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Discussion on: Is "C Programming language" Still Worth Learning in 2021?

atulsnjena profile image
Surya Narayan Jena


int main() {
int i = 1;
printf("%d, %d", i++, i+1);
return 0;

Please explain to a newbie,how this printf is working.
I was expecting 1,3 (please tell me if I am wrong) but compiler gives out 1,2 .
How is this happening ??

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pentacular profile image

C programs are understood in terms of the CAM (C Abstract Machine).

The compiler's job is to build a program that produces the same output as the CAM would for a given program.

The CAM says that a variable can only be read, or read-to-modify, once between two sequence points.

There are no sequence points between the i++ and i+1, so this produces a read/write conflict, which means that the program has undefined behavior in the CAM, and so the compiler can do whatever it wants.

It could crash, or print out 23, 37 or -9, 12, and these would all be equally correct behaviors.