Can someone explain this code in JavaScript with ++ and brackets?

Question

var m=10;
n=(m++)+(++m)+(m++)+(++m);

Output is

n=48 m=14

How does this answer occur?

Answer 1

Initially m=10 . Now when ++ is executed, it will add 1 to the variable. In your code, there are 4 occurences of either ++m or m++ , so it will be 14 at the end.

When ++ appears before the variable like ++m , it will add 1 first and use the variable in code. But when it appears after the variable like m++ , the variable will be used first and then add 1.

So in n=(m++)+(++m)+(m++)+(++m); ,
m++ - m will be used in code as 10 and becomes 11.
++m - m will be incremented by 1 first, so 11+1 =12 and will be used in code.
m++ - m will be used in code as 12 and becomes 13.
++m - m will be incremented by 1 first, so 13+1 =14 and will be used in code.

So, final result will look like this: n=10+12+12+14

 var m = 10; var m1 = m++; var m2 = ++m; var m3 = m++; var m4 = ++m; var n = m1 + m2 + m3 + m4; console.log('n: ' + n); console.log('m: ' + m); console.log('(m++): ' + m1 + ', (++m): ' + m2 + ', (m++): ' + m3 + ', (++m): ' + m4); console.log('---'); var x = 10; var y = (x++) + (++x) + (x++) + (++x); console.log('y: ' + y); console.log('x: ' + x);

Answer 2

m++ this will use previous value of m then increment. ++m this will first increment and then use the incremented value of m.

now, n=(m++)+(++m)+(m++)+(++m) ;

-> m++ here the value of m will be first used then increased by 1. so expression will be 10 + (++m) + (m++) + (++m) . and for further value of m will be 11.

-> for next it is ++m so it will first increment then use in expression. so previously the value of m was 11, now 11+1 is 12. so expression will look like 10+12 + (m++) + (++m) .

-> similarly to first point here also it will first used then increment. so expression will be n=10+12+12+(++m) . but after this the value of m is now 13.

-> so here (++m) it will first increment and then add. so previously the value was 13 so 13+1=14. so m is 14 and expression will be n=10+12+12+14 .

so the value of n=48 and m=14