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MODULE 2_1

C AND C++ CONSTRUCTS AND BASIC DATA TYPES 2

 

 

 

 

 

My Training Period: xx hours

 

Note: ANSI C refers to ISO/IEC C. The source code for this Module is: C & C++ source codes and the practice worksheets: C & C++ basic data types and the C & C++ standard input, scanf()/scanf_s().

 

The C/C++ programming skills that supposed to be acquired:   Able to understand and use the constant, character and escape sequence. Able to understand and use the C typecasting/promotion.   2.6     Escape Sequence The backslash (\) is called an escape character.  When the backslash is encountered, function such as printf() for example, will look ahead at the next character and combines it with the backslash to form an escape sequence, used in functions printf() and scanf(). Table 2.6 is the list of the escape sequence. Code Code Meaning \a Audible bell \t Horizontal tab \b Backspace \\ Backslash character \f Formfeed \’ Single quote character \n Newline \" Double quote character \r Carriage return \0 NULL, ASCII 0   Table 2.6:  Escape sequence For general C++ escape sequences are given in the following table.  Besides using the sequence, we also can use their value representation (in hexadecimal) for example \0x0A for newline.

 

 

2.7    Constants

• Values that do not change during program execution.

• Can be integer, character or floating point type.

• To declare a constant, use keyword const as shown in the following variable declaration example:

const  int   day_in_week = 7;

const  float   total_loan  =  1100000.35;

• Consider the following example. Compiler will generate error when we try to change the PI.

#include <stdio.h>

 

int main()

{

    const double PI = 3.14;

    double rad = 3.5;

   

    printf("Circle area = %.2f\n", PI*rad*rad);

    printf("Circle circumference = %.2f\n", 2*PI*rad);

    printf("Circle diameter = %.2f\n", 2*rad);

   

    // error C3892: 'PI' : you cannot assign to a variable that is const

    // PI = 3.14 + 5.0;

    return 0;

}

 

A sample output:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2.8    Character and String Constants

• A character constant is any character enclosed between two single quotation marks (' and ').

• When several characters are enclosed between two double quotation marks (" and "), it is called a string.

• Character constants examples:

'$'    '*'    ' '    'z'    'P'

• String constants examples, note that the blank space(s) considered as string:

"Name:   "

"Type of Fruit"

"Day:  "

      "   "

• You will learn other aggregate or derived data type specifiers such as struct, union, enum and typedef in other Modules or in the program examples.

2.9    C Typecasting and Type Promotion

• During the program development, you may encounter the situations where you need to convert to the different data type from previously declared variables, as well as having mixed data type in one expression.

• For example, let say you have declared the following variables:

int total, number;

float average;

• But in the middle of your program you encountered the following expression:

average = total / number;

• This expression has mixed data type, int and float.  The value of the average will be truncated, and it is not accurate anymore.   Many compilers will generate warning and some do not, but the output will be inaccurate.

• C provides the unary (take one operand only) typecast operator to accomplish this task.  The previous expression can be re written as

average =  (float) total / number;

• This (float) is called type cast operator, which create temporary floating-point copy of the total operand.  The construct for this typecast operator is formed by placing parentheses around a data type name as:

(type) such as  (int), (float) and (char).

 

In an expression containing the data types int and float for example, the ANSI C standard specifies that copies of int operands are made and promoted to float. The cast operator normally used together with the conversion specifiers heavily used with printf()/printf_s() and scanf()/scanf_s().  C’s type promotion rules specify how types can be converted to other types without losing the data accuracy. The promotion rules automatically apply to expressions containing values of two or more different data type in mixed type expression.  The type of each value in a mixed-type expression is automatically promoted to the highest type in the expression. Implicitly, actually, only a temporary version of each new value (type) is created and used for the mixed-type expression, the original value with original type still remain unchanged. Table 2.8 list the data types in order from highest to lowest type with printf and scanf conversion specifications for type promotion From the same table, type demotion, the reverse of type promotion is from lowest to highest.  Type demotion will result inaccurate value such as truncated value.  Program examples for this section are presented in formatted file input/output Module. This issue is very important aspect to be taken care when developing program that use mathematical expressions as well as when passing argument values to functions. C++ has some more advanced features for typecasting and will be discussed in Typecasting Module.

• Basically, the C data types fall into general categories. The "integral types" include char, int, short, long, signed, unsigned, and enum. The "floating types" include float, double, and long double. The "arithmetic types" include all floating and integral types.

• Conversion of an operand value to a compatible type causes no change to the value or the representation. For example, from int to int and float to float. However for different type in same category such as the arithmetic types, the narrow conversion will lose the precision. For example from float to int and from double to float.

• Explicit and implicit type conversion example:

#include <stdio.h>

 

int main()

{

      short a = 30;

      int b = 200;

      // use f or F to force to float

      float c = 300.34F;

      double d = 10000.99;

 

      // narrow conversion, compiler warning

      // warning C4244: '=' : conversion from 'double' to 'float', possible loss of data

      c = d + d;

      // warning C4244: '=' : conversion from 'double' to 'float', possible loss of data

      b = c + c;

      printf("c = %.2f\n", c);

      printf("b = %d\n", b);

 

      // explicit conversion, may lose precision, no compiler warning

      c = (float)(d + d);

      d = (double)(c + c);

      printf("\nc = %.2f\n", c);

      printf("b = %d\n", b);

 

      // wide conversion, it is OK

      b = a + a;

      d = c + c;

 

      printf("\nb = %d\n", b);

      printf("d = %.2f\n", d);

 

      return 0;

}

 

A sample output:

• The mixed integer and float for division issue. Study the source code and the output.

#include <stdio.h>

 

int main()

{

      float p = 0.0;

      int r = 4, s = 5;

      // integer division gives an integer result. Mixed integer and floating

      // point expression give a  floating point result.

      //

      // make sure the format specifier is matched

      //

      // implicit conversion

      printf("3/2 = %d\n", 3/2);

      printf("\n3.0/2.0 = %.2f\n", 3.0/2.0);

      printf("\n3/2.0 = %.2f\n", 3/2.0);

      printf("\n3.0/2 = %.2f\n", 3.0/2);

      printf("\n1/2 = %d\n", 1/2);

      // explicit conversion

      printf("\n(float)3/2 = %.2f\n", (float)3/2);

      p = r/s;

      // warning C4244: '=' : conversion from 'int' to 'float', possible loss of data

      // fraction part has been discarded

      printf("\np = r/s = %.2f\n", p);

      p = (float)r/s;

      printf("\np = (float)r/s = %.2f\n", p);

      return 0;

}

 

A sample output:

 

• The following Table list format specifiers used in standard input and output C functions for VC++.

• Sometime you may find a length modifier as listed in the following table.

• The following table is a list of the ANSI C formatted output conversion of the printf()/printf_s() function, used with %.  The program examples are presented in C Formatted Input/Output.

• The following table is a list of ANSI C formatted input conversion of the scanf()/scanf_s() function. We will learn more detail about this in another Module.

 

C & C++ programming tutorials

 

 

 

 

 

Further C and C++ reading and digging:

1. The ASCII, EBCDIC and UNICODE character sets reference Table can be found here: Character sets Table.
2. Check the best selling C/C++ books at Amazon.com.

 

 

 

 

 

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