Why is my loop executed too often? - c++

I am designing a program for a C++ class that I am taking and the professor wants us to make a program that outputs a diamond shape using "*". The thing I am stuck on is that my program is outputting too many lines.
Instead of
*
***
*
It is outputting
*
***
*****
***
*
How would I modify my code to get this to work? I have been searching online for an answer all morning with no luck.
Here is my code:
#include <iostream>
using namespace std;
int main () {
//Define Varaible
int N;
cout << "Please enter a postitive integer: ";
cin >> N;
cout << "Here is your diamond." << endl << endl;
for (int i = 0; i <= 2 * N; i++) {
for (int j = 0; j <= 2 * N; j++) {
if (i <= N) {
if (j < N - i || j > N + i) {
cout << ' ';
}
else {
cout << '*';
}
}
else {
if (j < i - N || j > 3 * N - i) {
cout << ' ';
}
else {
cout << '*';
}
}
}
cout << endl;
}
return 0;
}

The reason you get more rows than you expect is that you are creating 2 * N + 1 number of rows, when you actually want 2 * N - 1.
The fix is simple: Decrement N by one after you read the input.
cin >> N;
assert(N > 0);
--N;
This way, the rest of your code won't have to change.

You should remember that in range [0,5] (both inclusive) there are 6 elements, not 5. So when you do loops and you want to do 5 iterations you usually do either:
for( int i = 0; i < 5; ++i ) // do stuff
or
for( int i = 1; i <= 5; ++i ) // do stuff
When programming in C or C++ first version is used more often as it fits array indexes and programmers have habit to use that form.
But as I said before if you do:
for( int i = 0; i <= 5; ++i ) // do stuff
That would be 6 iterations.

Related

Checking how many times a number has been entered

I'm trying to solve one of the questions on a task sheet I've received, to help me further in my understanding of C++ code from my class.
It kept showing 100000 in output after I entered the values. Where is that 1 coming from?
I know there are better ways to write code for this but I just want to know were is my problem.
The question is
(and I quote):
Write a program that:
Asks the user to enter 10 numbers between 1 and 5 into an array and displays the array on screen.
Creates a second array of size 5 and fills it with zeros.
Counts how many 1s, 2s, , … 5s have been entered into the first array and stores this number in the second array.
Displays the second array as shown in the example below.
Code:
int A1[10];
int A2[5] = { 0,0,0,0,0 };
int count = 10;
for (int i = 0; i < count; i++)
{
here:
cout << endl << i + 1 << "- enter a number between 1 and 5 for value : ";
cin >> A1[i];
if (A1[i] < 1 || A1[i]>5)
{
cout << "eror! enter a number between 1 and 5!";
goto here;
}
}
for (int i = 0; i < 10; i++)
{
for (int j = 1; j < 6; j++)
{
if (A1[i] = j)
{
A2[j - 1]++;
break;
}
}
}
for (int i = 0; i < 5; i++)
cout << A2[i];
The error is on the row 21 or 22, you are using a single = which is the assignment sign, inside the if statement, so you are overwriting the value of A[i] to the value of j, but want to check if the element of A[i] is equal to j... So you have to add a = in the if statement.
I don't recommend that you use goto:, it creates spaghetti code. you can put an i-- in your error clause, like so:
int temp;
for (int i = 0; i < count; i++){
cout << i + 1 << "- enter a number between 1 and 5 for value : " << endl;
cin >> temp;
if (temp >= 1 && temp <=5)
A1[i] = temp;
else
i--;
}
Also, if you want to compare 2 values, you should use the == operator. that is what's causing the problem in your second loop
like so:
for(int i = 0; i < count; i++){
for(int j = 1; j < 6; j++)
if(A1[i] == j)
A2[j-1]++;
}
This should work.

How to print diamond shape w/ c++

I need help, I created a short little program a while ago where it would print a simple pyramid with "*" like this:
*
***
*****
but I decided to challenge myself and see if I could create a simple diamond shape like this:
*
***
*****
***
*
Here is my code so far.
I should also add that the value you input, for example 5, determines how big the diamond is.
#include <iostream>
#include <sstream>
using namespace std;
int main() {
int value = 0;
cout << "Please enter in a value: ";
cin >> value;
cout << endl;
for (int i = 0; i < value; i++) {
//print spaces v v v
for (int x = 0; x < (value - i - 1); x++) {
cout << " ";
}
//print * v v v
for (int y = 0; y < (2 * i + 1); y++) {
cout << "*";
}
cout << endl;
}
for (int i = 0; i < value; i++) {
int number = 0;
number+= 2;
//print spaces v v v
for (int x = 0; x < (value - value + i + 1); x++) {
cout << " ";
}
//print * v v v
for (int y = 0; y < (/*ATTENTION: What do I do here? Plz help*/); y++) {
cout << "*";
}
cout << endl;
}
return 0;
}
What I've been trying to do is figure out what to put inside the parenthesis where it says (//ATTENTION). I've been working for at least an hour trying to do random things, and one time it worked when I input 4, but not for 5, and it's just been very hard. This is key to building the diamond, try putting in just value and compile to see what happens. I need it to be symmetrical.
I need to know what to put inside the parenthesis please. I'm sorry this is very long but the help would be appreciated thanks.
I also apologize if my code is messy and hard to read.
int number = 0; and number+= 2;
value - value inside for (int x = 0; x < (value - value + i + 1); x++) {
are not required.
Inside the parenthesis, you can use
2*(value-i-1)-1
However, I would suggest you to first analyze the problem and then try to solve it instead of trying random things. For instance, let's consider the cases of even and odd inputs i.e., 2 and 3.
Even Case (2)
*
***
***
*
The Analysis
Row Index Number of Spaces Number of Stars
0 1 1
1 0 3
2 0 3
3 1 1
For row index < value
Number of Spaces = value - row index - 1
Number of Stars = 2 * row index + 1
For row index >=value
The number of spaces and stars are simply reversed. In the odd cases, the situation is similar too with a small exception.
Odd Case (3)
*
***
*****
***
*
The Analysis
Row Index Number of Spaces Number of Stars
0 2 1
1 1 3
2 0 5
3 1 3
4 2 1
The small exception is that while reversing, we have to ignore the row index = value.
Now, if we put the above analysis in code we get the solution
//Define the Print Function
void PrintDiamond(int rowIndex, int value)
{
//print spaces v v v
for (int x = 0; x < value - rowIndex -1; x++) {
cout << " ";
}
//print * v v v
for (int y = 0; y < 2 * rowIndex + 1; y++) {
cout << "*";
}
cout << endl;
}
And then inside main
//Row index < value
for (int i = 0; i < value; i++) {
PrintDiamond(i,value);
}
//For row index >= value reversing the above case
//value-(value%2)-1 subtracts 1 for even and 2 for odd cases
//ignore the row index = value in odd cases
for (int i = value-(value%2)-1; i >=0; i--) {
PrintDiamond(i,value);
}
#include <iostream>
#include <sstream>
using namespace std;
int main() {
int value = 0;
cout << "Please enter in a value: ";
cin >> value;
cout << endl;
for (int i = 0; i < value; i++) {
//print spaces v v v
for (int x = 0; x < (value - i - 1); x++) {
cout << " ";
}
//print * v v v
for (int y = 0; y < (2 * i + 1); y++) {
cout << "*";
}
cout << endl;
}
for (int i = 0; i < value-1; i++) {
// int number = 0;
// number+= 2;
// //print spaces v v v
for (int x = 0; x < i+1; x++) {
cout << " ";
}
//print * v v v
for (int y = 0; y < (2*(value-1-i)-1); y++) {
cout << "*";
}
cout << endl;
}
return 0;
}
I hope that you will get this .Also in the second for loop you were iterating it one extra time by iterating the loop upto value. But since the pyramid is symmetric so the no of rows in the pyramid will be 2*value-1.So I in the second loop i should vary upto value -1.
This code should resolve the problem:
#include <sstream>
using namespace std;
void printSpaces(int howMany) {
for(int i = 0; i < howMany; i++) cout << " ";
}
void figure(int size) {
bool oddSize = size % 2 == 1;
int center = size / 2;
int spaces = size / 2;
// If figure is of an odd size adjust center
if (oddSize) {
center++;
} else { // Else if figure is of even size adjust spaces
spaces--;
}
for (int i = 1; i <= center; i++) {
printSpaces(spaces);
for(int j = 0; j < 1 + (i - 1) * 2; j++) cout << "*";
cout << endl;
spaces--;
}
spaces = oddSize ? 1 : 0; // If the figure's size is odd number adjust spaces to 1
center -= oddSize ? 1 : 0; // Adjust center if it's an odd size figure
for(int i = center; i >= 1; i--) {
printSpaces(spaces);
for(int j = 0; j < 1 + (i - 1) * 2; j++)
cout << "*";
cout << endl;
spaces++;
}
}
int main() {
int value = 0;
while(value < 3) {
cout << "Please enter in a value (>= 3): ";
cin >> value;
cout << endl;
}
figure(value);
return 0;
}

Program crashes when I try to input values

so I've got integers m and n in my program, once you input the values it should create an array with values from m to n (for example m = 1 and n = 10, it creates array q with values from 1 to 10). Then it looks in the array if there are any numbers that are equal to any two number summ that are squared (for example, in the array, number 5 is equal to 1 squared + 2 squared). The problem is when I try to input the first value it crashes, pretty sure the problem is in the function but can't seem to figure it out. Thanks
#include <iostream>
using namespace std;
int squared (int a, int b, int q[]){
while (a<=0 || b<=0){
cout <<"You can't input an integer that is 0 or below: ";
cin >>a;
cin >>b;
if (a>0 || b>0) break;
}
for (int p=0; p<b; p++){
for (int i=a ; i<b; i++){
q[p] = a;
}
}
for (int z=0; z<b; z++){
for (int x=0; x<b; x++){
for (int c=0; c<b; c++){
if (q[z] == (q[x] * q[x]) + (q[c] * q[c])){
int result= (q[x] * q[x]) + (q[c] * q[c]);
return result;
}
}
}
}
}
int main () {
int m,n;
int M[100];
cout <<"Input integers m un n: ";
cin >>m,n;
cout <<squared(m,n,M);
return 0;
}
Most likely it crashes because of this: cin >>m,n;, it should be cin >> m >> n;, else you use n uninitialized on the next line, thus getting undefined behaviour, e.g. crash.
What compiler are you using and with what flags, since this would trigger some warnings/errors at compile normally.
cin >> m, n; is incorrect which inputs only m which can be interpreted as:
(cin >> m), n; which means: cin, n; to correct it:
cin >> m >> n;
if(a > 0 || b > 0) break; is redundant because you check for this condition twice: once in while condition second inside while loop thus checking for the same condition is redundant because while breaks automatically if the condition succeeds (a or b is equal or smaller than 0).
you passed an array without passing its size, you are lucky if you set the first element 1 the any second value is equal to the size of array eg:
m = 1; n = 10; then the size is ten which is correct.
what about:
m = 7; n = 10; // now is size 10? it's only 3
to correct it pass the size eg:
m = 4; n = 8;
int size = 8 - 4;
cout << Squared(m, n, M, size);
also:
for (int p = 0; p < b; p++)
{
for (int i = a ; i < b; i++)
{
q[p] = a;
}
}
you are assigning the same value a to all elements of array and iterating doing the same thing in the nested-loop!!! it's likely to write:
int x = 0; x = 0;
so the condition of result inside squared will never succeed because the same value is never equal to its square. 4 = 4 * 4 is never reached
here is what you search for:
#include <iostream>
using namespace std;
// I only make squared search for the result not inputing m and n lik e in yours
int squared (int m, int n, int* M)
{
int result;
for(int i(0); i < n; i++)
for(int j(0); j < n; j++)
for(int k(0); k < n; k++)
if( (M[i] == ( (M[j] * M[j]) + (M[k] * M[k]) )) && j != k) // here to avoid comparing with the same index
{
cout << M[i] << " = (" << M[j] << "*" << M[j] << ") + (" << M[k] << "*" << M[k] << ")" << endl;
result = ( (M[j] * M[j]) + (M[k] * M[k]) );
cout << result << endl;
return result; // if success we return result
}
return -1; // otherwise we return -1 as a sign of error (no square yields in negative value)
}
int main ()
{
int n, m, size;
do
{
cout <<"m: ";
cin >> m;
cout << "n: ";
cin >> n;
if(n <= 0 || m <= 0)
cout <<"You can't input an integer that is 0 or below: ";
// also it's very important to check whether n is greater than m or not because if m == n or m > n then size will be negative and as you know no array has a negative nor 0 size
if(m >= n)
cout << "n must be greater than m!" << endl;
}while (m <= 0 || n <= 0 || m >= n);
size = n - m; // getting size of array assuming m can be any value
int* M = new int[n - m]; // allocating dynamic array
// inputting array as you asked
for(int i(0), j = m; i < size; i++, j++)
M[i] = j;
// checking the values of array elements
for(int i = 0; i < size; i++)
cout << M[i] << ", " ;
cout << endl;
// getting the result
cout << squared(m, n, M) << endl;
// cleaning
delete[] M;
return 0;
}

No output from cout when calling void function

I'm new to C++ so bear with me.
I am trying to create a histogram from certain parameters (interval size, length of array containing quantities of numbers, highest number yadayada).
The details are irrelevant and a problem for myself to fiddle with, although I think I got the correct formula in my function.
When I assign variables from the C++ IO "cin" I can output those with the "cout" call, however, when I call my histogram function, also containing "cout" instructions, nothing gets printed.
My code:
#include <iostream>
#include <cmath>
using namespace std;
void histogram(int l, int n, int k, int *a)
{
int quantity = 0;
for (int i = 1; i <= l; i++)
{
for (int j = 0; i < n; j++)
{
if (a[j] >= (i-1) * k || a[j] <= i * k)
{
quantity++;
}
}
cout << (i-1) * k + ": " + quantity << endl;
quantity = 0;
}
}
int main()
{
int l,n,k;
int *a;
a = new int[n];
cin >> l >> n;
for (int i = 0; i < n; i++)
{
cin >> a[i];
}
k = ceil((double)a[0]/l);
// cout << k;
histogram(l,n,k,a);
return 0;
}
There might be something funky going on with this line and string concatenation:
cout << (i-1) * k + ": " + quantity << endl; You might try rewriting as cout << ((i-1) * k) << ": " << quantity << endl; just to ensure that things are adding and concatenating correctly.

C++ unexpected memory error

I've problem with easy C++ program which finds the largest submatrix in given matrix:
int *A = new int[n*m];
... setting fields for matrix, finding the largest one and etc
... r := size of square-submatrix, max_i := row, max_j := column of the largest
for (i = max_i; i < max_i + r; i++)
{
for (j = max_j; j < max_j + r; j++)
cout << A[i * n + j] << "\t";
cout << "\n";
}
<memory free>
end of program
Everything works great (so it's not problem with logic) - finding correct submatrix, prinitng etc.
Unexpectedly (or due to late night) when I put in memory free line delete[] A or delete everything crushes down with errors (but it's still printing result correctly - so the error must be in this line). I've tried set it to NULL and every combination. What goes wrong?
Thanks in advance
EDIT:
#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
int i,j,k;
int m,n;
int r;
cout << "Size of matrix: \nRows: ";
cin >> n;
cout << "Columns: ";
cin >> m;
int *A = new int[n*m];
for (i = 0; i < n; i++)
{
for (j = 0; j < m; j++)
{
A[n*i + j] = rand() % 19 - 9;
cout << A[n*i + j] << "\t";
}
cout << "\n";
}
cout << "Size of submatrix: ";
cin >> r;
int liczba_kwadratow = (m + 1 -r) * (n+1 -r);
int max = -10000;
int max_i = 0;
int max_j = 0;
int row_iter = 0;
int col_iter = 0;
for (k = 0; k <liczba_kwadratow; k++)
{
int sum = 0;
for ( i = row_iter; i < row_iter + r; i++)
for ( j = col_iter; j < col_iter + r; j++)
sum += A[i * n + j];
if ( sum > max )
{
max = sum;
max_i = row_iter;
max_j = col_iter;
}
col_iter++;
if ( row_iter + r > m )
{
row_iter++;
col_iter = 0;
}
}
cout << "Field of the largest submatrix " << r << " of " << r << " equals " << max << "\n";
for (i = max_i; i < max_i + r; i++)
{
for (j = max_j; j < max_j + r; j++)
cout << A[i * n + j] << "\t";
cout << "\n";
}
...works great without delete[] A or delete A
}
The problem can at least be identified via the method(s) I've told you in the comments (or by using a debugger). Easiest way is changing the dynamical array to a std::vector then use member function at. You will then realize you get an out of bound exception thrown here:
for (i = 0; i < n; i++)
{
for (j = 0; j < m; j++)
{
A.at(n*i + j) = rand() % 19 - 9; // throws here!!!!, replace n by m
cout << A.at(n*i + j) << "\t";
}
cout << "\n";
}
When input is 6 5 3, then you get an exception when you first try to access A[30], which gives you a headache when delete[] - ing. Now you can figure out what's wrong I guess ...
You inverted i and j in your matrix access code.
basically the formula could be
current row + current column * number of rows
or
current row * number of columns + current column
Two remarks on your code and debugging:
using one-letter variables minimizes the wear and tear on your keyboard and fingers and reduces disk and memory usage. It tends to increase debugging time dramatically, though.
The assumption that the code is OK just because it does not crash immediately is absolutely wrong. C/C++ is the realm of undefined behaviours (in your case, probably the most common one: writing outside allocated memory). An UB is a nasty piece of work precisely because it can produce any outcome, including (frequently) an apparent absence of consequences, only to cause a perfectly OK bit of code to crash 10.000 lines later.