Why and how does GCC compile a function with a missing return statement?

Question

#include 

char toUpper(char);

int main(void)
{
    char ch, ch2;
    printf(\"lowercase input : \");
    ch = getchar();
    ch2 = toUpper(ch);
             


        

Answer 1

You should keep in mind that such code may crash depending on compiler. For example, clang generates ud2 instruction at the end of such function and your app will crash at run-time.