Understand comma operator

Question

int main()
{
    int a = (1,2,3);
    int b = (++a, ++a, ++a);
    int c= (b++, b++, b++);
    printf("%d %d %d", a,b,c);
}

I am beginner in programming. I am not getting how does this program shows me output of 6 9 8.

Answer 1

The , used in all the three declarations

int a = (1,2,3);
int b = (++a, ++a, ++a);
int c = (b++, b++, b++);  

are comma operator. It evaluates the first operand¹ and discard it, then evaluates the second operand and return its value. Therefore,

int a = ((1,2), 3);          // a is initialized with 3.
int b = ((++a, ++a), ++a);   // b is initialized with 4+1+1 = 6. 
                             // a is 6 by the end of the statement
int c = ((b++, b++), b++);   // c is initialized with 6+1+1 = 8
                             // b is 9 by the end of the statement.

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_{1 Order of evaluation is guaranteed from left to right in case of comma operator.}