Hi, in gcc 4.1, the following sample throws a warning: /* gcc-4.1 -c test.c -Wall -Wconversion */ #include <stdbool.h> static int a(bool b) { return b ? 1 : 0; } int main(void) { return a(true); } test.c:10: warning: passing argument 1 of ‘a’ with different width due to prototype In gcc-4.3 however, that warning is gone. Where could I read more about this change?