View Compilation Error

0_0_20874979_8486.cpp: In function 'int main()':
0_0_20874979_8486.cpp:4:152: error: 'memset' was not declared in this scope
 int main() {      int n,m,t,a[1001],b[2002],w,i,j;     scanf("%d",&n);     while(n--)     {          scanf("%d%d",&m,&t);         memset(b,-1,sizeof(b));         w=0;          for(i=0;i<m;i++)              scanf("%d",&a[i]);         for(i=m-1;i>=0;i--)             for(j=0;j<i;j++)                  b[abs(a[i]-a[j])]=abs(a[i]-a[j]);         for(i=0;i<2002;i++)         {              if(b[i]!=-1)             {                  w++;                 if(w==t)                 {                      printf("%d\n",b[i]);                     break;                 }             }         }     }      return 0; }
                                                                                                                                                        ^