View Compilation Error

0_0_19772406_25386.cpp: In function 'int main()':
0_0_19772406_25386.cpp:67:22: error: 'strlen' was not declared in this scope
   int len=strlen(str3);
                      ^
0_0_19772406_25386.cpp:72:27: error: 'memset' was not declared in this scope
   memset(str,0,sizeof(str));
                           ^
0_0_19772406_25386.cpp:75:18: error: 'strcpy' was not declared in this scope
   strcpy(str1,str);
                  ^
0_0_19772406_25386.cpp:89:23: error: 'strcmp' was not declared in this scope
    if(strcmp(str1,str2)==0)
                       ^