Convert string to int. x86 32 bit Assembler using Nasm

Question

So I\'m trying to convert a string to a number so I can add another number to it later. here is what I have to far in my .text for the conversion. num2Entered is what the us

Answer 1

"123"
 |||     val = 0
 |||______ val = val + ('3' - 48) * 10power0       [val now is 3]
 ||_______ val = 3   + ('2' - 48) * 10power1       [val now is 23] 
 |________ val = 23  + ('1' - 48) * 10power2       [val now is 123]

note: ascii of '1' means 49, '2' means 50 and so on