add: questions and exercises for the if statement

11-if/questions/5-short-if.md

@@ -0,0 +1,71 @@
+## How to fix this program?
+```go
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func main() {
+	if err != nil; d, err := time.ParseDuration("1h10s") {
+		fmt.Println(d)
+	}
+}
+```
+1. Swap the simple statement with the `err != nil` check. *CORRECT*
+2. Remove the error handling.
+3. Remove the semicolon.
+4. Change the short declaration to an assignment.
+
+> **1:** Yes. In a short if statement, the simple statement (the short declaration there) should be the first part of it. Then, after the semicolon separator, there should be a condition expression.
+> 
+> **2:** You don't want that. That's not the issue here.
+
+
+## What does this program print?
+```go
+package main
+import "fmt"
+
+func main() {
+	done := false
+	if done := true; done {
+		fmt.Println(done)
+	}
+	fmt.Println(done)
+}
+```
+1. true and true
+2. false and false
+3. true and false *CORRECT*
+4. false and true
+
+> **3:** Yes. It shadows the main()'s done variable, and inside the if statement, it prints "true". Then, after the if statement ends, it prints the main()'s done variable which is "false".
+
+
+## How can you fix this code?
+```go
+package main
+import "fmt"
+
+func main() {
+	done := false
+	if done := true; done {
+		fmt.Println(done)
+	}
+	fmt.Println(done)
+}
+```
+1. Remove the first declaration (main()'s done)
+2. Remove the declaration in the short-if (if's done)
+3. Change the done declaration of the main() to an assignment
+4. Change the done declaration of the short-if to an assignment. And, after the if statement, assign false back to the done variable. *CORRECT*
+
+> **1:** That will break the program. The last line tries to print it.
+> 
+> **2:** The program wants to use it to print true.
+> 
+> **3:** There will be "undefined variable" error.
+> **4:** Yes, that will solve the shadowing issue. Short-if will reuse the same done variable of the main(). And, after the short-if, done will be false because of the assignment, and it will print false.
+