Question

difference between msg[i+1] and msg[i]+1 ?

Answer 1

In an array msg[ ], msg[i+1] represents the value given to the index (i+1) of the array. 
msg[i]+1 takes the value stored in index i and adds 1 to it.

Answer 2

msg[i+1] means the index of array increase by 1
msg[i]+1 means the value at that index should increase by 1