Why do programs in C compile even when the return statement is missing? [duplicate]

Answer 1

I haven't seen the why addressed well in any of the answers so far. In C, it's perfectly legal for a function with a non-void return type to end without a return statement/value, as long as the caller does not attempt to use the return value. For instance (slightly nontrivial example):

#include 
int foo(int want_result)
{
    puts("hello");
    if (want_result) return 42;
}

int main()
{
    foo(0);
    printf("%d\n", foo(1));
}

This example is somewhat contrived, but it could actually become meaningful if the return type is a huge structure that would take non-trivial time to return.