What this code mean?

Question

https://code.sololearn.com/cq6sX0G85X1P/?ref=app

Answer 1

the expression x?y:z returns y if x is true, and z if x is false.
(-a == 1) is false so we have
a +=4;
which is equivalent to
a=a+4

Answer 2

//initialize a to 3 and b to 4
int a =3, b=4;

//recalculate a as follow:
// if( a==-1 ){
// a=a-3
// }
// else {
// a = a+4
// }

a+=(-a==1?-3:4);

//Now a is 7
//Print a
cout<<a;

Answer 3

Thank you!