What is difference between two programs in c++?

Question

string s;
cin>>s;
cout<<(s[0])*10;

string s;
cin>>s;
cout<<(s[0]-'0')*10;

both produce different answers while input is a number
suppose if input is 2756 the first program gives 550
the second one gives 70
why?

Answer 1

i guess your input start from 7 not from 2.
lets take 7 . ascii value of 0 is 48 and ascii value of 7 is 55.
lets take fist one s[0]= 7 then ascii of 7 is 55*10=550
second one s[0】-'0'=55-48=7
7*10=70