After strcat, a [] = "ablmnp "and b [] = "lmnp". When entering the while loop,

i++-& gt； i = 1，b[ 1] = a[ 1] = b

i++-& gt； i =2，b[2]= a[2]= l；

b[3]= a[3]= m；

b[4]= a[4]= n；

b[5]= p；

B[0] = l has not changed, so lblmnp is output.