learn-c-the-hard-waych13.txt

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Chapter 13
Exercise 12: If, Else-If, Else

   Something common in every language is the if-statement, and C has one.
   Here's code that uses an if-statement to make sure you enter only 1 or
   2 arguments:
     __________________________________________________________________

   Source 33: ex12.c
   1  #include <stdio.h>
   2
   3  int main(int argc, char *argv[])
   4  {
   5      int i = 0;
   6
   7      if(argc == 1) {
   8          printf("You only have one argument. You suck.\n");
   9      } else if(argc > 1 && argc < 4) {
   10          printf("Here's your arguments:\n");
   11
   12          for(i = 0; i < argc; i++) {
   13              printf("%s ", argv[i]);
   14          }
   15          printf("\n");
   16      } else {
   17          printf("You have too many arguments. You suck.\n");
   18      }
   19
   20      return 0;
   21  }
     __________________________________________________________________

   The format for the if-statement is this:
         if(TEST) {
             CODE;
         } else if(TEST) {
             CODE;
         } else {
             CODE;
         }

   This is like most other languages except for some specific C
   differences:
    1. As mentioned before, the TEST parts are false if they evaluate to
       0, and true otherwise.
    2. You have to put parenthesis around the TEST elements, while some
       other languages let you skip that.
    3. You don't need the {} braces to enclose the code, but it is very
       bad form to not use them. The braces make it clear where one branch
       of code begins and ends. If you don't include it then obnoxious
       errors come up.

   Other than that, they work like others do. You don't need to have
   either else if or else parts.

13.1 What You Should See

   This one is pretty simple to run and try out:
     __________________________________________________________________

   Source 34: ex12 output
   1$ make ex12
   2cc -Wall -g    ex12.c   -o ex12
   3$ ./ex12
   4You only have one argument. You suck.
   5$ ./ex12 one
   6Here's your arguments:
   7./ex12 one
   8$ ./ex12 one two
   9Here's your arguments:
   10./ex12 one two
   11$ ./ex12 one two three
   12You have too many arguments. You suck.
   13$
     __________________________________________________________________

13.2 How To Break It

   This one isn't easy to break because it's so simple, but try messing up
   the tests in the if-statement.

    1. Remove the else at the end and it won't catch the edge case.
    2. Change the && to a || so you get an "or" instead of "and" test and
       see how that works.

13.3 Extra Credit

    1. You were briefly introduced to &&, which does an "and" comparison,
       so go research online the different "boolean operators".
    2. Write a few more test cases for this program to see what you can
       come up with.
    3. Go back to Exercises 10 and 11, and use if-statements to make the
       loops exit early. You'll need the break statement to do that. Go
       read about it.
    4. Is the first test really saying the right thing? To you the "first
       argument" isn't the same first argument a user entered. Fix it.

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Related Books

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