size.c in your editor and read it. Try to guess what it will print out. Compile the code and run it.
$ clang -Wall -std=c11 -o size size.c
Did it print what you expected?
size.c and add additional
printf lines to print the sizes of
size_t. Compile your program and run it.
size.c one more time. This time, print the size of
bool. Try to compile the code. Clang gives two errors, the second is nonsensical, but the first is instructive. Try to compile with
gcc instead of
clang. You’ll get a very similar error.
Look closely at the error messages, they tell you a lot. They start by giving the name of the file, the line of the error, and the column of the error:
size.c:line:column:. This is followed by the error message and then the line of code with a marker indicating the place the compiler thinks you’ve made an error.
(You can have Vim show you line numbers by adding
set number to your
~/.vimrc or by running
:set number while Vim is running. You can have Emacs display line numbers too.)
This particular error is because C calls its Boolean type
_Bool. This is terrible. Fortunately, there’s a better way.
Add the line
#include <stdbool.h> at the top of
size.c. This makes
bool an alias (technically a
_Bool and defines
true as 1 and
false as 0. Compile and run it.
(If you’d like, you can read
/usr/include/clang/6.0/include/stdbool.h to see how that happens, but note we haven’t actually talked about most of what’s in there. Nevertheless, it should be fairly easy to follow what’s going on.)
to make sure your code is consistently formatted.
Create a new file,
fib.c. Write a function
long long fib(int n) that computes and returns the nth Fibonacci number. (Feel free to use either recursion or a loop. Make sure that any temporary variables you use have type
Below it, create a main function that calls
fib with the argument of your choice and prints out the result, e.g.,
int n = 19;
printf("F_%d = %lld\n", n, fib(n));
Format your code with
clang-format, compile and run it. Make sure you get the right answer!
Read the man page for
atoi. This function takes a string and returns an integer. Modify
fib.c to iterate over all of the command line parameters (excluding
argv which is the name of the program itself), call
atoi(argv[idx]) for each 1 ≤
argc, and print out the result.
Pay attention to which header file you need to include in order to use
atoi and make sure to
Format, compile, and test.
$ ./fib 0 19 12
F_0 = 0
F_19 = 4181
F_12 = 144
fib.c such that if any of the arguments are negative, it prints out an error message rather than the value of the Fibonacci number. If any of the arguments are negative, make
main return 1 to indicate error.
Recall that error messages should go to
stderr rather than
stdout. We can use
fprintf to print to the
fprintf(stderr, "%s: Error: negative number: %s\n", argv, argv[idx]);
$ ./fib 2 -3 6
F_2 = 1
./fib: Error: negative number: -3
F_6 = 8
$ echo $?