View Compilation Error

0_0_26319938_7708.cpp: In function 'int main()':
0_0_26319938_7708.cpp:23:23: error: 'memset' was not declared in this scope
   memset(a,0,sizeof(a));
                       ^
0_0_26319938_7708.cpp:36:23: error: 'strlen' was not declared in this scope
    int t=strlen(a[i].s);
                       ^
0_0_26319938_7708.cpp:39:19: error: 'strcpy' was not declared in this scope
    strcpy(x,a[i].s);
                   ^