int changeNum(int *n) {
++*n;
return*n;
}

int main(int argc, char **argv) {
int n = 0;
printf("%d %d %d\n", changeNum(&n), changeNum(&n), changeNum(&n));
system("pause");
return 0;
}
↑No undefined behavior here. The evaluation order of arguements is unspecified behavior, not undefined. And there is a sequence point before each function calling, so no object is modified more than once between two sequence points.
Undefined behavior shall be always wrong, while unspecified behavior can be right.