ch1-Hello

Chapter_1                                                            ch1-Temperature_Programs 

Contents:

hello.c     Exercise_1-1     Exercise_1-2     quotes.c

hello.c     K&R, p.6     (compile and run a program in C)     download 

#include <stdio.h> // no semicolon after directive

int main()

{

  printf("Hello, world!\n"); // 2 spaces indentation

  // normal return value for main():

  // return 0; // 0 signals no errors

}

/*

gcc -E hello.c // preprocessing

gcc hello.c // compiling

./a.out // running the program

a.out // running the program

Hello, world! // output

gcc hello.c -o hello // specify name of executable

./hello // run program

hello // run program

Hello, world!

*/

Notes:  When running programs, do not write the comments in the terminal window, for instance, write

gcc hello.c

./a.out

"." is the current directory. Both

program

and

./program

run the program "program" from the current directory.

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Exercise 1-1     K&R, p. 8     (Hello - error messages)

Exercise 1-1. Run the "hello, world" program on your system. Experiment with leaving out parts of the program, to see what error messages you get.

Contents:

hello1.c     hello2.c     hello3.c     hello4.c     hello5.c     hello6.c     hello7.c     hello8.c     hello9.c     hello10.c     hello11.c 

Semicolon after #include directive

hello1.c          download

#include <stdio.h>; // no semicolon after directive

int main()

{

  printf("Hello, world!\n"); 

}

/*

gcc hello1.c // Compiler gives a warning, but creates the executable:

hello1.c:1:19: warning: extra tokens at end of #include directive

    1 | #include <stdio.h>; // no semicolon after directive

      |                   ^

./a.out

Hello, world!

*/

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Missing (commented out)  #include <stdio.h>

hello2.c          download

//#include <stdio.h>

int main()

{

  printf("Hello, world!\n");

}

/*

gcc hello2.c // compile

// Error message:

hello2.c: In function ‘main’:

hello2.c:5:3: warning: implicit declaration of function ‘printf’ 

[-Wimplicit-function-declaration] // line 5, column 3

    5 |   printf("Hello, world!\n");

      |   ^~~~~~

hello2.c:5:3: warning: incompatible implicit declaration of built-in function ‘printf’

hello2.c:1:1: note: include ‘<stdio.h>’ or provide a declaration of ‘printf’

  +++ |+#include <stdio.h>

    1 | //#include <stdio.h>

*/

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Missing ending '>' after 'stdio.h'

hello3.c          download

#include <stdio.h

int main()

{

  printf("Hello, world!\n");

}

/*

gcc hello3.c

hello3.c:1:18: error: missing terminating > character

    1 | #include <stdio.h

      |                  ^

*/

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Missing '#' before 'include'

hello4.c          download

include <stdio.h>

int main()

{

  printf("Hello, world!\n");

}

/*

gcc hello4.c

hello4.c:1:9: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘<’ token

    1 | include <stdio.h>

      |         ^

*/

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<stdio>  not recognized, write  <stdio.h>

hello5.c          download

#include <stdio>

int main()

{

  printf("Hello, world!\n");

}

/*

gcc hello5.c

hello5.c:1:10: fatal error: stdio: No such file or directory

    1 | #include <stdio>

      |          ^~~~~~~

compilation terminated.

*/

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Missing terminating  "  for  printf()  argument

hello6.c          download

#include <stdio.h>

int main()

{

  printf("Hello, world!\n);

}

/*

gcc hello6.c

hello6.c: In function ‘main’:

hello6.c:5:10: warning: missing terminating " character

    5 |   printf("Hello, world!\n);

      |          ^

hello6.c:5:10: error: missing terminating " character

    5 |   printf("Hello, world!\n);

      |          ^~~~~~~~~~~~~~~~~~

hello6.c:6:1: error: expected expression before ‘}’ token

    6 | }

      | ^

hello6.c:5:10: error: expected ‘;’ before ‘}’ token

    5 |   printf("Hello, world!\n);

      |          ^

      |          ;

    6 | }

      | ~         

*/

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Missing ending ')' for  printf()

hello7.c          download

#include <stdio.h>

int main()

{

  printf("Hello, world!\n"; 

}

/*

gcc hello7.c 

hello7.c: In function ‘main’:

hello7.c:5:27: error: expected ‘)’ before ‘;’ token

    5 |   printf("Hello, world!\n"; 

      |                           ^

      |                           )

hello7.c:5:28: error: expected ‘;’ before ‘}’ token

    5 |   printf("Hello, world!\n";

      |                            ^

      |                            ;

    6 | }

      | ~                           

*/

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Missing semicolon after  printf()

hello8.c          download

#include <stdio.h>

int main()

{

  printf("Hello, world!\n")

}

/*

gcc hello8.c

hello8.c: In function ‘main’:

hello8.c:5:28: error: expected ‘;’ before ‘}’ token

    5 |   printf("Hello, world!\n")

      |                            ^

      |                            ;

    6 | }

      | ~                           

*/

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Missing ending '}' for  main()

hello9.c          download

#include <stdio.h>

int main()

{

  printf("Hello, world!\n");

//}

/*

gcc hello9.c

hello9.c: In function ‘main’:

hello9.c:5:3: error: expected declaration or statement at end of input

    5 |   printf("Hello, world!\n");

      |   ^~~~~~

*/

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Missing   main()  function declaration

hello10.c          download

#include <stdio.h>

//int main()

{

  printf("Hello, world!\n");

}

/*

gcc hello10.c

hello10.c:4:1: error: expected identifier or ‘(’ before ‘{’ token

    4 | {

      | ^

*/

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Missing  main()  altogether

hello11.c          download

#include <stdio.h>

//int main()

//{

  printf("Hello, world!\n");

//}

/*

gcc hello11.c

hello11.c:5:10: error: expected declaration specifiers or ‘...’ before string constant

    5 |   printf("Hello, world!\n");

      |          ^~~~~~~~~~~~~~~~~

*/

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Exercise 1-2     K&R,  p. 8     (Print escapes)

Exercise 1-2.  Experiment to find out what happens when printf()'s argument string contains \c, where c is some character not listed above.

helloc.c          download

#include <stdio.h> // for printf()

int main()

{

  printf("Hello,\t\'world!\b\'\n");

}

/*

gcc helloc.c

./a.out

Hello,  'world'

*/

Notes: \t  is tab,  \b  is backspace,  \'  produces  ',  !\b  deletes  !

You could also include  \"  for quotes within the quoted string argument of  printf(), as in

printf("Hello, \"world!\"\n"); 

which produces the output

Hello, "world!"

You can also include  \f  (form feed),  \v  (vertical tab),  \r  (carriage return) or other escape_sequences.

See also quotes.c, Exercise_1-10, and Exercise_3-2. 

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quotes.c      (Equivalent forms)     download

#include <stdio.h> // for putchar(), printf()

// single and double quotes

int main()

{ // equivalent chars: '"' and '\"', and strings: "'" and "\'"

  printf("'\"':  "); putchar('"'); printf("\t  \"'\":  "); printf("'\n");

  printf("'\\\"': "); putchar('\"'); printf("\t  \"\\'\": "); printf("\'\n");

  return 0;

}

/*

gcc quotes.c -o quotes

./quotes

'"':   "   "'":  ' // quotes as a char, apostrophe in a string

'\"':  "   "\'": ' // escaped quotes as a char, escaped apostrophe in a string

*/

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