add chapter [println and format]

solutions/formatted-output/println.md

@@ -0,0 +1,18 @@
+1.
+```rust
+fn main() {
+    let s1 = "hello";
+    /* Fill in the blank */
+    let s = format!("{}, world!", s1);
+    assert_eq!(s, "hello, world!");
+}
+```
+
+2.
+```rust
+fn main() {
+    print!("hello world, ");
+    println!("I am");
+    println!("Sunface!");
+}
+```

src/SUMMARY.md

@@ -45,8 +45,8 @@
   - [Advanced use and pub](crate-module/use-pub.md)
 - [Comments and Docs](comments-docs.md)
 - [Formatted output](formatted-output/intro.md)
-  - [Debug and Display](formatted-output/debug-display.md)
   - [println! and format!](formatted-output/println.md)
+  - [Debug and Display](formatted-output/debug-display.md)
   - [formating](formatted-output/formatting.md)
 - [Lifetime TODO](lifetime/intro.md)
   - [basic](lifetime/basic.md)

src/formatted-output/intro.md

@@ -1,17 +1,5 @@
 # Formatted output
 
-Printing is handled by a series of [`macros`][macros] defined in [`std::fmt`][fmt]
-some of which include:
-
-* `format!`: write formatted text to [`String`][string]
-* `print!`: same as `format!` but the text is printed to the console (io::stdout).
-* `println!`: same as `print!` but a newline is appended.
-* `eprint!`: same as `format!` but the text is printed to the standard error (io::stderr).
-* `eprintln!`: same as `eprint!`but a newline is appended.
-
-All parse text in the same fashion. As a plus, Rust checks formatting
-correctness at compile time.
-
 ```rust,editable,ignore,mdbook-runnable
 fn main() {
     // In general, the `{}` will be automatically replaced with any

src/formatted-output/println.md

@@ -1 +1,39 @@
 # println! and format!
+Printing is handled by a series of [`macros`][macros] defined in [`std::fmt`][fmt]
+some of which include:
+
+* `format!`: write formatted text to [`String`][string]
+* `print!`: same as `format!` but the text is printed to the console (io::stdout).
+* `println!`: same as `print!` but a newline is appended.
+* `eprint!`: same as `format!` but the text is printed to the standard error (io::stderr).
+* `eprintln!`: same as `eprint!`but a newline is appended.
+
+All parse text in the same fashion. As a plus, Rust checks formatting
+correctness at compile time.
+
+## `format!`
+1.🌟
+```rust,editable
+
+fn main() {
+    let s1 = "hello";
+    /* Fill in the blank */
+    let s = format!(__);
+    assert_eq!(s, "hello, world!");
+}
+```
+
+## `print!`, `println!`
+2.🌟
+```rust,editable
+
+fn main() {
+   /* Fill in the blanks to make it print:
+   Hello world, I am 
+   Sunface!
+   */
+   __("hello world, ");
+   __("I am");
+   __("Sunface!");
+}
+```