note <practical c programming> chapter 5

Practical C Programming                Chapter 5: Arrays, Qualitifiers, and Reading Numbers

1. Arrays:

    type array_name[length]; /* comment */
    to reference an element of an arrya, you use a number named index

2. Strings:

    Strings are sequences of characters
    the '\0'(NUL) is used to indicate the end of a string
    char string_name[length]; /* comment */
    C does not allow one array to be assigned to another, instead use the standard library function strcpy
        Function                            Description
        strcpy(string1, string2)    copy string2 into string1
        strcat(string1, string2)     concatenate string2 onto the end of string1
        length = strlen(string)      get the length of a string
        strcmp(string1, string2)    0 if string1 equals string2, otherwise nonzero

3. Reading Strings

    fgets(name, sizeof(name), stdin);
        name: the name of a character array. The line (including the end-of-line charavter) is read into this array;
        sizeof(name): indicates the maximum number of characters to read (plus one of the end-of-string character);
        stdin: the file to read

4. Multidimensional Arrays:

    type variable[size1][size2]; /* comment */
    C allows the programmer to use as many as dimensions as needed.

5. Reading numbers

    scanf provides a simple and easy way of reading numbers that almost never works.
    the scanf is notorious for its poor end-of-line handling, which makes scanf useless for all but an expert.
    Instead use fgets to read a line of input and sscanf to convert the text into numbrs.

        char line[256];        fgets(line, sizeof(line), stdin);        sscanf(line, format, &variable1, &variable2, ... );

6. Initializing variables

    C allows variable to be initialized in the declaration statement.

7. Types of Integers:

    long int
    short int
    signed int
    Integer printf/sscanf conversions
        %conversion    uses
        %hd                   (signed) short int
        %d                     (signed) int
        %ld                    (signed) long int
        %hu                   unsigned short int
        %u                     unsigned int
        %lu                    unsigned long int
    long int declarations allow the program to explicitly specify extra precision where it is needed (at the expense of memory).
    short int numbers save space but have a more limited range
    the most compact integers have type char, they also have the most limited range
    unsigned numbers provide a way of doubling the positive range at expense of elminating negative numbers.

8. Types of floats:

    float
    double
    long double
    float printf/sscanf conversions
        %conversion    uses               notes
        %f                       float                 printf only
        %lf                     double             scanf only
        %Lf                    long double    Not available on all compilers
    on some machines, single-precision, floating-point instructions execute faster (but less accurately) than double-precision instructions. Double-precision intructions gain accuracy at the expense of time and storage.
    In most cases, float is adequate; however, if accuracy is a problem, switch to double

9. Constant Declarations

    the keyword const indicates a variable that never changes
    const type VARIABLE = value; /* comment */
    constants must be initialized at declaration time and can never be changed.

10. Hexadecimal and Octal Constants

    leading zeros are used to signal an octal constant;
    staring a number with "0x" indicates a hexadecimal constant

11. operators for performing shortcuts

    ++ : used for incrementing
    -- : used for decrementing
    operator    shorthand    equivalent statement
    +=                x += 2;         x = x + 2;
    -=                 x -= 2;          x = x - 2;
    *=                 x *= 2;         x = x * 2;
    /=                 x /= 2;          x = x / 2;
    %=              x %= 2;        x = x % 2;

12. Side effects:

    a side effect is an operation that is performed in addition to the main operation executed by the statement.
    Never use ++ or -- as part of any other statement, and always put them on lines by themselves

13. ++x or x++

14. more side-effect problems

        value = 1;        result = (value++ * 5) + (value++ * 3);

    in order to avoid trouble and keep the program simple, always put ++ and -- on a line by themselves