Why the output in the function is "7 18 5"

Question

#include <iostream>
using namespace std;
f1(Int &b,int c)
{b++;
return b+c;}

Int main()
{Int a=5;
cout<<a<<" "<<f1(a,f1(a,a)<<" "<<a;
return 0; }

Answer 1

First of all, a = 5 going to push into the stack.
The inner function call first happens f(5, 5) which makes a = 6
then the outer function call from the previous result which was 6 + 5 = 11 happens and f(6, 11) is going to execute.
Finally, after returning to main function, a = 7 and 7 + 11 = 18

now cout object take a look at the last stack value of 'a' variable returned by f function which is 7 then it evaluate the sequence of outputs.
for example if you had

count << a << " " << a << " " << a << " " << f(a, f(a,a)) << " " << a;

All 'a' variables became 7, then latest function return value , that is,18, and after the nested function call, last stack's value pops and you just get the initial value of a, which was 5.

Answer 2

You are getting output 7 18 5, please go through following steps

cout<<a<<" "<<f(a,f(a,a))<<" "<<a;
will be evaluated as
from right to left

std::cout.operator<<(a).operator<<(f(a,f(a,a))).operator<<(a);

1. .operator<<(a) will returns 5
2. .operator<<(f(a,f(a,a)))
f(a,a)
f(5,5)
a++= 6 step i
6 + 5 = 11 return statement
f(a,f(a,a)) =>
f(6,11)
a++= 7 step i
7 + 11 = 18 return statement
returns 18
3. std::cout.operator<<(a) returns 7 (as it was incremented twice)

Answer 3

right most expression will evaluated first
for example
in expression c=a+b compiler will first evaluates
a+b, then assigns the sum to the variable c.

Answer 4

@ Nour

Compiler and language architectures are low level stuff and even though you know the language rules but sometimes their behaviour toward some sort of expressions makes you confuse.

I suggest you to split it into 3 expression and see the result.

cout << a << " ";
cout << f(a, f(a, a));
cout << " " << a;

http://stackoverflow.com/questions/7718508/order-of-evaluation-of-arguments-using-stdcout

Answer 5

I did not understand .. now the. compiler works from right to left or from left to right ????

Answer 6

Babak sheykhan ... I am sorry but I did not understand why it printed 5 though a=7