nested looping C++ - c++

Question

i want to asking this problem.
this output is the expected output
*
*#
*#%
*#%*
*#%*#
*#%*#%
and this is my solution
#include <iostream>
using namespace std;
int main(){
int a,b,n;
cout << "Input the row";
cin >> n;
for (a = 1; a <= n; a++){
for(b = 1; b <= a; b++){
if (b == 1 || b == 1 + 3){
cout << "*";
}
if (b ==2 || b == 2 + 3){
cout << "#";
}
if (b ==3 || b == 3 + 3){
cout << "%";
}
}
cout << endl;
}
}
this solution is only work if the n = 6. what should i do if i want this work in every row when user input the row to the n
thank you in advance.

Answer 1

Here, I tried using the modulo "%" on your if's
#include <iostream>
using namespace std;
int main(){
int a,b,n;
cout << "Input the row";
cin >> n;
for (a = 1; a <= n; a++){
for(b = 1; b <= a; b++){
// After every first digits will cout #
if (b % 3 == 2){
cout << "#";
}
// The first after the third digit will cout *
if (b % 3 == 1){
cout << "*";
}
// The third digit after the second digit will cout %
if (b % 3 == 0){
cout << "%";
}
}
cout << endl;
}
}

Answer 2

To make your solution work for any value of n, you can use the modulo operator % to check whether a given value of b is the first, second, or third element of each row.
Here is one way you could modify your code to do this:
#include <iostream>
using namespace std;
int main() {
int a, b, n;
cout << "Input the row: ";
cin >> n;
for (a = 1; a <= n; a++) {
for (b = 1; b <= a; b++) {
// Use the modulo operator to check whether b is the first, second, or third element of each row
if (b % 3 == 1) {
cout << "*";
} else {
if (b % 3 == 2) {
cout << "#";
} else {
cout << "%";
}
}
}
cout << endl;
}
return 0;
}
With this change, the code will output the correct pattern for any value of n.

Answer 3

Just adding a nice optimisation (note: C++ loops naturally go up from 0 to not including n, i.e. for(int i = 0; i < n; ++i) – this is especially relevant if you are indexing arrays which have a first index of 0 and last of n - 1, while n already is invalid!).
While you do use b % 3 to decide which character and you indeed can use this by chaining if(){} else if(){} else{} (where a switch() { case: case: default: } actually would have been preferrable) you can have a much more compact version as follows (and even more efficient as it avoids conditional branching):
for(int b = 0; b < a; ++b)
{
std::cout << "*#%"[b % 3];
}
The C-string literal "*#%" actually represents an array of char with length four (including the terminating null character) – and you can index it just like any other array you have explicitly defined (like int n[SOME_LIMIT]; n[7] = 1210;)...