LeetCode: Valid Number

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

   bool isNumber(const char *s) {  
     int n = strlen(s);  
     int i = 0;  
     while(i<n && (s[i] == ' ' || s[i] == '\t'))i++;  
     if(i==n)return false;  
     int j = n-1;  
     while (j >= 0 && (s[j] == ' ' || s[j] == '\t'))j--;  
   
     s = s+i;  
     n = j-i+1;  
     if (n == 1)if(s[0] <='9' && s[0] >= '0')return true; else return false;  
   
     if (s[0] == '-' || s[0] == '+'){s++;n--;}  
     if (s[n-1] == '+' || s[n-1] == '-')return false;  
   
     bool res = true, dot = false, exp = false, number = false, sign = false;  
   
     for (i = 0; i < n; i++)  
     {  
       if(i==0 && (s[i] == '+' || s[i] == '-')){return false;}  
       else if ((s[i] == '+' || s[i] == '-') && s[i-1] != 'e') {return false;}  
       else if (s[i] == '+' || s[i] == '-')if(sign)return false; else sign = true;  
       else if(s[i] == '.'){  
         if (exp == true)return false;  
         if(dot == false)dot = true;  
         else return false;  
       }  
       else if (s[i] == 'e')  
       {  
         if (dot == true && number == false)return false;  
         if (i==0 || i== n-1 || exp == true)return false;  
         exp = true;  
       }  
       else if (s[i] < '0' || s[i] > '9'){return false;}  
       else number = true;  
     }  
   
     if(number == false)return false;  
   
     return res;  
   }