add type-conversions/as.md

solutions/type-conversions/as.md

@@ -0,0 +1,88 @@
+1.
+```rust
+fn main() {
+    let decimal = 97.123_f32;
+
+    let integer: u8 = decimal as u8;
+
+    let c1: char = decimal as u8 as char;
+    let c2 = integer as char;
+
+    assert_eq!(integer, 'b' as u8 - 1);
+}
+```
+
+2.
+```rust
+// Suppress all warnings from casts which overflow.
+#![allow(overflowing_literals)]
+
+fn main() {
+    assert_eq!(u8::MAX, 255);
+    let v = 1000 as u8;
+}
+```
+
+3.
+```rust
+fn main() {
+    assert_eq!(1000 as u16, 1000);
+
+    assert_eq!(1000 as u8, 232);
+
+    // For positive numbers, this is the same as the modulus
+    println!("1000 mod 256 is : {}", 1000 % 256);
+
+    assert_eq!(-1_i8 as u8, 255);
+    
+    // Since Rust 1.45, the `as` keyword performs a *saturating cast* 
+    // when casting from float to int. If the floating point value exceeds 
+    // the upper bound or is less than the lower bound, the returned value 
+    // will be equal to the bound crossed.
+    assert_eq!(300.1_f32 as u8, 255);
+    assert_eq!(-100.1_f32 as u8, 0);
+    
+
+    // This behavior incurs a small runtime cost and can be avoided 
+    // with unsafe methods, however the results might overflow and 
+    // return **unsound values**. Use these methods wisely:
+    unsafe {
+        // 300.0 is 44
+        println!("300.0 is {}", 300.0_f32.to_int_unchecked::<u8>());
+        // -100.0 as u8 is 156
+        println!("-100.0 as u8 is {}", (-100.0_f32).to_int_unchecked::<u8>());
+        // nan as u8 is 0
+        println!("nan as u8 is {}", f32::NAN.to_int_unchecked::<u8>());
+    }
+}
+```
+
+4.
+```rust
+fn main() {
+    let mut values: [i32; 2] = [1, 2];
+    let p1: *mut i32 = values.as_mut_ptr();
+    let first_address = p1 as usize; 
+    let second_address = first_address + 4; // 4 == std::mem::size_of::<i32>()
+    let p2 = second_address as *mut i32;
+    unsafe {
+        *p2 += 1;
+    }
+    assert_eq!(values[1], 3);
+
+    println!("Success!")
+}
+```
+
+5.
+```rust
+fn main() {
+    let arr :[u64; 13] = [0; 13];
+    assert_eq!(std::mem::size_of_val(&arr), 8 * 13);
+    let a: *const [u64] = &arr;
+    let b = a as *const [u8];
+    unsafe {
+        assert_eq!(std::mem::size_of_val(&*b), 13)
+    }
+}
+```