OSDev.org

mac wrote:By your thinking, a good primer in C/C++ must be very elusive.

#include <stdio.h>

int main()
{
    int this_is_a_number;

    printf( "Please enter a number: " );
    scanf( "%d", &this_is_a_number );
    printf( "You entered %d", this_is_a_number );
    getchar();
    return 0;
}

• He uses scanf() to read user input, which is not a good idea to begin with. (Prefer fgets() and in-memory parsing of the whole input line using e.g. strtol(), which tells you exactly how far it parsed, handles too-large values gracefully, enables you to give the whole input line in error messages etc. etc.)
• He does not check the return code of scanf().
• This makes the following printf() undefined behaviour if you didn't input a number.
• printf() doesn't end the line with \n. (Mostly cosmetic, but still.)
• As the \n you entered after your number is not read and remains in the input buffer, the getchar() won't hold the execution as intended, the program exits immediately.

• They mentioned that C99 exists as a newer version of the standard, but not C11.
• They said "int f1() { ... }" is equivalent to "int f1(void) { ... }". The former however takes an unspecified number of arguments, while the latter takes no arguments.
• As an example, they defined an "int f2(void) { ... }" function and, probably to simplify things, they said that "printf(f2());" will print the return value of f2(). I wonder if there was anyone who tried to do that later and got a segfault.
• We are using scanf() for user input and we've never learned to check the return value.
• They showed us "for (int i = 0; i < 10; i++)", but the IDEs (DevC++ BTW) in lab's computers are in C89 mode.
  • Funny story, we had an assignment about a month later. I wrote it using C99/C11. The person who examined us (the one of the lab teachers) knew my code was correct, so she tried to hack it a bit, so it worked with C89. I told her "better compile the code as C99 or C11 instead" and she didn't know how do it. I did it for her by adding a simple gcc option.
• There have been other assignments too. One of them involved copying exactly the same code over all of the six switch cases we had to define. The current one involves using a multidimensional array of pointers that point to integers, strings and floats (of course excessive casting is unavoidable and I wonder if we will ever learn in the lab to use structs instead).