#[allow(ctypes)];
#[no_std];
#[feature(asm)];
//#[no_core];
#[feature(macro_rules)];


mod core;
pub mod stdio;
pub mod idt;


#[no_mangle]
pub unsafe fn main() {
    idt::idt_install();
    stdio::clear_screen(stdio::Green);
    stdio::write("Hello!aaa", 2, 3);
    let mut i: u32 = 0;
    let mut c: u8 = 65; // 'A'
    let N: u32 = 80000000;
    while true {
        i += 1;
        if (i % N == 0) {
            c += 1;
            stdio::putchar(2, 4, c);
        }
    }
}


#[allow(ctypes)];
#[no_std];
#[feature(asm)];
//#[no_core];
#[feature(macro_rules)];


mod core;
pub mod stdio;
pub mod idt;


#[no_mangle]
pub unsafe fn main() {
    idt::idt_install();
    stdio::clear_screen(stdio::Green);
    stdio::write("Hello!aaa", 2, 3);
    let mut i: u32 = 0;
    let N: u32 = 80000000;
    while true {
        i += 1;
        if (i % N == 0) {
            stdio::putchar(2, 4, 65 + ((i / N) as u8));
        }
    }
}


--- 
+++ 
@@ -16,11 +16,13 @@
     stdio::clear_screen(stdio::Green);
     stdio::write("Hello!aaa", 2, 3);
     let mut i: u32 = 0;
+    let mut c: u8 = 65; // 'A'
     let N: u32 = 80000000;
     while true {
         i += 1;
         if (i % N == 0) {
-            stdio::putchar(2, 4, 65 + ((i / N) as u8));
+            c += 1;
+            stdio::putchar(2, 4, c);
         }
     }
 }
Make character-printing loop more readable
