C++ program

#include <iostream>
using namespace std;

// definition of printGrid method to print the grid of "size" rows and "size" columns
void printGrid(int size)
{
// if the argument size is a negative number, print error message
if(size<=0)
cout << "The grid can only have a positive number of rows and columns." << endl;
// if the argument size is a positive number, print the grid
else
{
/* outer for loop is repeated size number of times to print the following pattern
size times
+--+--+--+
| | | | */
for(int i=1; i<= size; i++)
{
/* This inner for loop prints the pattern "+--" size number of times in one row */
for(int i=1; i<=size; i++)
cout << "+--" ;
/* end every row by printing a final + symbol and moves cursor to next line */
cout << "+" << endl;
/* This inner for loop prints the pattern "| " size number of times in next row */
for(int i=1; i<=size; i++)
cout << "| " ;
/* end that row by printing a final | symbol and moves cursor to next line */
cout << "|" << endl;
}
/** this for loop is to print the last line of the pattern */
for(int i=1; i<=size; i++)
cout << "+--" ;
cout << "+" << endl;
}
}

int main()
{
// call the printGrid method with 3 as the argument
cout << "printGrid(3)" << endl;
cout << "************" << endl << endl;
printGrid(3);
cout << endl;

// call the printGrid method with -4 as the argument
cout << "printGrid(-4)" << endl;
cout << "************" << endl << endl;
printGrid(-4);
}

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https://media.cheggcdn.com/media/49e/49e5eb8c-0d12-4531-9f3a-5b0e8174a83b/phpkTImlW.png

https://media.cheggcdn.com/media/66e/66e126c3-7b90-4b40-97ae-632a60004d36/phpW9WzBZ.png
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Sample output
https://media.cheggcdn.com/media/2c5/2c532078-533a-497c-aba7-e7bbc9e73d2e/phpE27qgT.png