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-------------------------------------------------------------------------------- C REFERENCE CARD LATTICE C GARY COOMBS -------------------------------------------------------------------------------- ESCAPE CHARACTERS newline NL (LF) \n tab HT \t backspace BS \b carriage return CR \r form feed FF \f backslash \ \\ single quote ' \' double quote " \" bit pattern ddd \ddd ------------------------------------------------------------------------------- PRINTF() CONVERSIONS AS RELATED TO STRINGS |%10s| |hello, world| |%-10s| |hello, world| |%20s| | hello, world| |%-20s| |hello, world | |%20.10s| | hello, wor| |%-20.10s| |hello, wor| ------------------------------------------------------------------------------- STORAGE CLASSES I. Keywords: auto, external, static, register II. General Comments: The storage class of a variable determines its scope and how long the variable persists. Storage class is determined by where the variable is defined and by the associated keyword. Variables defined outside a function are external and have global scope. Variables declared inside a function are automatic and local unless one of the other keywords is used. External variables defined above a function are known to it even if not declared internally. 'auto' and 'register' variables are created each time the function containing them is evoked, and they vanish each time the function finishes. The others last for the duration of the whole program. III. Properties: STORAGE CLASS KEYWORD DURATION SCOPE automatic auto temporary local register register temporary local static static persistent local ................................................................................ external extern persistent global (all files) external static static persistent global (one file) Those above the dotted line are declared inside a function. Those below the line are defined outside a function. -------------------------------------------------------------------------------- BASIC DATA TYPES Keywords: int, long, short, unsigned, char, float, double Signed Integers --- These can have positive or negative values. int: the basic integer type for a given system long or long int: 32 bit integer short or short int: 16 bit integer Unsigned Integers --- zero or positive values only unsigned int:, unsigned long:, unsigned short: char: symbols 8 bits long Floating Point --- can have positive or negative values float: basic floating point 32 bits double or long float: 64 bits ------------------------------------------------------------------------------- IF STATEMENT FOR MAKING CHOICES Keywords: if, else General Comments: In each of the following forms, the statement can be either a simple statement or a compound statement. A "true" expression, more generally, means one with a nonzero value. Form 1: if ( expression ) statement; The statement is executed if the expression is true. Form 2: if ( expression ) statement1; else statement2; If the expression is true, statement1 is executed, else statement2 is executed. Form 3: if ( expression1 ) statement1; else if ( expression2 ) statement2; else statement3 If expression1 is true, then statement1 is executed. If expression1 is false but expression2 is true, statement2 is executed. Otherwise, if both expressions are false, statement3 is executed. ------------------------------------------------------------------------------- LOGICAL EXPRESSIONS expression1 && expression2 is true if and only if both expressions are true expression1 || expression2 is true if either one or both expressions are true !expression is true if the expression is false, and vice versa 6 > 2 && 3 == 3 is true ! ( 6 > 2 && 3 == 3 ) is false x != 0 && 20/x < t the second expression is evaluated only if x is nonzero ------------------------------------------------------------------------------- THE CONDITIONAL OPERATOR ?: This operator takes three operands, each of which is an expression. They are arranged this way: expression1 ? expression2 : expression3. The value of the whole expression equals the value of expression2 if expression1 is true, and equals the value of expression3 otherwise. ( 5 > 3 ) ? 1 : 2 has the value 1 ( 3 > 5 ) ? 1 : 2 has the value 2 ( a > b ) ? a : b has the value of the larger of a or b ------------------------------------------------------------------------------- MULTIPLE CHOICE WITH SWITCH Program control jumps to the statement bearing the vlaue of expression as a label. Program flow then proceeds through the remaining statements unless redirected again. Bothe expression and labels must have integer values (type char is included), and the labels must be constants or expressions formed solely from constants. If no label matches the expression value, control goes to the statement labeled default, if present. Otherwise control passes to the next statement following the switch statement. Form: switch (expression) { case label1 : statement case label2 : statement default : statement } Example: switch (letter) { case 'a' : case 'e' : printf("%d is a vowel\n", letter); case 'c' : case 'n' : printf("%d is in \"cane\"\n", letter); default : printf("Have a nice day.\n"); } If letter has the value 'a' or 'e', all three messages are printed; 'c' and 'n' cause the last two to be printed. Other values print just the last message. ------------------------------------------------------------------------------- THE WHILE STATEMENT Creates a loop that repeats until the test expression becomes false, or zero. The while statement is an entry-condition loop; the decision to go through one more pass of the loop is made before the loop is traversed. Thus it is possible that the loop is never traversed. The statement part of the form can be a simple statement or a compound statement. Form: while ( expression ) statement The statement portion is repeated until the expression becomes false or zero. Examples: while ( n++ < 100 ) printf("%d %d\n", n, 2*n+1); while ( fargo < 1000 ) { fargo = fargo + step; step = 2 * step; } ------------------------------------------------------------------------------- THE FOR STATEMENT The for statement uses three control expressions, separated by semicolons, to control a looping process. The initialize expression is executed once, before any of the loop statements are executed. If the test expression is true (or non-zero), the loop is cycled through once. Then the update expression is evaluated, and it is time to check the test expression again. The for statement is an entry-condition loop; the decision to go through one more pass of the loop is made before the loop is traversed. Thus it is possible that the loop is never traversed. The statement part of the form can be a simple statement or a compound statement. Form: for ( initialize; test; update ) statement; The loop is repeated until test becomes false or zero. Example: for ( n = 0; n < 10; n++ ) printf(" %d %d\n", n, 2*n+1 ); ------------------------------------------------------------------------------- THE DO WHILE STATEMENT The do while statement creates a loop that repeats until the test expression becomes false or zero. The do while statement is an exit-condition loop; the decision to go through one more pass of the loop is made after the loop is traversed. Thus the loop must be executed at least once. The statement part of the form can be a simple statement or a compound statement. Form: do statement; while ( expression ); The statement portion is repeated until the expression becomes false or zero. Example: do scanf("%d", &number); while (number != 20); ------------------------------------------------------------------------------- PROGRAM JUMPS I. Keywords: break, continue, goto II. General Comments: These three instructions cause program flow to jump from one location of a program to another location. III. break Can be used with any of the three loop forms and with the switch statement. It causes program control to skip over the rest of the loop or switch containing it and to resume with the next command following the loop or switch. Example: switch (number) { case 4 : printf("That's a good choice.\n"); break; case 5 : printf("That's a fair choice.\n"); break; default: printf("That's a poor choice.\n"); } IV. continue The continue command can be used with any of the three loop forms but not with a switch. It causes program control to skip the remaining statements in a loop. For a while or for loop, the next loop cycle is started. For a do while loop, the exit condition is tested and then, if necessary, the next loop cycle is started. Example: while ((ch = getchar()) != EOF) { if (ch == ' ') continue; putchar(ch); chcount++; } This fragment echoes and counts nonspace characters. IV. goto A goto statement causes program control to jump to a statement bearing the indicated label. A colon is used to separate a labeled statement from its label. Label names follow the rules for variable names. The labeled statement can come either before or after the goto. Form: goto label; . . . . label : statement Example: top : ch = getchar(); . . . . if (ch != 'y') goto top; ------------------------------------------------------------------------------- POINTER RELATED OPERATORS I. The Address Operator: & When followed by a variable name, gives the address of that variable. Example: &nurse is the address of the variable nurse. II. The Indirection Operator: * When followed by a pointer, gives the value stored at the pointed-to address. Example: nurse = 22; ptr = &nurse; val = *ptr; The net effect is to assign the value 22 to val. ------------------------------------------------------------------------------- FUNCTIONS I. Form: name(argument list) argument declarations function body The presence of the argument list and declarations is optional. Variables other than the arguments are declared within the body, which is bounded by braces. Example: diff(x,y) /* function name and argument list */ int x,y; /* declare arguments */ { /* begin function body */ int x; /* declare local variable */ z = x - y; return(z); /* return result to calling function */ } /* end function body */ II. Communicating Values: Arguments are used to convey values from the calling program to the function. If variables 'a' and 'b' have the values 5 and 2, then the call c = diff(a,b); transmits 5 and 2 to the variables x and y. The values 5 and 2 are called actual arguments, and the diff() variables x and y are called formal arguments. The keyword 'return' communicates one value from the function to the calling program. 'c' receives the value of x, which is 3 A function ordinarily has no effect upon the variables in a calling program. Use pointers as arguments to directly effect variables in the calling program. This may be necessary if you wish to communicate more than one value back to the calling program. III. Function Type: Functions must have the same type as the value they return. Functions are assumed to be of type int. If a function is of another type, it must be declared so in the calling program and in the function definition. Example: main() { float q, x, duff(); /* declare in calling program */ int n; . . . . . . q = duff(x,n) . . . . . . } float duff(u,k) /* declare in function definition */ float u; int k; { float tor; . . . . . . return(tor); /* returns a float value */ } ------------------------------------------------------------------------------- OPERATOR PRIORITIES OPERATORS (from high to low priority) () { } -> . ! ~ ++ -- - (type) * & sizeof(all unary) * / % + - << >> (bit shifts) < <= > >= == != & (bitwise and) ^ (bitwise not) d| (bitwise or) && || ?: = += -= *= /* %= ------------------------------------------------------------------------------- FORMATS FOR printf() printf(controlstring, expression1, expression2, . . . ); %d - print an integer %u - print an unsigned integer %f - print a floating-point number %e - print floating-point in exponential form %g - chooses %e or %f depending on number size %c - print a character %s - print a string %o - print unsigned octal integer %x - print unsigned hexadecimal integer Modifiers may be placed after the % to indicate field width, precision, justification, and if an int is long: %10d - print an integer in a field 10 spaces wide %5.2f - print 2 decimal places; field width = 5 %-6d - print an integer left justified %1d - print a long integer ------------------------------------------------------------------------------- FORMATS FOR scanf() The scanf() works much like printf(). Here are the main differences: 1. The arguments following the control string must be addresses. They can use the address operator, as in &n, or they can be array names, which are pointers to the first array element. 2. There is no %g option. 3. Both %e and %f work the same, accepting either format. 4. A %b conversion specification exists for reading short integers. Example: int n; char title[20]; scanf("%d %d", &n, title); ------------------------------------------------------------------------------- STRUCTURES A structure is a data object capable of holding more than one type of value. A structure template establishes the type of data the structure can hold. The structure definition is enclosed in braces. A structure tag gives a short-hand name for the form. A structure variable is one whose type is given by a structure template. The template nust include a tag or a variable name or both. No Tag: Here we declare a variable 'fish' to be a structure of the indicated form. No tag is used, and the variable name follows the structure definition: struct { float length; float weight; char name[40]; } fish; /* fish as a structure variable */ Tag: Alternatively, use a tag name before the opening brace, then use the tag name later in declaring the variable: struct critter { /* critter is the tag name */ float length; float weight; char name[40]; }; struct critter fish, seal; /* declaring two structures */ struct critter birds[5]; /* an array of 5 structures */ All the structures here are of the critter form. ------------------------------------------------------------------------------- STRUCTURE AND UNION OPERATORS I. The Membership Operator: This operator is used with a structure or union name to specify a member of that structure or union. If "name" is the name of a structure and "member" is a member specified by the structure template, then name.member identifies that member of the structure. The membership operator can also be used in the same fashion with unions. EXAMPLE: struct { int code; float cost; } item; item.code = 1265; This assigns a value to the "code" member of the structure "item". II. The Indirect Membership Operator: -> This operator is used with a pointer to a structure or union to identify a member of that structure or union. Suppose "ptrstr" is a pointer to a structure and that "member" is a member specified by the structure template. Then ptrstr->member identifies that member of the pointed-to structure. The indirect membership operator can be used in the same fashion with unions. EXAMPLE: struct { int code; float cost; } item, *ptrst; ptrst = &item; ptrst->code = 3451; This assigns a value to the "code" member of "item". The following three expressions are equivalent: ptrst->code item.code (*ptrst).code ------------------------------------------------------------------------------- FLOW CONTROL Loops: while loop: while (condition) statement; Example: while (i++ < 20) q = 2 * q; for loop: for (initialize; test; update) statement; Example: for (n = 0; n < 10; n++) printf("%d %d\n", n, 2*n-1); do while loop: do statement while (condition); Example: do printf("Hello, Molly\n"); while (i++ < 10); BRANCHING: if forms: I. if (expression) statement; II. if (expression) statement; else statement; III. if (expression) statement; else if statement; else statement; Example: if (amt > 400) rate = .0056; else rate = .0062; switch: switch (expression) { case label1 : statement1 case label2 : statement2 . . . . . default : statement } ------------------------------------------------------------------------------- CODE FRAGMENT TO COPY A STRING TO AN ARRAY char name[MAX]; int c, i; printf("Enter your name: "); for (i = 0; (c = getchar()) != '\n' && i < MAX - 1; ++i) name[i] = c; name[i] = '\0'; printf("Your name is: %s", name); ------------------------------------------------------------------------------- C FOOD TERMINAL INDEPENDENCE PACKAGE (TIP) Include the following header files, structure definition, and body. #include <dos.h> #include <tip.h> struct TDB tdb; /* structure needed whenever TIP is used. */ main() { tinit(); /* initializes TIP, clears the screen, and */ . . . . /* places the cursor at position 1,1 */ tterm(); /* terminates TIP */ } c = tgetc -- get a character tpush(c) -- push a character back char c; n = tputc(c,d,e) -- put a character to the screen n = tputs(s) -- put a character string to the screen int n; char c,d,e; char *s; tpos(v,h) -- move cursor to V-H coordinate tvpos(v) -- move cursor to V coordinate int v; int h; TO_CS /* Clear screen */ TO_MCH /* Move cursor home */ TO_MCU /* Move cursor up */ TO_MCD /* Move cursor down */ TO_MCR /* Move cursor right */ TO_MCL /* Move cursor left */ TO_IL /* Insert line */ TO_DL /* Delete line */ TO_IC /* Insert character */ TO_DC /* Delete character */ TO_ERL /* Erase rest of line */ TO_ERS /* Erase rest of screen */ TO_BPM /* Begin protect mode */ TO_EPM /* End protect mode */ TO_BPF /* Begin protect field */ TO_EPF /* End protect field */ TO_VN /* Set video normal */ TO_VR /* Set video reverse */ TO_VNU /* Set video normal, underlined */ TO_VRU /* Set video reverse, underlined */ TO_VNF /* Set video normal, flashing */ TO_VRF /* Set video reverse, flashing */ TO_MC /* Move cursor to V-H coordinate */ TO_MCV /* Move cursor to V coordinate */ TO_ESC /* Escape the next character */ TI_CAN /* Cancel input line */ TI_MCH /* Move cursor home */ TI_MCU /* Move cursor up */ TI_MCD /* Move cursor down */ TI_MCR /* Move cursor right */ TI_MCL /* Move cursor left */ TI_IL /* Insert line */ TI_DL /* Delete line */ TI_IC /* Insert character */ TI_DC /* Delete character */ TI_ERL /* erase rest of line */ TI_ERS /* erase rest of screen */ TI_PGU /* page up */ TI_PGD /* page down */ TI_MCE /* move cursor to end */ TI_F0 /* Function 0 */ TI_F1 /* Function 1 */ TI_F2 /* Function 2 */ TI_F3 /* Function 3 */ TI_F4 /* Function 4 */ TI_F5 /* Function 5 */ TI_F6 /* Function 6 */ TI_F7 /* Function 7 */ TI_F8 /* Function 8 */ TI_F9 /* Function 9 */ TI_FA /* Function a */ TI_FB /* Function b */ TI_FC /* Function c */ TI_FD /* Function d */ TI_FE /* Function e */ TI_FF /* Function f */ ------------------------------------------------------------------------------- STANDARD FORMS /******************************************************************************* * FILENAME.C -- * * * * * * * * * * * * * * * *******************************************************************************/ /*------------------------------------------------------------------------------ | include files | ------------------------------------------------------------------------------*/ /*------------------------------------------------------------------------------ | definitions | ------------------------------------------------------------------------------*/ /*------------------------------------------------------------------------------ | function declarations | ------------------------------------------------------------------------------*/ /*------------------------------------------------------------------------------ | structure declarations | | | | Value = pointer to the word being stored. | | NumOccur = counter of the number of times the word has occurred. | ------------------------------------------------------------------------------*/ /*------------------------------------------------------------------------------ | global variable declarations | ------------------------------------------------------------------------------*/ /*------------------------------------------------------------------------------ | | ------------------------------------------------------------------------------*/ /*---------------------------------------------------------------------------- | | ----------------------------------------------------------------------------*/ /*-------------------------------------------------------------------------- | | --------------------------------------------------------------------------*/ /*------------------------------------------------------------------------ | | ------------------------------------------------------------------------*/ /*---------------------------------------------------------------------- | | ----------------------------------------------------------------------*/ /*-------------------------------------------------------------------- | | --------------------------------------------------------------------*/ /* */