[string] ranking of country names ----- problem solving notes

【 character string 】 Sort by country name

Description：

Sort the entered country names in dictionary order .

Input：

Multiple country names , Each row of a , No extra characters .

Output：

The result after sorting . Each line has a country name .

Sample Output：

China
Usa
United Kingdom

Sample Input：

China
United Kingdom
Usa

HINT：

The number of countries does not exceed 100 individual .
The number of characters in each country name shall not exceed 100.

Topic analysis ：

This topic examines the basic operation of string , The steps to solve the problem are as follows .
1. String read
2. String sort
3. String output

C Language source code ：

//
// Created by  Dawn in the morning  on 2019/12/10.
//
#include<stdio.h>
#include<string.h>

int counter = 0;          // Counter , Global variables are easy to operate 
// Improved bubble sort 
void Sort(char c[][100]) {
    
    int i, j;
    char temp[100];
    int flag = 1;        // Judge whether to exchange 
    int n = counter;
    int last = 0;
    while (flag == 1) {
    
        flag = 0;
        for (i = 0; i < n - 1; i++) {
    
            j = i + 1;
            if (strcmp(c[i], c[j]) > 0) {
    
                strcpy(temp, c[i]);
                strcpy(c[i], c[j]);
                strcpy(c[j], temp);
                flag = 1;
                last = j;
            }
        }
        n = last;   // Record the last exchange position .
    }
}
void main() {
    
    int i = 0;
    char c[100][100];
    while (gets(c[i]) != NULL) {
    
        i++;
        if (i == 100)break;
    }
    counter = i;    // Write down the number of read strings 
    Sort(c);
    for (i = 0; i < counter; i++) {
    
        puts(c[i]);
    }
}

1. Reading of string
Declare a character type two-dimensional array to access the country name , According to the title, the size is c[100][100];
Observe the sample input and find that there is a space in the middle of a country name ,United Kingdom This product is composed of two strings , So we used scanf When the function reads a string , encounter Space or A newline End reading . And space or Carriage returns are left in the buffer .
So use scanf() Reading spaces is a headache , It needs to be dealt with separately .
Fortunately, there is another function in the standard library to read strings gets(),
** The function prototype char gets(char str
function ： From standard input stdin Read a line , And store it in str In the string pointed to . When a newline character is read , Or at the end of the file , Stop reading . The newline character read at the end is automatically converted to ’\0’ Add to the end of the character array .
Return value ：
It can be seen that his return value is a character pointer .
When read successfully , Return and str Pointer with the same parameters .
When reading to the end of the file （EOF） Or when something goes wrong , return NULL.
So when reading the code ：

while (gets(c[i]) != NULL) {
        i++;
        if (i == 100)break;
    }

//while It is mostly used for loops that do not know the number of cycles .
gets(c[i])!=NULL explain gets Function successfully read , The cycle continues , When reading fails ,gets The function returns NULL, The loop ends .

2. String sorting
The sorting adopts the improved version of bubble sorting method .
utilize string Functions in the library strcpm(str1,str2) String comparison .
If the return value < 0, said str1 Less than str2.
If the return value > 0, said str2 Less than str1.
If the return value = 0, said str1 be equal to str2.

3. String output
Used here puts() function . The function is to output the string to the screen . When outputting, only ‘\0’ That is, the end of string flag will stop , And auto wrap .
A lot of convenience , We don't have to write line breaks ’\n’ 了 .