View Compilation Error

0_0_28862712_6246.cpp:7:1: error: 'string' does not name a type
 string s;
 ^
0_0_28862712_6246.cpp: In function 'void levelOrder(BiNode*)':
0_0_28862712_6246.cpp:51:3: error: 's' was not declared in this scope
   s += p->data;
   ^
0_0_28862712_6246.cpp: In function 'int main()':
0_0_28862712_6246.cpp:69:3: error: 's' was not declared in this scope
   s = "";
   ^
0_0_28862712_6246.cpp:71:3: error: 'string' was not declared in this scope
   string ss1 = s;
   ^
0_0_28862712_6246.cpp:74:10: error: expected ';' before 'ss2'
   string ss2 = s;
          ^
0_0_28862712_6246.cpp:75:7: error: 'ss1' was not declared in this scope
   if (ss1 == ss2)
       ^
0_0_28862712_6246.cpp:75:14: error: 'ss2' was not declared in this scope
   if (ss1 == ss2)
              ^