View Compilation Error

0_0_21507282_3379.cpp:18:12: error: 'string' was not declared in this scope
 int change(string)
            ^
0_0_21507282_3379.cpp:19:1: error: expected ',' or ';' before '{' token
 {
 ^
0_0_21507282_3379.cpp: In function 'int main()':
0_0_21507282_3379.cpp:39:24: error: 'change' cannot be used as a function
    a[i].harm=change(lev);
                        ^