Transform a string into a number : expr

Use expr, the parser with a string representing a number.

• For integers, enter the string representing the integer without leading 0 for basis 10, with prefix 0x for basis 16, 0 for basis 8 or 0b for basis 2. Input :
  expr("123")
  Output :
  123
  Input :
  expr("0123")
  Output :
  83
  Because : 1*8² + 2*8 + 3 = 83 Input :
  expr("0x12f")
  Output :
  303
  Because : 1*16² + 2*16 + 15 = 303
• For decimal numbers, use a string with a . or e inside.
  Input :
  expr("123.4567")
  Output :
  123.4567
  Input :
  expr("123e-5")
  Output :
  0.00123
• Note that expr more generally transforms a string into a command if the command exists.
  Input :
  expr("a:=1")
  Output :
  1
  Then, input :
  a
  Output :
  1