c语言凯撒密码、字母倒排序

凯撒密码：

#include <stdio.h>

int main() {
    char str[100], cipher[100];
    int key;
    printf("请输入需要加密的字符串：");
    fgets(str, 100, stdin);
    printf("请输入密钥：");
    scanf("%d", &key);
    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] >= 'a' && str[i] <= 'z') {
            cipher[i] = (str[i] - 'a' + key) % 26 + 'a';
        } else if (str[i] >= 'A' && str[i] <= 'Z') {
            cipher[i] = (str[i] - 'A' + key) % 26 + 'A';
        } else {
            cipher[i] = str[i];
        }
    }
    printf("加密后的字符串为：%s\n", cipher);
    return 0;
}

字母倒排序：

#include <stdio.h>
#include <string.h>

int main() {
    char str[100];
    printf("请输入一个字符串：");
    fgets(str, 100, stdin);
    int len = strlen(str);
    for (int i = len - 2; i >= 0; i--) { // 注意要减去1
        printf("%c", str[i]);
    }
    printf("\n");
    return 0;
}