Unexpected binary output

Question

I'm writing a code to add the first and last integer of a number. But the output results in binary instead of integer. //Code

#include <iostream>
#include <string>
using namespace std;

int main() {
    int t, n;
    cin >> t;
    for (int i = 0; i < t; i++) {
        cin>> n;
        string s = to_string(n);
        char first = s[0];
        char last = s[s.length() - 1];
        int a = first;
        int b = last;
        cout << first + last;
    }
    return 0;
}

output code

/tmp/ujHkZRfwZL.o
1
1234
101

Read about the ASCII representation. For example, the character '9' has a decimal value of 57, not 9 like you might expect. — 0x5453
– 0x5453, Commented May 3, 2021 at 19:25
But the output results in binary instead of integer; Please provide the output — A. Gille
– A. Gille, Commented May 3, 2021 at 19:26
If the input is 1234 then your program, as shown, would do '1' + '4' which with ASCII will be 49 + 51 which indeed is 101. Not binary, you just haven't tested with anything else. Try e.g. 12345 instead, and the result will be 102. — Some programmer dude
– Some programmer dude, Commented May 3, 2021 at 19:33

Vlad from Moscow · Accepted Answer · 2021-05-03 19:32:08Z

2

You should at least write

    int a = first - '0';
    int b = last - '0';
    cout << a + b;

answered May 3, 2021 at 19:32

Vlad from Moscow

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4 Comments

Some programmer dude Over a year ago

It should be noted that this subtraction "trick" is only guaranteed to work with digit characters, as it's specified in the C++ specification. There are other encodings than ASCII still in active use, where it's not possible to do this on letter characters.

Aman Rawat Over a year ago

thankyou that i worked i was adding first and last instead of a and b. thankyou soo much

Aman Rawat Over a year ago

can you explain me the use of - '0' in this line why we used it

Vlad from Moscow Over a year ago

@AmnRwt If for example the object last contains the character '4' then '4' - '0' results in integer 4. Characters that correspond to digits are follow each other.

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