题目描述：
Given an integer, return its base 7 string representation.
Example 1:
Input: 100
Output: “202”
Example 2:
Input: -7
Output: “-10”
Note: The input will be in range of [-1e7, 1e7].
代码实现：
class Solution {
public:
string convertToBase7(int num) {
string str="";
int nega=0;
if(num<0){
nega = 1;
num = abs(num);
}
while(num/7){
str+=to_string(num%7);
num/=7;
}
str+=to_string(num%7);
if(nega){
str+="-";
}
reverse(str.begin(),str.end());
return str;
}
};