字元、字串(C-style)

--- ###### tags: `sprout` --- # 字元、字串(C-style) *slide: https://hackmd.io/@r5gr22SqQZOKqVlTHWYDPg/HJdALJME8* *2020/03/21 丁緒慈* --- ## 字元 *什麼是字元* ---- 字元包含了 - 數字：0123456789 - 大寫英文字母：ABCDEFG... - 小寫英文字母：abcdefg... - 符號：#$%&()*+,-./:;<=>?@... **但不只這些！** ---- - 特殊字元，例如： - 換行 \n - tab \t ---- ### 宣告一個字元(character) ```cpp //宣告 char c; //給值 c = 'a'; //初始化 char ch = 'a'; ``` ---- ### 輸入輸出-1 ```cpp char c; cin>>c; cout<<c; ``` ---- ### 輸入輸出-2 怎麼輸出反斜線和引號 ```cpp cout<<'\'; //? cout<<'''; //? ``` ```shell error: missing terminating ' character ``` ---- 用反斜線輸出特殊符號 ```cpp cout<<'\\'; //output: \ cout<<'\''; //output: ' ``` ---- ### 電腦如何表達字元呢電腦只有0跟1欸 ---- #### ASCII編碼 ![ascii](https://www.w3resource.com/w3r_images/python-basic-image-exercise-86.png =800x500) ---- example 1: ```cpp int c = 'a'; cout<<c<<endl; //output: 97 int c = 97; cout<<char(c)<<endl; //output: a ``` example 2: ```cpp char c = 97; cout<<c<<endl; //output: a char c = 'a'; cout<<int(c)<<endl; //output: 97 ``` ---- 小練習用迴圈印出a~z (ascii code 97~122) (X) cout<<"abcdefghijklmnopqrstuvwxyz" ---- ```cpp #include<iostream> using namespace std; int main() { for(int i = 97; i<=122; ++i) cout<<char(i); return 0; } ``` ```cpp #include<iostream> using namespace std; int main() { for(char c = 'a'; c <= 'z'; ++c) cout<<c; return 0; } ``` ---- #### 既然字元是透過數字表達字元與數字間可以運算嗎例如：'p'+1, 'q'-2 ---- 可以 ```cpp char c = 'a'; cout<<c<<endl; c+=2; cout<<c<<endl; c-=1 cout<<c<<endl; ``` ---- ```cpp if('b'=='a'+1) cout<<"yes\n"; if(98=='a'+1) cout<<"correct\n"; ``` ---- #### 那字元與字元間呢？例如：'Q'-'P' ---- 也可以 ```cpp char c = 'z'; cout<<c-'a'<<endl; cout<<'c'+'A'-'b'-'B'<<endl; ``` ---- #### 還可以比大小 - 'a'<'b' (97<98) - 'A'<'a' (65<97) - '0'<'9' (48<57) ---- ### 小練習如果輸入大寫，就輸出小寫如果輸入小寫，就輸出大寫 ---- #### ~~--解法-1--~~ ```cpp if(c=='A') cout<<'a'; else if(c=='B') cout<<'b'; else if(c=='C') cout<<'c'; ... ``` ---- #### 解法-2: 觀察ASCII碼 | 大寫字元 | ASCII | 小寫字元 | ASCII | | -------- | ----- | -------- | ----- | | A | 65 | a | 97 | | B | 66 | b | 98 | | C | 67 | c | 99 | | ... | ... | ... | ... | | Z | 90 | z | 122 | ---- ```cpp char c; cin>>c; if(65<=c && c<=90) { c+=32; cout<<c; } else if(97<=c && c<=122) { c-=32; cout<<c; } ``` ---- #### 解法-3: 字元運算 ```cpp char c; cin>>c; if('A'<=c && c<='Z') { c+='a'-'A'; cout<<c; } else if('a'<=c && c<='z') { c-='a'-'A'; cout<<c; } ``` --- ## 字串(C-style) ---- 一個字元一個字元的說話很累耶 ```cpp char s = 's', p = 'p', r = 'r', o = 'o', u = 'u', t = 't'; cout<<s<<p<<r<<o<<u<<t; ``` ---- 把多個字元串在一起=>字串怎麼做？ ---- ### 字元陣列 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | |:--- |:--- |:--- |:--- |:--- |:--- |:---- | | 's' | 'p' | 'r' | 'o' | 'u' | 't' | '\0' | ---- | 0 | 1 | 2 | 3 | 4 | 5 | 6 | |:--- |:--- |:--- |:--- |:--- |:--- |:---- | | 's' | 'p' | 'r' | 'o' | 'u' | 't' | '\0' | - '\0'就像是字串的句點 - 在輸出字元陣列時，會輸出到'\0'為止 - 也就是說，'\0'後的字元不會被輸出 ---- 會輸出甚麼？ ```cpp char str[100] = "HelloWorld"; str[5] = '\0'; cout<<str; ``` ---- |0|1|2|3|4|5|6|7|8|9|10| |:-|:-|:-|:-|:-|:-|:-|:-|:-|:-|:-| |'H'|'e'|'l'|'l'|'o'|'W'|'o'|'r'|'l'|'d'|'\0'| |0|1|2|3|4|5|6|7|8|9|10| |:-|:-|:-|:-|:-|:-|:-|:-|:-|:-|:-| |'H'|'e'|'l'|'l'|'o'|'\0'|'o'|'r'|'l'|'d'|'\0'| <style> .y { color: yellow; } </style> ---- ### 宣告 ```cpp char str1[100] = "Hello"; char str2[] = "World"; char str3[100] = {'c', 'p', 'p', '\0'}; ``` ---- ### 輸入輸出 ```cpp char str[10]; cin>>str; //至多輸入?個字元 cout<<str; ``` ---- ### 大家來找碴 ```cpp char a[6] = "abcde"; char b[6]; b = a; cout<<b<<"\n"; ``` ```shell error: invalid array assignment ``` ---- 你會這樣做嗎 ```cpp int a[6] = {1, 2, 3, 4, 5, 6}; int b[6]; b = a; cout<<b<<"\n"; ``` 不會，所以字元陣列也不能這樣操作 ---- ```cpp char a[6] = "abcde"; char b[6]; for(int i = 0; i<6; ++i) b[i] = a[i]; cout<<b<<"\n"; ``` ---- ### 課堂練習 [217-凱薩密碼](https://neoj.sprout.tw/problem/217/) ---- | 輸入 | 輸出 || 輸入 | 輸出 | | :----: | :----: |-| :----: | :----: | | a | d || x | a | | b | e || y | b | | c | f || z | c | 輸入皆為小寫字母，位移3再輸出 ---- #### 解法 ```cpp #include<iostream> using namespace std; int main() { char str[600]; cin>>str; for(int i = 0; str[i]!='\0'; ++i) //TODO cout<<str<<"\n"; } ``` ---- ### 字串陣列 ```cpp char arr[3][4] = {"abc", "def", "ghi"}; //3個字串 //每個字串包含'\0'最多4字元 ``` | | 0 | 1 | 2 | 3 | | --- | --- | --- | --- | ---- | | 0 | 'a' | 'b' | 'c' | '\0' | | 1 | 'd' | 'e' | 'f' | '\0' | | 2 | 'g' | 'h' | 'i' | '\0' | ---- #### 輸入輸出 ```cpp char arr[3][10] for(int i = 0; i<3; ++i) cin>>arr[i]; for(int i = 0; i<3; ++i) cout<<arr[i]<<'\n'; ```