字符串加解密:C语言解法

对于输入一行代表解密，一行代表加密的字符串可用 mod2 进行判断加密还是解密。 方法里对每个字符单独判断并转换，最后输出字符串。

#include<stdio.h>
void encryption_and_decrypt(char *str, int flag){
    int temp = 'a'-'A';
    int len = strlen(str);
    for(int i=0; i<len; i++){
        if(str[i]>='A' && str[i]<='Z'){
            if(!flag)
                str[i]=str[i]+1>'Z'?'a':str[i]+temp+1;
            else
                str[i]=str[i]-1<'A'?'z':str[i]+temp-1;
        }else if(str[i]>='a' && str[i]<='z'){
            if(!flag)
                str[i]=str[i]+1>'z'?'A':str[i]-temp+1;
            else
                str[i]=str[i]-1<'a'?'Z':str[i]-temp-1;
        }else if(str[i]>='0' && str[i]<='9'){
            if(!flag)
                str[i]=str[i]+1>'9'?'0':str[i]+1;
            else
                str[i]=str[i]-1<'0'?'9':str[i]-1;
        }
    }
    printf("%s\n",str);
}
int main(){
    int flag = 0;
    char str[1000] = {""};
    while(gets(&str)){
        encryption_and_decrypt(str, flag%2);
        flag++;
    }
}