View Compilation Error

0_0_19369280_1716.cpp:4:11: error: '::main' must return 'int'
 void main()
           ^
0_0_19369280_1716.cpp: In function 'int main()':
0_0_19369280_1716.cpp:21:19: error: 'strstr' was not declared in this scope
    w=strstr(a[j],s);
                   ^