What is the reason for printing the second value prior to the first value in printf statement?

Question

The following code:

void main
{
    int b=10;
    int a=5;
    printf("%d",(b,a));
}

This gives an output 5 on execution. Can anyone explain the reason for it?

I expected an output 10 since that is the first value that matches "%d".

Answer 1

Read about the comma operator. Your (b,a) expression is evaluated to 5 (the value of a).

^{Also, take the good habit of ending your printf format control strings with a newline \n or else call sometimes fflush (which gets automatically called after main, using atexit techniques). Remember that <stdio.h> streams are buffered!}

Answer 2

In C, (b,a) means "calculate b, then calculate and return a". So, It's practically the same as just a in your case.