View Compilation Error

0_0_37482346_26068.c: In function 'main':
0_0_37482346_26068.c:13:21: error: 'str' undeclared (first use in this function)
         a[i][strlen(str)]= ' ';
                     ^
0_0_37482346_26068.c:13:21: note: each undeclared identifier is reported only once for each function it appears in
0_0_37482346_26068.c:15:26: error: 'len' undeclared (first use in this function)
         for(k = 0 ; k <= len ; k++)
                          ^