Why does the expression a = a + b - ( b = a ) give a sequence point warning in c++?

Question

Following is the test code:

int main()
{
    int a = 3;
    int b = 4;
    a = a + b - (b = a); 

    cout << \"a :\" << a << \" \" <<         


        

Answer 1

a = b + a - a; is just written as

a = b + a - (b = a)------>> (exp 1)

The following three results same as (exp 1) a = (b + a - (b = a)); a = ((b + a) - (b = a)); a = (b + a) - (b = a);

Observations +, - operators has got same precedence and also left to right associativity Hence 'b+a' gets executed first and then 'a' value gets assigned to 'b' before subtraction

Now observe the following When a = 10 and b = 20;

a = (b = a) - b + a; =======> a = 10; b = 10 a = ((b = a) - b + a); =======> a = 10; b = 10

a = ((b = a) - (b + a)); =======> a = -10; b = 10 From the above expressions its clear that even if innermost parenthesis gets executed first the associativity is followed first and then the precedence

Note: To avoid confusion between the precedence of outer and inner parenthesis Consider the following expression a = (b + a - (b = a)) =====> Actual Result => a = 20, b = 10; would have been a = 10, b = 10; (if precedence is primary when compared to associativity) Thus by the above example we can say that associativity is primary when compared to precedence