| Main |< C main() and printf() functions 1 | C/C++ Variable, Operator & Type 1 >| Site Index | Download |

---

 

 

 

 

 

 

 

C LAB WORKSHEET 4_1

C main() and printf() functions 2

 

 

 

 

 

 

 

 

Items in this page:

 

1. printf() function, it family and the standard output.

2. Tutorial references are: C/C++ intro & brief history, C/C++ data type 1, C/C++ data type 2, C/C++ data type 3 and C/C++ statement, expression & operator 1, C/C++ statement, expression & operator 2 and C/C++ statement, expression & operator 2. More printf() and its family examples can be found in C formatted input/output. A complete story of main() is in C and C++ main() story.

 

 

 

 

 

 

 

The _set_printf_count_output()

 

This function enable or disable support of the %n format in printf(), _printf_l(), wprintf(), _wprintf_l() family functions.

 

 

Program Example: // _set_printf_count_output() and _get_printf_count_output() example #include <stdio.h>   int main() {    int set, set2;    int i;    set = _set_printf_count_output(1);    printf("\'set\' value = %d\n", set);    printf("So, %%n support was %sabled.\n", set ? "en" : "dis");    // _get_printf_count_output() returns non-zero if %n is supported,    // 0 if %n is not supported.    set2 = _get_printf_count_output();    printf("\'set2\' value = %d\n", set);    printf("%%n support is now %sabled.\n", set2 ? "en" : "dis");    // %n format should set i to 7    printf("1234567%n890\n", &i);    printf("i = %d\n", i);    return 0; }   The Width Specification   The second optional field of the format specification is the width specification. The width argument is a nonnegative decimal integer controlling the minimum number of characters printed. If the number of characters in the output value is less than the specified width, blanks are added to the left or the right of the values - depending on whether the - flag (for left alignment) is specified - until the minimum width is reached. If width is prefixed with 0, zeros are added until the minimum width is reached (not useful for left-aligned numbers). The width specification never causes a value to be truncated. If the number of characters in the output value is greater than the specified width, or if width is not given, all characters of the value are printed. If the width specification is an asterisk (*), an int argument from the argument list supplies the value. The width argument must precede the value being formatted in the argument list. A nonexistent or small field width does not cause the truncation of a field; if the result of a conversion is wider than the field width, the field expands to contain the conversion result.

 

The Precision Specification

 

The third optional field of the format specification is the precision specification. It specifies a nonnegative decimal integer, preceded by a period (.), which specifies the number of characters to be printed, the number of decimal places, or the number of significant digits. Unlike the width specification, the precision specification can cause either truncation of the output value or rounding of a floating-point value. If precision is specified as 0 and the value to be converted is 0, the result is no characters output, as shown below:

 

printf("%.0d", 0);  /* No characters output */

 

If the precision specification is an asterisk (*), an int argument from the argument list supplies the value. The precision argument must precede the value being formatted in the argument list. The type determines the interpretation of precision and the default when precision is omitted, as shown in the following table.

 

How Precision Values Affect Type

 

The following Table lists types and precisions.

 

 

If the argument corresponding to a floating-point specifier is infinite, indefinite, or NAN (Not A Number - .Net framework), printf() gives the following output.

 

 

Program Example:

// using the printf() and wprintf() functions to produce formatted output example.

#include <stdio.h>

 

int main(void)

{

   char     chs = 'h', *string = "just a string";

   wchar_t  wch = L'w', *wstring = L"Unicode or multibyte";

   int      count = -8432;

   double   fpnt = 321.8842;

   // display integers

   printf("--Integer formats--\n Decimal: %d  Justified: %.6d  "

           "Unsigned: %u\n", count, count, count, count);

   // display decimals

   printf( "--Decimal %d as--\n HEX: %Xh  C hex: 0x%x  Octal: %o\n", count, count, count, count);

   // display in different radixes

   printf( "--Digits 10 equal--\n   Hex: %i  Octal: %i  Decimal: %i\n", 0x10, 010, 10);

   // display characters

   printf("--Characters in field #1--\n"%7c%3hc%3C%3lc\n", chs, chs, wch, wch);

   wprintf(L"--Characters in field #2--\n"

           L"%7C%5hc%5c%5lc\n", chs, chs, wch, wch);

   // display strings

   printf("--Strings in field #1--\n%10s\n"

          "%10.4hs\n   %S%10.3ls\n",string, string, wstring, wstring);

   wprintf(L"--Strings in field #2--\n%15S\n"

           L"%15.4hs\n   %s%15.3ls\n",string, string, wstring, wstring);

   // display real numbers

   printf("--Real numbers--\n   %f %.2f %e %E\n",fpnt, fpnt, fpnt, fpnt);

   // display pointer

   printf("\n--Address as--\n   %p\n", &count);

   printf("-------------------------------------------\n");

   printf("Study and compare to your source code...\n");

   return 0;

}

 

Program Example:

/* This program uses the printf_s() and wprintf_s() functions

 * to produce formatted output. */

#include <stdio.h>

 

int main(void)

{

   char   chs = 'h', *string = "JustAString";

   int    count = -4321;

   double fpnt = 324.4655;

   wchar_t wch = L'w', *wstring = L"UnicodeOrMultibyte";

   printf("-------------------The given data-----------------------\n");

   printf("The char: %c, string: %s, int: %d, double: %f\n"

         "wide char: %lc, wide string: %ls\n", chs, string, count, fpnt, wch, wstring);

   printf("\n--------------Various formatted output------------\n");

   /* display integers. */

   printf_s("--Integer formats--\n"

           " Decimal: %d  Justified: %.6d  Unsigned: %u\n",count, count, count, count );

   printf_s("--Decimal %d as--\n HEX: %Xh  C hex: 0x%x  Octal: %o\n",count, count, count, count );

   /* display in different radixes. */

   printf_s("--Digits 10 equal--\n   Hex: %i  Octal: %i  Decimal: %i\n",0x10, 010, 10 );

   /* display characters. */

   printf_s("--Characters in field #1--\n%7c%5hc%5C%5lc\n", chs, chs, wch, wch);

   wprintf_s(L"--Characters in field #2--\n%4C%5hc%5c%5lc\n", chs, chs, wch, wch);

   /* display strings. */

   printf_s("--Strings in field #1--\n%15s\n%15.4hs\n   %S%15.3ls\n",string, string, wstring, wstring);

   wprintf_s(L"--Strings in field #2--\n%20S\n%20.4hs\n   %s%20.3ls\n",string, string, wstring, wstring);

   /* display real numbers. */

   printf_s("--Real numbers--\n   %f, %.2f, %e, %E\n", fpnt, fpnt, fpnt, fpnt);

   /* display pointer. */

   printf_s("\n--\'count\' address--\n  %p\n", &count);

   printf("\nCompare to your source code....\n");

      return 0;

}

 

Question:

 

From the previous program example, study and find codes that you don’t understand. Then discuss with your class member and create five questions with answers based on the codes that you don’t understand.

 

More Story...

 

The printf() require an argument to be passed to it. It is a format string argument for example:

 

The code: printf("My name is Mr. C. Cplusplus\n");

 

The output: My name is Mr. C. Cplusplus

 

The format string is the string of characters enclosed between the double quotes, "", inside the pair of parentheses, (). The items inside the parentheses are used to pass arguments.

Delete all your previous code in the main() body. Then, try the following code snippet and see what the \n does.

printf("This is a line of code ");

printf("Another line\n of code. \nMore line of code \n");

printf("\n\nPlaying with code eh...\n");

 

Try other escape sequence, \t code by replacing the previous code with the following code.

printf("This is\ta real\tor what?\n");

printf("You\tmake\it\treal\you\know\n");

 

Next, try the following conversion specifier code. Study the output and compare it with the related source code.

char chr = 'N';

 

printf("My initial is %c\n", chr);

printf("My name is %s, I\'m %d years old\n", "Momok", 15);

printf("This is a character: \'%c\'\n", chr);

printf("This is a string: \"%s\"\n", "my string lol!");

printf("See my characters: %c, %c and %c\n", 'X', 'Y', 'Z');

printf("See my characters in integer: %d, %d and %d\n", 'X', 'Y', 'Z');

printf("See my characters in octal: %o, %o and %o\n", 'X', 'Y', 'Z');

printf("See my characters in hex: %0X, %0X and %0x\n", 'X', 'Y', 'Z');

printf("See my float and double: %f, %f\n", 1.234, 12.34567890);

printf("See my float and double precision: %.2f, %.7f\n", 1.234, 12.34567890);

 

Question:

 

From the previous program example, study and find codes that you don’t understand. Then discuss with your class member and create three questions with answers based on the codes that you don’t understand.

 

Questions And Activities:

 

1. How many ‘\n’s are needed to escape one blank line? Ans: 1

2. What is the effect of the ‘\t’ escape character? Ans: provide 1 horizontal tab

3. What was printed in place of %s format specifier? Ans: a string

4. What was printed in place of %c format specifier? Ans: a character

5. What was printed in place of %d format specifier? Ans: a decimal

6. What was printed in place of %f format specifier? Ans: a floating point number with default 6 precision

7. What %.3f means? Ans: a floating point number with 3 precision

8. From the code sample you can see that the decimal, octal, hexadecimal and character can be converted each other by using a proper format specifier. What are the format specifiers for octal and hexadecimal representatives? Ans: %o for octal and %x or %X for hexadecimal

9. Shows the output for the following codes.

 

printf("Get me %d \n tickets \n ", 10); printf("\n\n****\n ");
printf("Qty = %d \n ", 10); printf("Price = %.2f\n Total = %.2f\n", 2.25, 22.50);
printf("****\t******\t\n "); printf("\n***\t**\n ");
printf("***%c***\n ", ‘W’); printf("%s***\n", "TEST ");
Write a complete program for the following output.   Pass “handsome”, 20 and 70.45 as arguments.   I am handsome, 20 years old and my weight is 70.45 kg.	#include <stdio.h>   int main() {      char appearance[20];      int age = 0;      float weight = 0;      printf("Pass a string, an integer and a float:\n");      // scanf_s("%s %d %f", appearance, 19, &age, &weight);      //  a secure version      scanf("%s %d %f", appearance, &age, &weight);      printf("I am %s, %d years old and my weight is %.2f kg.\n",                                               appearance, age, weight);      return 0; }
Pass ‘R’, 321 and “Online” as argument.   The letter is R 321 is a whole number Online is a string	#include <stdio.h>   int main() {     char astring[20];     int whnum = 0;     char achar = ' '; // a space as an initial character value     // a secure version     // scanf_s("%c %d %s", &achar, 1, &whnum, astring, 19);     scanf("%c %d %s", &achar, &whnum, astring);     printf("The letter is %c\n%d is a whole number\n%s is a string\n",                                        achar, whnum, astring);     return 0; }
Write a complete C program that contains the following components.   printf(). 3 escape characters. 4 format specifiers.	#include <stdio.h>   int main() {     int anum = 70;     char achar = 'A';     double adouble = 1.234;     printf("A character: \"%c\",\tan integer: %d,\na"           " floating point number: %.4f and a hex: %0X.\n", achar, anum,                                                      adouble, anum); return 0; }
What wrong with the following codes if any, and how to correct it?   1.    #include <stdio.h>   int main() { printf("My first C class is very terrible!\n "); }	No return an integer such as return 0; statement. The main() return value is an integer as in int main(), so main() expect an integer to be returned.
2.    #include <stdio.h>   void main() { printf("My first C class is very terrible!\n "); return 0; }	The return 0; statement must be removed because main() doesn't have a return value denoted by the void keyword as in void main().

 

Supplementary Note - C Run-Time errno Constants

 

The #include <errno.h> preprocessor directive provides runtime errno constants. The errno values are constants assigned to errno in the event of various error conditions. errno.h contains the definitions of the errno values. However, not all the definitions given in errno.h are used in 32-bit Windows operating systems. Some of the values in errno.h are present to maintain compatibility with the UNIX family of operating systems. The errno values in a 32-bit Windows operating system are a subset of the values for errno in XENIX systems. Thus, the errno value is not necessarily the same as the actual error code returned by a system call from the Windows operating systems. To access the actual operating system error code, use the _doserrno variable, which contains this value. The following errno values are supported:

 

 

Finally, why you need to learn this Module? Ans: Just for fun!!! (this is one of the correct answers!)

 

 

 

 

 

| Main |< C main() and printf() functions 1 | C/C++ Variable, Operator & Type 1 >| Site Index | Download |

---

The C main() and printf() Functions:Part 1 |Part 2