creating hollow square c++ [closed] - c++

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I have written this code but somehow when it asks the user to enter a new number to create a square, it doesn't print the square. Could anyone anyone explain / help me please?
// ask user to repeat the process again at end of the first promt
while ( num > 1 || num < 20 )
{
ask user to repeat the process again at end of the first promt
while ( num > 1 || num < 20 )
{
// ask user t enter a square
cout << "Please enter size of square between #1-20: \n";
cin >> buf; num = atoi (buf.c_str());
cin.ignore(1000, 10);
// process of printing square
while ( num >= a)
{
b = 1;
while ( num >= b )
{
if ( a == 1 || a == num || b == 1 || b == num )
cout << "*";
else
cout << " ";
b++;
}
cout << endl;
a++;
}

Answer 1

I see no code where you initialise a to 1 so it may be it has some arbitrary value. If that arbitrary value is greater than num, the outer loop will never start.
For what it's worth, I would be using for loops in this case since you know in advance what the limits are, something like the following pseudo-code:
# Top line
for i = 1 to num (inclusive):
output "*"
output newline
# Middle lines
for i = 2 to num-1:
output "*" # Left char
for j = 2 to num-1: # Middle chars
output " "
output "*" and newline # Right char
# Bottom line
for i = 1 to num (inclusive):
output "*"
output newline
Then you don't have to worry about condition checking within the loop body.
A good rule of thumb is to use for for a known-before-the-start count of iterations, while for a loop where you don't know in advance how often you'll iterate.
Another likely problem is your condition:
while ( num > 1 || num < 20 )
Regardless of the value of num, that is always true, since you're using logical-or ||. Think of the possibilities:
num <= 1 : false or true -> true
num == 2..19 : true or true -> true
num >= 20 : true or false -> true
If you want to continue looping while you have a value outside of the range 1..20, you should use:
while ( num < 1 || num > 20 )
and you then end up with the following:
num <  1     : true or false -> true
num == 1..20 : false or false -> false
num >  20    : false or true -> true
There are quite a few other potential problems with your code, to wit:
You appear to have the outer loop in there twice.
You don't appear to define b or num.
You don't appear to set num before the outer loop (which checks it).
I suspect you meant to close the while ( num > 1 || num < 20 ) loop immediately after the cin.ignore() call since it's meant to keep going until you get a value from 1 to 20 and then draw the square. As it stands, a square will be drawn even if you enter 99.

Answer 2

Probably not the best code - but it can be done in six lines. Here goes.
for (int y = o; y < height; ++ y) {
for (int x = 0; x < width; ++x) {
cout << (y == 0 || y == (height - 1) || x == 0 || x == (width - 1) ? '*' : ' ' );
}
cout << endl;
}