Table of contents
1. Definition, initialization, input and output
1. Characters
Type: char
Input: getchar
Output:putchar
Example:
#include <stdio.h>
void main()
{
char ch;
while (ch = getchar())
{
if (ch == EOF)break;
printf("%d", ch);
putchar(ch);
}
return;
}Running results: (8 lines)
a^Zb
97a
26
a
97a
10
^Zexplain:
Enter a^Zb and press Enter, enter the two characters a and ^Z, then enter a and press Enter, enter the two characters a and the newline character, and then enter ^Z. The program ends.
Note 1:
The ASCII code of '\0' is 0, the ASCII code of '^A' - '^Z' is 1-26, of which the newline character '\n' is 10, and the '^Z' is 26, but when the input buffer When '^Z' appears after '\n' when the area is empty, the ASCII code of '^Z' is -1, indicating the end of file.
Note 2:
EOF is a constant -1, and OJ input and output are often controlled by EOF.
Note 3:
No. 10 '\n' and No. 26 '^Z' are both truncation of getchar. Enter a line of string, getchar can only read the first '\n' or '^Z', and discard any remaining ones.
2. C language string
1. Representation of string
In C language, strings are represented by char arrays, and '\0' is added to the end of the string to indicate the end.
2. Input and output
Input: gets
Output:puts
Example:
#include <stdio.h>
#include<string.h>
void main()
{
char str[]="abcde";
puts(str);
gets(str);
printf("%d\n", strlen(str));
puts(str);
return;
}Running result 1: (4 lines)
abcde
^Za
5
abcdeRunning result 2: (5 lines)
abcde
a^Zb
2
a?It can be seen that the newline character and ^Z are both truncation of the gets function. The difference is that
The newline character will be read and discarded by gets, and gets handles ^Z in the same way as getchar. When the buffer is empty, it is the -1 character, and when the buffer is not empty, it is the 26th character.
3. Commonly used functions
(1) strcat function-string connection
string catenate string concatenation
Example:
#include <stdio.h>
#include<string.h>
void main()
{
char str1[10] = "ab";
char str2[] = "cd";
printf("%d %d\n", strlen(str1), strlen(str2));
strcat(str1, str2);
printf("%d %d\n", strlen(str1), strlen(str2));
printf("%s %s", str1, str2);
return;
}operation result:
2 2
4 2
abcd cdThe strcat(str1, str2) function copies str2 to the back of str1.
(2) strcpy and strncpy functions - string copy
strcpy(str1,str2) copies str2 to the location of str1
strncpy(str1,str2,n) copies the first n characters of str2 to the position of str1
(3) strcmp function - string comparison
strcmp(str1,str2) is compared in lexicographic order, and the return values >0, =0, and <0 respectively represent str1>str2, str1==str2, str1<str2
(4) strlen and sizeof - string length
sizeof is a keyword and calculates the length of the array
strlen is a function that calculates the number of characters in a string, excluding '\0'
(5) strlwr and strupr functions - string case
strlwr converts uppercase letters into lowercase letters
strupr converts lowercase letters into uppercase letters
Summary: C-style string input - cin or getline or get, cin ends with a space or newline, getline and get both read one line.
The getline function will read and discard the newline characters, while the get function will keep the newline characters in the input buffer if it takes parameters. The get function can read and discard the newline characters if it takes no parameters.
Three, string class
1. Definition, initialization, input and output
#include<iostream>
#include<string>
using namespace std;
int main()
{
string str="abc";
cin>>str;
cout<<str;
return 0;
}2. String assignment, length calculation, and flipping
#include<iostream>
#include<string>
using namespace std;
int main()
{
string str1="abc";
string str2=str1;
reverse(str2.begin(),str2.end());
cout<<str1<<" "<<str1.length()<<" "<<str2;
return 0;
}3. Get characters from string
It can be in array form or iterator form.
#include<iostream>
#include<string>
using namespace std;
int main()
{
string str="abcde";
cout<<str[2];
string::iterator it=str.begin();
cout<<*it;
it=str.end()-1;
cout<<*it;
return 0;
}Output:
cae
4. Comparison and connection of strings
#include<iostream>
#include<string>
using namespace std;
int main()
{
string str1="abc",str2="def",str3="def";
if(str1<str2)cout<<"str1<str2\n";
if(str2==str3)cout<<"str2=str3\n";
cout<<str1+str2;
return 0;
}Output:
str1<str2
str2=str3
abcdef
5. Convert string to character array
#include<iostream>
#include<string>
using namespace std;
int main()
{
string str="abc";
const char *p1=str.c_str();
char *p2=new char[20];
strcpy(p2,p1);
cout<<p2;
return 0;
}6. Find characters in string
#include<iostream>
#include<string>
using namespace std;
int main()
{
string str="abca";
cout<<str.find('a')<<" "<<str.find('a',2);
return 0;
}Output:
0 3
Attached are the common string functions in the C++ textbook:
