Question

Why does this simple C program print -2147483648?

#include <stdio.h>

int main(){
    printf("%i", (int)2147483648);
    return 0;
}

Of course if I don’t cast it and use %lld as the format specifier I get the expected output.

Answer 1

When converting an integer to a smaller signed type, the behavior is implementation-defined if the value cannot be represented in the new type:

6.3.1.3

When a value with integer type is converted to another integer type
other than _Bool, if the value can be represented by the new type, it
is unchanged.

[…]

Otherwise, the new type is signed and the value cannot be represented
in it; either the result is implementation-defined or an
implementation-defined signal is raised.