How Do I Fix This Loop? C ++ [duplicate] - c++

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Closed 10 years ago.
Possible Duplicate:
C++ Loop Not Looping Appropriately
Warning..I am new to C++ programming...I have an array of 20 x 20 that outputs how hot a plate is. I need to reiterate through a loop until no cell in the array changes more than 0.1 degree(I refresh the values through every iteration. How would you monitor the largest change for any cell in an array in order to determine when to stop iterating? Right now I have tried, but the below doesn't output correctly.
#include <iostream>
#include <string>
#include <fstream>
#include <iomanip>
using namespace std;
const int array_size = 20; // set array size and neighbors to calculate rest of cells
const int cell_neighbors = 4;
void initialize(double hot_plate[][array_size]); //functions here
bool writeFile(const double hot_plate[][array_size],
const string file_name);
double sum_cell(const double hot_plate[][array_size],
const int cell_X, const int cell_Y);
double value_cell(const double hot_plate[][array_size],
const int cell_X, const int cell_Y);
int main()
{
double hot_plate[array_size][array_size];//set variables
initialize(hot_plate); //run function
string file_name = "hot_plate.csv"; //file name for Excel
//repeat until stable
int repeat_until_stable = 1000;
while ( repeat_until_stable > 0)
{
for (int a = 1; a < array_size - 1; a++)
{
for (int b = 1; b < array_size - 1; b++)
{
{
hot_plate[a][b] = sum_cell(hot_plate, b, a);
}
}
}
repeat_until_stable--;
}
if (writeFile(hot_plate, file_name)) //check functionality of the program
{
cout << "Excel File created\n";
}
else
{
cout << "The Excel file did not write\n";
}
system("pause");
return 0;
}
//function definition
double sum_cell(const double hot_plate[][array_size],
const int cell_X, const int cell_Y)
{
double cell_num = hot_plate[cell_X - 1][cell_Y]; // Top
cell_num += hot_plate[cell_X][cell_Y - 1]; // Left
cell_num += hot_plate[cell_X][cell_Y + 1]; // Right
cell_num += hot_plate[cell_X + 1][cell_Y]; // Bottom
cell_num /= cell_neighbors; // find average of the 4 values closest to cell
return cell_num;
}
// setup the array so all values are defined
void initialize(double hot_plate[][array_size])
{
for (int a = 0; a < array_size; a++)
{
for (int b = 0; b < array_size; b++)
{
if (a == 0 || a == array_size - 1)
{
if (b == 0 || b == array_size - 1)
{
hot_plate[a][b] = 0.0;
}
else
{
hot_plate[a][b] = 100.0;
}
}
else
{
hot_plate[a][b] = 0.0;
}
}
}
}
double value_cell(const double hot_plate[][array_size],
const int cell_X, const int cell_Y)
{
double cell_value = hot_plate[cell_X][cell_Y]; // cell value
return cell_value;
}
// Write the data to the Excel CSV file
bool writeFile(const double hot_plate[][array_size],
const string file_name)
{
// open the excel file
ofstream fout(file_name);
if (fout.fail())
return false;
for (int a = 0; a < array_size; a++)
{
for (int b = 0; b < array_size; b++)
{
fout << hot_plate[a][b];
if ( b < array_size - 1)
{
fout << ", ";
}
else if (a != array_size - 1)
{
fout << endl;
}
}
}
// close the input stream from the file.
fout.close();
return true;
}

Answer 1

Put a variable that holds the maximum change that is made and check it after the for loops
double maxChange=.11;
.
.
.
while(maxChange>.1)
{
maxChange=-1;
for(.....)
for(.....)
{
change=fabs(oldValue-plate[a][b]);
if(change>maxChange)
maxChange=change;
}
}