Some of the puzzling things about c language

Can you guess why there is no distinct format specifier for 'double' in the printf/scanf format string, although it is one of the four basic data types? (Remember we use %lf for printing the double value in printf/scanf; %d is for integers).

Ans: In older versions of C, there was no 'double'—it was just 'long float' type—and that is the reason why it has the format specifier '%lf' ('%d' was already in use to indicate signed decimal values). Later, double type was added to indicate that the floating point type might be of 'double precision' (IEEE format, 64-bit value). So a format specifier for long float and double was kept the same.

Why is the output file of the C compiler called a.out?

Ans: The a.out stands for 'assembler.output' file [2]. The original UNIX was written using an assembler for the PDP-7 machine. The output of the assembler was a fixed file name, which was a.out to indicate that it was the output file from the assembler. No assembly needs to be done in modern compilers; instead, linking and loading of object files is done. However, this tradition continues and the output of cc is by default a.out!

what is the use of volatile keyword in c?

The meaning of volatile is a popular interview question, particularly for freshers and I've read articles describing the properties of this keyword as if it had super powers.

The volatile keyword does a very simple job. When a variable is marked as volatile, the programmer is instructing the compiler not to cache this variable in a register but instead to read the value of the variable from memory each and every time the variable is used. That's it – simple isn't it?

To illustrate the use of the keyword, consider the following example:

volatile int* vp = SOME_REGISTER_ADDRESS;
for(int i=0; i<100; i++)
foo(*vp);
In this simple example, the pointer vp points to a volatile int. The value of this int is read from memory for each loop iteration. If volatile was not specified then it is likely that the compiler would generate optimized code which would read the value of the int once, temporarily store this in a register and then use the register copy during each iteration.

hope after reading this you reply confidently, when the same question is asked to you in the interview