Sometimes you do and sometimes you don't.

ADDING and SUBTRACTING in BASIC MATH is different from
ADDING and SUBTRACTING in ALGEBRA.

Sometimes to ADD in ALGEBRA, you ADD in BASIC MATH, and sometimes you
SUBTRACT in BASIC MATH.

(+7) + (+3) like signs, ADD 7+3 in BASIC MATH, get 10, keep the + sign.
Answer: +10.

(-7) + (-3) unlike signs, ADD 7+3 in BASIC MATH, get 10, keep the - sign.
Answer: -10,

(+7) + (-3) unlike signs, SUBTRACT 7-3 in BASIC MATH, get 4, 7 is larger than 3, so use the sign of 7 which is +
Answer: +4

(-7) + (+3) unlike signs, SUBTRACT 7-3 in BASIC MATH, get 4, 7 is larger than 3, so use the sign of 7 which is -
Answer: -4

Edwin