[SOLVED] I didn't understand how this code works. Maybe someone can help!

Question

int a = 0, b = 0;
while (a < 7, b < 17) {
a++;
b++;
}
printf("%d, %d\n", a, b);

Answer 1

while( a < 17, b < 17 )

Here we have 2 expressions to evaluate, as loop condition. The 2 expressions are chained by comma operator, which evaluates its operands from left to right. Comma operator evaluates both operands, but only the rightmost operand ( b < 17 ) will be counted for as the final evaluation result.

That is why <a> and <b> are both incremented until <b> value equals to 17.

http://www.c4learn.com/c-programming/c-comma-operator/

Answer 2

I found this Stackoverflow question and answer interesting

https://stackoverflow.com/questions/4072578/inside-a-while-loop-is-the-last-comma-separated-statement-guaranteed-to-run-las

Answer 3

The expression a<7 is having no effect, because 17 is greater than 7 so when the variables 'a' and 'b' inside while become 16 then 16<17 so a and b gets incremented to 17(both). Then they get printed.

if you will use while(a<7 || b<17)
output will be 17,17
and for while(a<7 && b<17)
output will be 7,7 because of &&

in your case complier will also give warning.

Answer 4

Thanks! Ipang

Answer 5

Thanks! HK Lite

Answer 6

What an interesting explanation! Thanks! Paul K Sadler