Grades converter (char to num)

[shorodilov]

Ask for a student's score (as string) and convert it to its numeric value. Print the result.

Conversion table:

Char score	Num score	Char score	Num score
A+	5.0	C+	2.3
A	4.0	C	2.0
A-	3.7	C-	1.7
B+	3.3	D+	1.3
B	3.0	D	1.0
B-	2.7	F	0