Type an expression in the following box (e.g., 10.5+20*3/25).

- Only numbers and +,-,* and / operators are allowed in the expression.
- The evaluation follows the standard operator precedence.
- The calculator does not support parentheses.
- The calculator handles invalid input "gracefully". It does not output PHP error messages.

- A basic arithmetic operation: 3+4*5=23
- An expression with floating point or negative sign : -3.2+2*4-1/3 = 4.46666666667, 3+-2.1*2 = -1.2
- Some typos inside operation (e.g. alphabetic letter): Invalid input expression 2d4+1