Try (same as if operator precedence doesn't apply):
(1+2)-3
Then:
Switching +,-
: (1-2)+3=2
Switching +,x
: (1x2)-3=-1
Switching +,÷
: (1÷2)-3=-2.5
Switching -,x
: (1+2)x3=9
Switching -,÷
: (1+2)÷3=1
Switching x,÷
: (1+2)-3=0
Note: If anyone has more convoluted calculators, I'll post them as extra bonuses!
Bonus: brackets not allowed, operator precedence applies:
1+2-3
Then (assuming a 9-digit calculator):
Switching +,-
: 1-2+3=2
Switching +,x
: 1x2-3=-1
Switching +,÷
: 1÷2-3=-2.5
Switching -,x
: 1+2x3=7
Switching -,÷
: 1+2÷3=1.66666667
Switching x,÷
: 1+2-3=0
Second bonus: brackets not allowed, operator precedence applies, calculator breaks on recurring decimals:
1+2-4
Then:
Switching +,-
: 1-2+4=3
Switching +,x
: 1x2-4=-2
Switching +,÷
: 1÷2-4=-3.5
Switching -,x
: 1+2x4=9
Switching -,÷
: 1+2÷4=1.5
Switching x,÷
: 1+2-4=-1
Third bonus: operator precedence doesn't apply, calculator breaks on any decimal:
8+4-4
Then:
Switching +,-
: 8-4+4=8
Switching +,x
: 8x4-4=28
Switching +,÷
: 8÷4-4=-2
Switching -,x
: 8+4x4=48
Switching -,÷
: 8+4÷4=3
Switching x,÷
: 8+4-2=10
Fourth bonus: operator precedence does apply, calculator breaks on any decimal:
8+4-4
Then:
Switching +,-
: 8-4+4=8
Switching +,x
: 8x4-4=28
Switching +,÷
: 8÷4-4=-2
Switching -,x
: 8+4x4=24
Switching -,÷
: 8+4÷4=9
Switching x,÷
: 8+4-2=10
Fifth bonus (@Penguino): operator precedence does apply, calculator breaks on any decimal, tens digit unreadable:
9+9-3
Then:
Switching +,-
: 9-9+3= 3= ?3
Switching +,x
: 9x9-3= 78= ?8
Switching +,÷
: 9÷9-3=- 2=-?2
Switching -,x
: 9+9x3= 36= ?6
Switching -,÷
: 9+9÷3= 12= ?2
Switching x,÷
: 9+9-3= 15= ?5
Sixth bonus (@Rubio): Operator precedence doesn't apply, decimals work, last 4 digits in display and also the top bar of any digit don't work (i.e. 1=7 and 4=9), 8 digit display + sign:
10000+729-1728
Then:
Switching +,-
: 10000-729+1728= 10999= X ????
Switching +,x
: 10000x729-1728= 7288272= X28 ????
Switching +,÷
: 10000÷729-1728=-1714.2826=-X XXY.????
Switching -,x
: 10000+729x1728= 18539712= X 853 ????
Switching -,÷
: 10000+729÷1728= 6.2089120= 6.208 ????
Switching x,÷
: 10000+729-1728= 9001= ????
Seventh bonus (@QPaysTaxes): operator precedence applies backwards, calculator breaks on any decimal:
8+4-2
Then:
Switching +,-
: 8-4+2=2
Switching +,x
: 8x4-2=16
Switching +,÷
: 8÷4-2=8
Switching -,x
: 8+4x2=24
Switching -,÷
: 8+4÷2=6
Switching x,÷
: 8+4-2=10