Bài giảng Lập trình C - Session 10: Strings

Strings Session 10 Objectives Explain string variables and constants Explain pointers to strings Perform string input/output operations Explain the various string functions Explain how arrays can be passed as arguments to functions Describe how strings can be used as function arguments String variables Strings are arrays of characters terminated by the NULL (‘\0’) character. String variables can be assigned string constants. A string constant is a sequence of characters surrounded by double quotes. The ‘\0’ null character is automatically added in the internal representation of a string. While declaring a string variable, allow one extra element space for the null terminator. Declaring string variables A typical string variable declaration is:. 	char str[10]; str is a character array variable that can hold a maximum of 10 characters including the null terminator.   String I/O operations-1 String I/O operations are carried out using functions from the standard I/O library called stdio.h The gets() function is the simplest method of accepting a string through standard input Input characters are accepted till the Enter key is pressed The gets() function replaces the terminating ‘\n’ new line character with the ‘\0’ character Syntax : 	gets(str); String I/O operations-2 The puts() function is used to display a string on the standard output device. Syntax : 	puts(str); The scanf() and printf() functions are used to accept and display mixed data types with a single statement. The syntax to accept a string is as follows: 	scanf(“%s”, str); The syntax to display a string is as follows: 	printf(“%s”, str); String Functions Functions for handling strings are found in the standard header file string.h. Few of the operations performed by these functions are: Concatenating strings Comparing strings Locating a character in a string Copying one string to another Calculating the length of a string The strcat() function Joins two string values into one. Syntax: 	strcat(str1, str2); Concatenates the str2 at the end of str1 The function returns str1 The strcmp() function Compares two strings and returns an integer value based on the results of the comparison. Syntax: 	strcmp(str1, str2); The function returns a value: Less than zero if str1str2 The strchr() function Determines the occurrence of a character in a string. Syntax: 	strchr(str, chr); The function returns a value: Pointer to the first occurrence of the character (pointed by chr) in the string, str NULL if it is not present The strcpy() function Copies the value in one string onto another Syntax: 	strcpy(str1, str2); The value of str2 is copied onto str1 The function returns str1 The strlen() function Determines the length of a string Syntax: 	strlen(str); The function returns an integer value for the length of str When an array is passed as an argument to a function, only the address of the array is passed The array name without the subscripts refers to the address of the array void main() 	{ 	int ary[10]; 	. 	. 	fn_ary(ary); 	. 	. 	} Passing Arrays to Functions-1 Passing Arrays to Functions-2 #include   void main() { int num[5], ctr, sum=0; int sum_arr(int num_arr[]); /* Function declaration */   	clrscr();   	for(ctr=0;ctr #include   void main() { char lines[5][20]; int ctr, longctr=0; int longest(char lines_arr[][20]); /* Function declaration */  	clrscr();  	for(ctr=0;ctrprev_len) 	l_ctr=i; /* Stores the subscript of the longer string */   	prev_len=new_len; 	}   	return l_ctr; 	/* Returns the subscript of the longest string */ } Sample output of the program Enter string 1: The   Enter string 2: Sigma   Enter string 3: Protocol   Enter string 4: Robert   Enter string 5: Ludlum   The longest string is Protocol Example of Passing Strings to Functions-4