View Compilation Error

0_0_21265381_12796.cpp: In function 'void mul(char*, char*, char*)':
0_0_21265381_12796.cpp:10:22: error: 'strlen' was not declared in this scope
     int lenx=strlen(x);
                      ^
0_0_21265381_12796.cpp:13:25: error: 'memset' was not declared in this scope
     memset(temp,0,1000*4);
                         ^
0_0_21265381_12796.cpp:28:14: error: '_strrev' was not declared in this scope
     _strrev(z);
              ^
0_0_21265381_12796.cpp: In function 'int main()':
0_0_21265381_12796.cpp:52:29: error: 'strlen' was not declared in this scope
                 dot=strlen(s)-dot;
                             ^
0_0_21265381_12796.cpp:59:24: error: 'memset' was not declared in this scope
         memset(t,0,1000);
                        ^
0_0_21265381_12796.cpp:63:25: error: 'strlen' was not declared in this scope
         len=int(strlen(t))-dot*n;
                         ^