c++ how a char variable more than 128 output

January 19, 2023

Here is my code:

#include <bits/stdc++.h>
using namespace std;
int main(){
    char a = 129;
    printf("%d", a);
}

OUTPUT:-127
I want to konw how 129 changes to -127.

>Solution :

It is a little bit of code you have, but you can learn a lot from it already.
One is to never ignore compiler warnings 🙂

Here is some modified code to help you explain things :

// #include <bits/stdc++.h> // NO never use this it is NOT a standard header file 
// using namespace std; // NO never use using namespace std; (using namespace is not recommended at all in big projects).

#include <iostream> // for console output
#include <format>   // C++20 replacement for printf
#include <limits>   // get information on maximum and minimum values

int main() 
{
    // NEVER ignore your compiler warnings. The compiler already warns value will not fit!!!
    // \temp\main.cpp(11,14): warning C4309: 'initializing': truncation of constant value
    char a = 129; // a signed char will not hold this.
    // printf("%d", a); // printf can be used, but is considered "unsafe" (can lead to buffer overflows)

    std::cout << std::format("the value of your number {}\n", a); // C++20

    // in the following code the casts are necessary to convert from char to a size value (otherwise output will show control characters)
    std::cout << "the minimum value in a char = " << static_cast<std::size_t>(std::numeric_limits<char>::min()) << "\n"; 
    std::cout << "the maximum value in a char = " << static_cast<std::size_t>(std::numeric_limits<char>::max()) << "\n";

    std::cout << "the minimum value in an unsigned char = " << static_cast<std::size_t>(std::numeric_limits<unsigned char>::min()) << "\n";
    std::cout << "the maximum value in an unsigned char = " << static_cast<std::size_t>(std::numeric_limits<unsigned char>::max()) << "\n";

    return 0;
}

So you have a choice to make, use numbers <129 or change to unsigned char.
or std::uint8_t