c++11 - how does the below code output 3? (how does the below code read?) -

the specific part not understand how -a in if statement changes -3 3. can explain how -a changes a = -3 a = 3?

#include <iostream>  int main(){  signed = -3;  if (a < 0){ std::cout << -a << std::endl; } else { std::cout << << std::endl; }  system("pause"); return 0; } 

it's example of unary negative, when a=-3 (which less 0, code enters if block) -a -(-3) 3.