int m = 5, d = 12, y = 1975, val;
// May 12, 1975
Can someone please explain the function/purpose of the comma operator in the line of code below:
val = (d+=m<3?y--:y-2,23*m/9+d+4+y/4-y/100+y/400)%7;
The above line was written by Mike Keith to calculate the day of the week given the date (d = day, m = month, y = year). Where Sunday = 0, Monday = 1, Tuesday = 2, Wednesday = 3, Thursday = 4, Friday = 5, Saturday = 6. I understand that the y-- gets executed if d+=m<3 is true, else the y-2 is executed. What I don't understand is the purpose of the comma after y-2.
The comma operator separates expressions to be executed one after the other, just like ;. But with , they constitute one whole expression that evaluates to the value of the last sub-expression. For example
int i = 1;
int j = (++i, i*2);
printf("%i", j)
prints out 4.
It can for example be used in for expressions, where 3 expressions need to be in the header. For example
for(i = 0, j = 0; i < n; i++, j++)