How can I align 2 arrays?

[Lucas]

Thanks, but I tried:

str a1=
1
2
6
7
8

str a2=
3
4
5
6
7

and the result:

a[0]= 1
a[1]=
a[2]= 2
a[3]=
a[4]=
a[5]= 6
a[6]=
a[7]= 7
a[8]=
a[9]= 8

b[0]=
b[1]= 3
b[2]=
b[3]= 4
b[4]= 5
b[5]=
b[6]= 6
b[7]=
b[8]= 7
b[9]=