Bash- add up two arrays variables' to third array's variable

Question

i have three arrays A, B, C . Array AB values are being parsed from file and i want them to add up into array C .

#!/bin/bash
i=0
A=()
B=()
C=()
while read line
do
  A[i]="$(echo $line| cut -d\  -f4)"
  B[i]="$(echo $line| cut -d\  -f11)"
  echo ${A[i]} " and " ${B[i]}
  # outputs correct values
  C[i]=`expr ${A[i]} + ${B[i]}`
  echo ${C[i]} 
  # no output
  i=$((i+1))
done < ~/file
exit 0

what is wrong with that assignment?

complete line from script:

hitEnd[i]=`expr ${hitLength[i]}+${hitStart[i]}`
echo "${hitEnd[i]}"
#no output

Answer 1

the line:

    C[i]=`expr ${A[i]} + ${B[i]}`

while give an error if one of the two operands is missing. If that is expected, ie having empty fields in the files, then:

   C[i]=$((${A[i]:-0}+${B[i]:-0}))

Should work.

Answer 2

The script look correctly. You may not construct the array correctly.

And always double quote the variable to avoid some error.