111CMSC 212 – S07 (lect 4)AnnouncementsProgram #1– Due February 13th(not the 10thas stated on the project description)Reading– Chapter 7 & 8• skip 8.1.4– Chapter 9 & 10 (Thursday)2CMSC 212 – S07 (lect 4)Switch Statementswitch (expression) {case constant-expression:statement;break;….default:statement;break;}Execution starts at the constant-expression equal to the expression– Without the break, will continue to next statement!!!(expression) assumed to be an integer expressionDefault constant expression matches anything else223CMSC 212 – S07 (lect 4)Pointer VariablesHold an address of something else– its location in memory– usually an address to a specified type of spacetype * varname;– int * a;– char * b;Star does not distribute to other variable names– int *a, b;– int *x, *y;Get an address by using a &– int a = 6;– printf(“%d is at %p\n”, a, &a);Dereference also using a star– int a, *b;– a = 7;– b = &a;– printf(“%d and %d \n”, a, *b);4CMSC 212 – S07 (lect 4)Functionstype name (parameters) block– type: return type for the function– name: name of the function– parameters: a comma separated list of types and names– block: the code to run when the function is calledreturn; or return expression;– terminates a function at that point– expression is the value returned by the function– implicit termination335CMSC 212 – S07 (lect 4)Recursive FunctionsFunctions that call themselves – can be indirect: (a calls b) and (b calls a)Example:void binary_to_ascii(unsigned int value) {unsigned int quotient;quotient = value / 10;if (quotient != 0) {binary_to_ascii(quotient);}printf("%d", value % 10 + '0');}6CMSC 212 – S07 (lect 4)Function ArgumentsComma separated list of valuesAll parameters are passed by value– called function can modify values– arrays are passed by the address of their 0th element• modifying elements of array seen by calling functionCan pass address of variable to change valuesint foo(int *a) {*a = 3;}int x;foo(&x);447CMSC 212 – S07 (lect 4)Passing Parameters to Mainint main(int argc, char *argv[])– Normal declaration of main– argc – number of command line arguments• Includes command itself– argv – array of character strings of command argumentsExample– From command line: % myprog –file myfile– In the program:• argc == 3• argv[0] = “myprog”• argv[1] = “-file”• argv[2] = “myfile”8CMSC 212 – S07 (lect 4)Standard Type DefinitionsSeveral Types are defined in C's libraries– Defined in stddef.h– size_t - unsigned integer value (often int or long)– ptrdiff_t - signed value (used when subtracting pointers)Used by several standard routines– sizeof(<type>) returns a size_t for example559CMSC 212 – S07 (lect 4)C-StringsDefinition– An array of characters– Where the used portion is terminated by a null character<string.h>– Library that acts on C-strings– Most will crash if given something that does not fit the definition aboveCreating and Initializing a stringchar name1[4] = {‘J’,’a’,’n’,’\0’};char name2[6] = “Plane”;length of the string and the sizeof operator– sizeof operator tells the size of the variable or type– strlen uses the definition of C-string to find number of used characters10CMSC 212 – S07 (lect 4)StringsZero or more characters followed by null char ‘\0’– also called NUL– not counted as part of string– string.h defines prototypes for string routinesCopying Strings– size_t strlen(char const *str);• returns count of characters in str• up to but not including the null character– char *strncpy(char *dst, char const *src, size_t len);• copy src to dst• copy until ‘\0’ in src or at most len characters• pad extra characters will ‘\0’• Safety tip: dst[len-1] = '\0'; to force termination of new string– char *strncat(char *dst, char const *src, size_t len);• append src onto the end of dst• always appends NUL to end of dst string6611CMSC 212 – S07 (lect 4)String FunctionsComparison– int strncmp(char const *s1, char const s2, size_t len);• returns 0 if string equal up to len• returns a negative value if s1 is less than s2• returns a positive value if s1 is greater than s2Searching– char *strchr(char const *str, int ch);– char *strrchr(char const *str, int ch);• finds the first occurance of ch in str• strrchr finds the last occurance• returns NULL if not found– char *strstr(char const *s1, char const *s2);• find the first occurrence of s2 in s112CMSC 212 – S07 (lect 4)String Functions Exampleschar string[] = "this is a test string";char *ans;int length;length = strlen(string); /* returns 21 */ans = strchr(string, 'h'); /* returns string + 1 */ans = strrchr(string, 't'); /* returns string + 16 */ans = strstr(string, "test"); /* returns string + 10 */7713CMSC 212 – S07 (lect 4)Character FunctionsPrototypes in ctype.hClassifying characters – parameter is int, but it's a character– int isspace(int ch);• returns true if ch ' ', '\n', '\t', form feed, or carriage return– int isdigit(int ch);• returns true if its 0 through 9– int islower(int ch); and isupper(int ch);• return true if it’s a-z for islower and A-Z and isupper– int isalpha(int ch);• returns true if it's a-z or A-Z– int isalnum(int ch);• returns true if it's a-z or A-Z or 0-9Transformation– int toupper(int ch), int tolower(int ch)• converts to upper/lower
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