(i==0||i==n+1||j==m+1||j==0) G[i][j]=0;
cin>>G[i][j];
}
}
cout<<G[1][2]<<endl;//this gives wrong o/p
return 0;
}
Most likely you are reading out of bounds due to a i <= n + 1 and j <= m + 1 conditions in your for loops thus invoking undefined behavior resulting in a corrupted stack which explains the output you are seeing. Modify the boundaries to:
i < n and j < m. Arrays are zero indexed in C++. First array element is accessed via somearray[0] and the last element is somearray[n-1] not somearray[n] which is what you are trying to access in your code. The same goes for multi-dimensional arrays. The statement of:
cout << G[i][j] << endl;
is wrongly placed outside the for loops. It should be inside the inner for loop. The array should be defined as a second statement in your while loop:
int G[n][m]; // Avoid VLAs
That being said variable length arrays are not part of the C++ standard and you should prefer std::vector and std::array to raw arrays.
Assuming G is a 2D array of size n x m, then you go out of bounds here:
for(int i=0;i<=n+1;i++) {
for(int j=0;j<=m+1;j++)
since array indexing starts from 0, and ends at size - 1.
As a result, your code invokes Undefined Behavior. To avoid that, simply change your double for loop to this:
for(int i = 0; i < n; i++) {
for(int j = 0;j < m; j++)
I am trying to create a 3-Dimensional array which gets filled up with pseudo-random numbers ranging from 0 to 9 (inclusive). This is my first time working with arrays containing more than 2 dimensions, so I am a bit lost.
At first the only number being inputted into the array was a 1, but after changing some code around, every number but the last one is a 1, and the last digit is pseudo-random. To make matters worse with the new situation I am in, when I hit enter, I get a weird error message.
Besides these two errors (error filling up array, and debug error), I also cannot figure out how in the world to print it out in 3 groups of 3 x 3 numbers, although right now, that is a lower issue on my agenda (although hints for that would be appreciated).
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int main(){
srand(time(NULL));
const int arrayRow = 3, arrayColumns = 3, arrayDepth = 3;
int fun[arrayRow][arrayColumns][arrayDepth];
for (int r = 0; r < 4; r++){
for (int c = 0; c < 4; c++){
for (int d = 0; d < 4; d++){
int value = rand() % 10;
fun[r][c][d] = value;
cout << fun[arrayRow][arrayColumns][arrayDepth];
}
}
}
cout << "Complete." << endl;
system("pause");
}
You declare a 3x3x3 array.
Then you proceed to initialize as if it was a 4x4x4 array. Here's a simplified explanation of where your code goes wrong:
int foo[3];
This declares a 3-element array. foo[0] through foo[2].
for (int bar=0; bar<4; ++bar)
{
foo[bar]=1;
}
This attempts to initialize foo[0] through foo[3]. Four elements. Three-element array.
Undefined behavior.
Your code makes the same error, but with a 3-dimensional array, in all three dimensions.
fun[arrayRow][arrayColumns][arrayDepth]
allocates an array that can be indexed with a range of 0 .. 2 on each axis.
for (int r = 0; r < 4; r++){
roams from 0 to 3 and overruns the array.
for (int r = 0; r < arrayRow; r++){
will solve that. You will have to do the same for the other for loops as well as they are all out of range.
In addition,
cout << fun[arrayRow][arrayColumns][arrayDepth];
resolves to
cout << fun[3][3][3];
and is out of range and always returns the same value.
I have Array A[9]= {1,2,3,4,5,6,7,8,9} and I need to delete the numbers which are not dividing by 2. The code I tried to do:
int main()
{
int n;
ifstream fd(Cdf);
fd>>n; // read how many numbers are in the file.
int A[n];
for(int i = 0; i < n; i++)
{
fd >> A[i]; //read the numbers from file
}
for(int i = 0; i < n; i ++) // moving the numbers.
{
if(A[i] % 2 !=0)
{
for(int j = i; j < n; j++)
{
A[i] = A[i+1];
}
}
}
fd.close();
return 0;
}
But I get numbers like 224466888. what I need to do to get 2,4,6,8?
I need to delete numbers in the same array.
First you should use std::vector for dynamic size arrays.
Second, for removing numbers that are even in a vector, you can do :
std::vector<int> inf = {12,0,5,6,8};
auto func = [](int i){return i % 2 != 0;};
inf.erase(std::remove_if(inf.begin(),inf.end(),func), inf.end());
EDIT :
Ok, so you can still do this without std::vectors, but it will be uglier :
#include <algorithm>
int res[] = {2,5,9,8,6,7};
int size = 6;
auto func = [](int i){return i % 2 != 0;};
int new_size = std::remove_if(res,res + size, func) - res;
All the data you want is in [0, new_size[ range, the other part of your array is now garbage.
Your removal loop is indexing with the wrong variable:
for(int j = i; j < n; j++)
{
A[i] = A[i+1];
}
You're using i, which doesn't change in the loop.
Change it to j. You also need to subtract one from the upper limit, as you'd step outside of the array otherwise when accessing A[j + 1].
for(int j = i; j < n - 1; j++)
{
A[j] = A[j + 1];
}
An array can't be used for your purpose. It is allocated on stack and its size can't be changed dynamically (you can't change the size of an array in general, not only when it is allocated on stack).
You could allocate a second array and keep reallocating it with realloc everytime you add a new element but that's not the good way to do it. You are working with C++ so just use a std::vector<int> and your problems will be solved:
std::vector<int> evenArray;
evenArray.reserve(sizeof(A)/sizeof(A[0])/2);
if (number is even) {
evenArray.pushBack(number);
}
Mind that vector stores elements contiguously so this is legal:
int *evenA = &evenArray[0];
For your inner for loop you should be referencing j, not i.
for(int j = i; j < n - 1; j++)
{
A[j] = A[j+1];
}
Otherwise, what's the point of creating j?
Of course, this also means if you read the whole array back you will display all the characters that were shifted (which will just be equal to the last number). So, you should probably keep track of the new length of the array and just iterate to that instead of the end of the array.
EDIT:
In the inner for loop you need to loop to n - 1 otherwise when you have A[j + 1] it will go off the end of the array when you to change it, which may or may not give you a runtime error.