i have a quick question

```
A = 10
B = 11
C = 12
D = 13

```

I have an char array 
"5623ADCB"

I would want to find the biggest value which is D = 13 but the program doesn't recognize D = 13 when i use a for loop to look for the biggest number. Instead it outputs the D's ascii value, how do i make ensure that everytime a D is encountered, it would be recognized as 13 and not it's ascii value?

Thanks guys for your help