原题：
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：
char* convertToBase7(int num) {
int test = abs(num);
char* result;
result=(char*)malloc(sizeof(char)*20);
*(result+19)='\0';
int n;
for(n=18;test!=0;n--)
{
*(result+n)=(char)(test%7+48);
test=test/7;
}
if(num==0)
{
*(result+n)='0';
return result+n;
}
if(num<0)
{
*(result+n)='-';
return result+n;
}
return result+n+1;
}
