A c \ C ++ exam IV every day --- flip a string

This is also a classic C language in the test: Given a string, flip it. For example, abc => when CBA got this question, I didn't want to think about it. Simply put, I used a string tmp to cache this string and then assigned a value for a for loop. The code will be available if you have ideas. [Cpp] # include <stdio. h> # include <stdlib. h> int main () {char string [20], tmp [20]; int length; printf ("please input less than 20 char :"); scanf ("% s", string); printf ("your input string is % s \ n", string); length = strlen (string ); printf ("length is % d \ n", length); for (int I = 0; I <length; ++ I) {tmp [I] = string [I];} for (int I = 0; I <length; ++ I) {string [I] = tmp [length-i-1];} printf ("after revert: % s \ n", s Tring); return 0;} compile with gcc: gcc-o revert revert_string.c-std = c99 and run the command. The result is as expected. However, my algorithm is not elegant, because I use a loop to assign values to two character arrays and then use a loop to flip the array. This efficiency is not flattering. The elegant method should be like this: Find the middle position of the string, and then swap the character on the left with the character on the right. The implementation should be as follows: [cpp] # include <stdio. h> # include <stdlib. h> int main () {char string [20], tmp; int length; printf ("please input less than 20 char:"); scanf ("% s ", string); printf ("your input string is % s \ n", string); // get string length, very useful method for (length = 0; string [length]; length ++); printf ("length is % d \ n", length); // very beateful !!! For (int I = 0; I <length/2; I ++) {tmp = string [I]; printf ("tmp is % c \ n ", string [I]); string [I] = string [length-i-1]; printf ("string [% d] is % c \ n", I, string [length-i-1]); string [length-i-1] = tmp; printf ("string [% d] is % c \ n", length-i-1, tmp);} printf ("after revert: % s \ n ", string); return 0;} running effect: [plain] D: \ workspace \ C \ revert_string> gcc-o revert revert_string.c-std = c99 D: \ workspace \ C \ revert_string> rev Ert please input less than 20 char: abc your input string is abc length is 3 tmp is a string [0] is c string [2] is a after revert: CBA D: \ workspace \ C \ revert_string> revert please input less than 20 char: abcd your input string is abcd length is 4 tmp is a string [0] is d string [3] is a tmp is B string [1] is c string [2] is B after revert: algorithms such as dcba are much more efficient than before. As long as you use your brains, the world will become more elegant.