Exercise 9

Added Exercise 9 to repository

Informatik_I/Exercise_9/Task_2/README.org

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+#+title: Task 2: Understanding struct & classes
+
+#+author: JirR02
+/This task is a text based task. You do not need to write any
+program/C++ file: the answer should be written in main.md (and might
+include code fragments if questions ask for them)./
+
+* Task
+:PROPERTIES:
+:CUSTOM_ID: task
+:END:
+Consider the following definitions:
+
+1. 
+
+#+begin_src cpp
+struct A {
+int a;
+double b;
+int c;
+};
+
+A str = {1, 1.5, 2};
+std::vector<int> vec = {1, 1, 3};
+int& a = vec[0];
+#+end_src
+
+For each of the provided expressions state their /C++ type/ and /value/:
+
+1. =str.a * str.b=
+2. =str.b == vec[1]=
+3. =str.a * str.b / str.c=
+4. =vec[str.a] / str.c=
+5. =a / 2 - str.b=
+
+2. [@2] 
+
+#+begin_src cpp
+class B {
+public:
+B(): vec(128) {
+for (int i = 0; i < 128; ++i) {
+vec[i] = 0;
+}
+}
+    
+// PRE: ...
+// POST: ...
+void add(const char c) {
+++vec[c];
+}
+    
+// PRE: ...
+// POST: ...
+int get(const char c) const {
+return vec[c];
+}
+
+private:
+std::vector<int> vec;
+};
+#+end_src
+
+Determine PRE- and POST-conditions for the methods add and get. As these
+methods are members functions of class B, PRE- and POST-conditions
+should be derived taking the public interface of the class into account.
+
+* Solution
+:PROPERTIES:
+:CUSTOM_ID: solution
+:END:
+#+begin_src markdown
+
+1. `plain|`
+
+1. Type: `cpp|double` / Value: `cpp|1.5`
+2. Type: `cpp|bool` / Value: `cpp|true`
+3. Type: `cpp|double` / Value: `cpp|0.75`
+4. Type: `cpp|int` / Value: `cpp|0`
+5. Type: `cpp|double` / Value: `cpp|-1.5`
+
+2. ```c++
+// PRE: 0 <= c < 128
+// POST: Increments the value of the vector at position c
+void add(const char c);
+
+// PRE: 0 <= c < 128
+// POST: Gets the value of the vector at position c
+int get(const char c) const;
+#+end_src
+
+```
+
+--------------
+
+Made by JirR02 in Switzerland 🇨🇭