Chuỗi ký tự trong c

At all Enter made in c we"ve become familiar with how to lớn declare, entry & string in C simply. In this article we will talk more about the examples, homework chain .

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1. Overview

The string is treated as an array 1 dimensions of elements of type char as characters, numbers & any special characters such as +, -, *, /, $, #,...By convention, a sequence will be terminated by the null character (‘’ : Register turong).Example: string "Infoworld" stored as follows:

How to lớn store string

2. Some declaring, initialization string

We consider the following example:

// e.g about string - code by nguyenvanquan7826#include int main() // khai bao chuoi teo toi domain authority 50 ky tu char name<50>; printf("Hi, What is your name? My name is: "); gets(name); printf("Hi %s, welcome khổng lồ C language ", name); // khoi tao chuoi ngay trong khi khai bao char myLove<> = "Nguyen Thi Lap Lanh"; puts(myLove); return 0;Result:

Hi, What is your name? My name is: Nguyen Van quan lại Hi Nguyen Van Quan, welcome lớn C language Nguyen Thi sparkle

In the program on, I have used the function puts lớn print out the string Mylove, this is also a function to đầu ra string.

As above we can see is the declaration chain or medium chain then import declaration assigning values ​​to the string just right. However we can not declare then assign values ​​as follows:

char name<50>;name = "Nguyen Van Quan"; // errorWhere want to lớn declare then assign values, we must use the string copy function strcpy in library string.h to lớn save the values ​​as follows:

// e.g about string - code by nguyenvanquan7826#include #include int main() char name<50>; strcpy(name, "Nguyen Van Quan"); puts(name); return 0;

3. Some examples of strings in C

3.1 Example 1: Count the number of words in the string

Please enter a string & count the number of words in the string. VD chain “Nguyen Van Quan” have 3 from.

To vì this, we see each of the characters consecutively và diverging words with spaces. Therefore this article will be provided khổng lồ count the number of spaces in the string. If string 1 word, no spaces, strings 2 from there 1 spaces between 2 from that. N general is from, there will be n-1 spaces.

The next problem is how to count the spaces? Simple, It has been known as the first xuất hiện string is an array of characters, so we can browse the characters turn to lớn examining the chain of characters are spaces. But want khổng lồ browse all the characters in the string (character array) they must know the number of characters in the string (number of elements in the array).

Fortunately, in the library string.h we have a function khổng lồ get the length of the string as a function strlen. (str – string, only – length).

// e.g about string - code by nguyenvanquan7826#include #include // for strlen functionint main() { char s<50>; printf("Enter a string: "); gets(s); int i, count = 0; // count - bien dem so luong dau cach for (i = 0; i Pretty simple code, you read, understand and test nhé.

Yet we have a code on the note:

Because the string is an array of characters, should like to take ith character in the string s, then we as the array access is s.This example applies only when the larger chain length 0 & no extra white sign at the top, end or between words.Like loops above, we have conditions i , however the nature of a loop strlen again to lớn count the number of characters of the string s. So if we write directly on the conditions in each iteration, program must run the command loop strlen lớn count the number of characters of s. This is redundant and make the program run longer. So we will put 1 variable is the length of the string out as follows:

int len = strlen(s);for (i = 0; i

3.2 Example 2: Standardize the string

Please enter a string & remove all extra spaces at the top, Last & between words if.

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This problem is important for the problem of software, later when stored, đầu vào data is noteworthy lớn be standardized, no surplus or deficit caused errors in the process & seek.

The first character of the string s is space, then s<0> the spaces, we delete it as done.The characters between words if redundant ie s & s along the spaces. We removed 1 in 2 is ok, because the words will separated by 1 spaces should have retained 1 spaces.The characters at the over string is space, then we will remove it by assigning the last character is a null character "" is finished. Remember that the last character is the element of the array n a, so the character of the string is s< strlen(s) - 1 >.

The next problem is how to lớn delete 1 characters in the string? You look at the example above we use the string copy function, & to delete 1 or a number of characters in the string we will use this function, but will be used in the copy address.

To delete a character from i to lớn j characters in the string s, we command strcpy(&s, &s);. The essence is that we copy the address of s the address of s.

// e.g about string - code by nguyenvanquan7826#include #include int main() { char s<50>; printf("Enter a string: "); gets(s); // delete all space at start of string while( s<0> == ' ' ) strcpy(&s<0>, &s<1>); // delete all space at over of string while( s< strlen(s)-1 > == ' ') s< strlen(s)-1 > = ''; // delete all space between two word int i; for(i = 0; i Ok. You run nhé. Remember enter the string excess space at the beginning, final, between to lớn check.

A small question as exercises do more for you is lớn look at the code line i--; // why??? và think why this line? Why vì chưng i have lớn decrease 1?

4. Some functions on strings và characters

Int isalpha(int c) : kiểm tra the alphabetical characters are not.Int isdigit(int c) : kiểm tra digit character is not.Int islower(int c): kiểm tra lowercase characters are not.Int isupper(int c): check uppercase characters are not.Int iSPACE(int c): kiểm tra character is empty ( , spaces, ).

The string processing functions. (This function is located in the library string.h)

Int strlen(char * s) returns the length of the string s;Char * strupr(char * s) Change in lowercase to lớn uppercase string s.Char * strlwr(char * s) Change uppercase to lớn lowercase.Char * strcat(char * s1, char * s2) connection string to string s1 s2;Int strcmp(char * s1, char * s2) the negative value if the strings s1 and smaller string s2. And for the price refugee positive if greater string strings s1 s2. Returns the value of 0 if the string s1 with the string s2.Int strcmpi (char * s1, char * s2) compare 2 string but vì not distinguish lowercase & uppercase.Char * strcpy(char * s1, char * s2) copy string to lớn string s1 s2.Char * strncpy(char * s1, char * s2, int n) Copy the first n characters of string s2 to string s1Char * strnset(char * s ,int c, int n) n times to lớn copy the character c in string s.Char * strstr(char * s1, char * s2) look for the occurrence of the string s2 in the string s1. If you find the address of the function substring in string s1. In contrast to lớn NULL.Char * strrev(char * s) Using reverse s.Neu successful string functions khổng lồ address string reversed.

Exercise

Write a program separate from a given string name. VD named Nguyen Thi sparkling => separation FlaxWrite a program standardized own name string. CEO:ha noi => Ha Noi.Write the function switch 1 string to lowercase và 1 function converted lớn UPPERCASE.Write a program into a string of characters in the string and then count how many letters “of”.Write a program on a string. Kiểm tra if it is mirrored string? Symmetry is the string string when writing backwards and still like the original string. CEO levelWrite a program in numbers 3 number. Said the inscription describes the value of that number. Example 123 -> One hundred và twenty three.