I don't understand the use of std:: setw
I'm doing an exercise from a C++ book that I use to learn the language, and I can't quite understand the use of std::setw and its joint use with std::left (by default) and std::right. In fact, I do not know how, I have come up with the key to perform what I wanted to do, but I do not understand why it works..
Tell me if I'm wrong, please, but according to what I think:
- the for J loop causes unfold the first triangle of *.
- the Line cout causes the b's to be separated from the * in each line to the right of each *, in 16-I spaces, starting from the character immediately to each *.
- the for z Loop adds the Triangle composed of letters b.
- the instruction cout is where I get lost, because I could not get that result that is the one I want, and do not tell me why, if it was intuition or that, but gave me to put the "* 2 " and so that came out xd
Please, I know it's a lot to ask, but if anyone could explain to me why it works and why I struggle so much with that instruction I would greatly appreciate it.
#include <iostream>
using std::cout;
using std::endl;
#include <iomanip>
using std::setw;
using std::right;
using std::left;
int main() {
for(int i = 1; i <= 10; i++) {
for(int j = i; j >=1; j--)
cout << '*';
cout << right << setw(16 - i);
for(int z = 11 - i; z >= 1; z--)
cout << 'b';
cout << right << setw(4 + i * 2);
for(int y = 11 - i; y >= 1; y--)
cout << 'a';
cout << endl;
}
return 0;
}
I also put the output that gives me, in case it was not portable.
* bbbbbbbbbb aaaaaaaaaa
** bbbbbbbbb aaaaaaaaa
*** bbbbbbbb aaaaaaaa
**** bbbbbbb aaaaaaa
***** bbbbbb aaaaaa
****** bbbbb aaaaa
******* bbbb aaaa
******** bbb aaa
********* bb aa
********** b a
2 answers
If I understood your question cout << right << setw(4 + i * 2); forms the pyramid of spaces in between because the space you increment to 4 by the sum of i is doubled, think that if you had this statement cout << right << setw(4 + i); Your result would be something like:
* bbbbbbbbbb aaaaaaaaaa
** bbbbbbbbb aaaaaaaaa
*** bbbbbbbb aaaaaaaa
**** bbbbbbb aaaaaaa
***** bbbbbb aaaaaa
****** bbbbb aaaaa
******* bbbb aaaa
******** bbb aaa
********* bb aa
********** b a
By multiplying i by 2 the space you leave for each line between b and a is doubled, when i = 1 will leave 6 spaces, in the next line will leave 8 and so progressively.
You have the loop i that serves to print the rows. For each row you will print a number of asterisks equal to the position of The Row (Row 1 -> 1 asterisk, Row 2 -> 2 asterisks, ...).
The next element to print is the sequence of b. As you want this new sequence to start in always in the same column you have to add after the sequence of asterisks a number of spaces such that número de asteriscos + número de espacios = x or, in other words, número de espacios = x - número de asteriscos, being in your case x=16. Since the sequence of asterisks is directly proportional to the row, the number of asterisks must be inversely proportional. From here you get the first setw: setw(16 - i);:
Fila i = i asteriscos + (16 - i) espacios
Fila 01: 1 asterisco + (16-1) espacios = 16
Fila 02: 2 asteriscos + (16-2) espacios = 16
Fila 03: 3 asteriscos + (16-3) espacios = 16
...
Well, now the sequence of b and the sequence of a are printed in such a way that the gap between them forms a pyramid of spaces, occupying the total sequence 24 characters. Both sequences, a and b, evolve inversely proportional to the row number. Thus we have:
24 = longitud_secuencia_b + espacios + longitud_secuencia_a
24 = (10-i) + espacios + (10-i)
24 = 2 * (10-i) + espacios
And now we try to calculate the number of spaces to insert based on the row number:
espacios = 24 - 2*(10 - i)
espacios = 24 - 20 + 2*i
espacios = 4 + 2*i
If you compare the latter result with the second setw you will see that the equation is exactly the same: setw(4 + i * 2);
Why that x2? Because the number of elements in the sequence a is reduced by one in each row and the same for the sequence b, accordingly, the number of spaces will have to grow by two units between a row and the next if you want the total sequence to occupy the same number of characters.