Style is really not good nor bad, rather personal.
I've never seen anyone && two streams together in a condition, but have no trouble understanding what it means, and it does actually condense the code, so its not really a bad idea in that case. I would have written the code like this
Code:
#include <iostream>
using namespace std;
int main(void){
int n;
while(std::cout << "Enter the number of lines (e to quit): " && std::cin >> n){
for(int i = 0; i <= n; ++i){
// if no braces, put it on the same line
for(int k = 0; k < n - i; ++k) std::cout << " ";
// if using braces, put it on a different line
for(int m = 1; m < i * 2; ++m) {
std::cout << "*";
}
std::cout << endl;
}
} // no code after closing bracket
return EXIT_SUCCESS;
}