rslt only keeps the value in last assignment . your  loop contains 4 assignment,and  can be expanded as follow:

rslt = {a[0],b[0]};

rslt = {a[1],b[1]};

rslt = {a[2],b[2]};

rslt = {a[3],b[3]};  //

Thanks Alpha, I know that's how it is working ,how can I modify the code to get the other three.Thanks 

try 

for (i = 0; i

Tanx Praveen Gudala,it sound logical but not working,for statement might not work for what I intend to use it for..it does not work the same way in hardware like software,it is use in hardware for initialization for all the variable to zero.I will come up wt something Insha Allah.