shift a string to right and left in O(n) time and O(1) memory

strshift.cpp

#include <cstring>
#include <cstdlib>
#include <iostream>

using namespace std;

inline int rightshiftindex(int index,int offset, int len){
    if(index+offset>=len){
        return (index+offset)-len;
    }
}
void _strrightshift(char *str, int offset, int len){
    char tmp_latter,tmp;
    char count;
    int index,index_next_round;
    int curr_start=0;
    index=curr_start;
    tmp_latter=str[curr_start];
    while(true){
        if(count>=len){
            break;
        }
        index_next_round=rightshiftindex(index,offset,len);

        tmp=str[index_next_round];
        str[index_next_round]=tmp_latter;
        tmp_latter=tmp;
        ++count;
        index=rightshiftindex(index,offset,len);
        if(index==curr_start){
            curr_start=++index;
            tmp_latter=str[curr_start];
        }
    }
}
void _strleftshift(char *str, int offset, int len){
    int count=0; //已经转换了多少字符
    int curr_start=0; //本轮开始的index
    int index=curr_start;
    int next_index;
    char first_tmp;
    while(true){
        if(count>=len){
            break;
        }
        if(index==curr_start){
            first_tmp=str[index];
        }
        next_index=rightshiftindex(index,offset,len);
        if(next_index==curr_start){
            str[index]=first_tmp;
        }else{
            str[index]=str[next_index];
        }
        index=next_index;
        ++count;
        if(index==curr_start){
            curr_start=++index;
        }
    }
}
void strrightshift(char *str, int offset, int len=0){
    if(len==0){
        len=strlen(str);
    }
    offset=offset%len;
    if(offset>len/2){
        _strleftshift(str,len-offset,len);
    }else{
        _strrightshift(str,offset,len);
    }
}
void strleftshift(char *str, int offset, int len=0){
    if(len==0){
        len=strlen(str);
    }
    offset=offset%len;
    if(offset>len/2){
        _strrightshift(str,len-offset,len);
    }else{
        _strleftshift(str,offset,len);
    }
}
int main(int argc, const char *argv[])
{
    char a[100];
    char b[16];
    strcpy(a,argv[1]);
    strcpy(b,argv[2]);

    strrightshift(a,atoi(b));
    cout<<a<<endl;
    strleftshift(a,atoi(b));
    cout<<a<<endl;
    return 0;
}