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1. • • The following example creates a dictionary containing the atomic masses of some chemical elements. The element names are the keys and the masses are the values. The dictionary is a set of key:value pairs: In : atomic_mass = {'H': 1., 'C': 12, 'S': 32} Then we can add another key:value entry using: In : atomic_mass ['O'] = 16.
     csc.ucdavis.edu › ~chaos › courses

     Part C: Dictionaries, Arrays, Functions, and Modules - UC Davis

2. Top results related to what are the function of dictionary keys in c programming example

   • What are the benefits of function pointers in C?

     Top Answer

     Answered Jul 19, 2017 · 3 votes

     • Same as regular typdefs, incredibly useful for 2 and 4. Instead of typing the whole thing, you can now use myFuncDef
     • A function declaration for a function that recieves a function pointer. A function that takes a function pointer of 1. would thus look int add2to3(myFuncDef functionPtr);
     • -
     • A function that takes an int and (probably based on that) returns you a function pointer. Using the typedef it would have looked like myFuncDef functionFactory(int n);

     Without typedefs these chains of pointers to pointers could get incredibly long as can be seen in this question: C syntax for functions returning function pointers

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     1/5

   • What are the semantics of function pointers with empty parentheses in each C standard?

     Top Answer

     Answered Mar 25, 2018 · 2 votes

     N1570 6.11.6:

     The use of function declarators with empty parentheses (not prototype-format parameter type declarators) is an obsolescent feature.

     This same wording appears in the 1990, 1999, and 2011 editions of the ISO C standard. There has been no change. The word obsolescent says that the feature may be removed in a future edition of the Standard, but so far the committee has not done so. (Function pointer declarations are just one of several contexts where function declarators can appear.)

     The Introduction section of the C standard explains what obsolescent means:

     Certain features are obsolescent, which means that they may be considered for withdrawal in future revisions of this International Standard. They are retained because of their widespread use, but their use in new implementations (for implementation features) or new programs (for language [6.11] or library features [7.31]) is discouraged.

     A call to a function declared with an old-style declarator is still required to pass the correct number and type(s) of arguments (after promotion) as defined by the function's actual definition. A call with incorrect arguments has undefined behavior, which means that the compiler is not required to diagnose the error; the burden is entirely on the programmer.

     This is why prototypes were introduced, so that the compiler could check correctness of arguments.

     On an i386 system with GCC, “extra” arguments passed in a call to an empty-parentheses-type’d function pointer are ignored, because of how stack frames work ...

     Yes, that's well within the bounds of undefined behavior. The worst symptom of undefined behavior is having the program work exactly as you expect it to. It means that you have a bug that hasn't exhibited itself yet, and it will be difficult to track it down.

     You should not depend on that unless you have a very good reason to do so.

     If you change

     int (*fp)() = foo;-

     to

     int (*fp)(int) = foo;-

     the compiler will diagnose the incorrect call.

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     2/5

   • What are the different between calling constructor and calling function pointer of constructor in C++

     Top Answer

     Answered Jan 28, 2024 · 0 votes

     Calling a constructor and calling a function pointer of a constructor in C++ are very similar in the sense that they are both quite impossible:

     • You cannot call a constructor in C++.
     • You cannot obtain a pointer to a constructor in C++.

     According to the C++ spec about constructors:

     Constructors have no names and cannot be called directly.

     So, in C++, you do not call constructors. The language does that for you when you use the new keyword, when you declare an object on the stack, etc. The expression new MyClass() might look like a constructor invocation, and it does in fact contain a constructor invocation, and so it might be mistaken for a constructor invocation, but that's not what it is; it is a "new expression", which includes, among other things, an invocation of a constructor. But the other things are crucial: you cannot just skip them and directly invoke the constructor.

     Function pointers of constructors do not exist because normally you cannot take the address of a constructor. If you examine the names exported by the DLL, and somehow figure out which name corresponds to the constructor, and use that name to obtain the entry point of that constructor from the DLL, you are cheating: you are doing something which is not normally supported by the language. As a result, you should not attempt to invoke that entry point. A constructor is only supposed to be invoked by the language.

     Also according to the C++ spec:

     A constructor is a special non-static member function of a class.

     (Emphasis mine.)

     A constructor assumes that memory has been allocated, and proceeds to initialize that memory. The language takes care of the memory allocation, but invoking the constructor directly does not. Since a constructor is non-static, it expects an uninitialized this to be passed to it, but you are not allocating any memory and you are not passing anything to the constructor. The result is exactly as expected: a crash.

     And besides, think about it: the constructor could not be internally allocating the memory, because how would it work then if the object was allocated on the stack? And how would it work if the constructor was being invoked by the constructor of a derived class which presumably occupies more memory?

     You can get your DLL to work by using a factory method. A factory method is a public static method which executes new ClassA() and returns the result, or declares ClassA() and returns it by value. Then, obtain the address of the factory method from the DLL, and invoke it.

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     3/5

   • What are the things that are allowed as keys in a python dictionary?

     Top Answer

     Answered Jul 21, 2018 · 1 votes

     A key must be immutable.

     That is the only limitations.For example, You can use a tuple as the key if the items within tuple are immutable : (1,2)

     But you can not do this ([1,2])

     Read up more about immutable and mutable types to get a clear idea.

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     4/5

   • What are the differences between pointer variable's value & address of normal variable and what are the special purpose of pointers in C?

     Top Answer

     Answered Jun 26, 2017 · 5 votes

     Answering questions in reverse order:

     C does not have array variables....but this is really just working with pointers with an alternative syntax.

     This is incorrect, and you need to toss that bookmark in the trash. It's a common misconception that arrays and pointers are the same thing, but they are not. An array expression will be converted to a pointer expression under most circumstances, and array subscripting is accomplished through pointer arithmetic, but an array object is an actual array, not a pointer.

     If pointer also keeps the variable's address in it and at the same time we can get the variable's address using & sign, can't we do the same task pointer does by deriving the address of any variable? I mean if I don't declare it as pointer and use it as int ptr = &i; in 2nd code snippet and use it as normal variable, what would be the differences?

     That code doesn't illustrate why pointers exist, or why they are useful.

     C actually requires us to use pointers in the following cases:

     • To write to a function's parameters;
     • To track dynamically allocated memory;

     Pointers also make dynamic data structures like trees and lists easy to implement, but they aren't required for it (unless you're using dynamic memory allocation in those structures).

     Writing to a function's parameters

     C passes all function arguments by value; the formal parameter in the function definition is a separate object in memory from the actual parameter in the function call, so any change to the formal parameter is not reflected in the actual parameter. For example, assume the following swap function:

     void swap( int a, int b ) { int t = a; a = b; b = t; }-

     This function exchanges the values in a and b. However, when we call the function as

     int x = 4, y = 5;swap( x, y );-

     the values of x and y won't be updated, because they are different objects than a and b. If we want to update x and y, we have to pass pointers to them:

     swap( &x, &y );-

     and update the function definition as follows:

     void swap( int *a, int *b ) { int t = *a; *a = *b; *b = t; }-

     Instead of swapping the contents of a and b, we swap the contents of the objects that a and b point to. This crops up all the time - think about the scanf function, and how you have to use the & operator on scalar arguments.

     Tracking dynamically allocated memory

     The dynamic memory allocation functions malloc, calloc, and realloc all return pointers to dynamic memory buffers; there's no variable associated with that memory as such.

     char *buffer = malloc( sizeof *buffer * some_length );-

     A pointer is the only way to track that memory.

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     5/5

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4. www.geeksforgeeks.org › implementation-on-map-orImplementation on Map or Dictionary Data Structure in C

   www.geeksforgeeks.org › implementation-on-map-or

   • Cached

   Mar 27, 2023 · Functions used to implement Map in C. The getIndex function searches for a key in the keys array and returns its index if found, or -1 if not found. The insert function inserts a key-value pair into the map. If the key already exists, it updates the value. The get function returns the value of a key in the map, or -1 if the key is not found.

5. stackoverflow.com › questions › 75846950Dictionary Implementation in C with using arrays

   stackoverflow.com › questions › 75846950

   • Cached

   Mar 26, 2023 · C programming language does not provide any direct implementation of Map or Dictionary Data structure. However, it doesn't mean we cannot implement one. In C, a simple way to implement a map is to use arrays and store the key-value pairs as elements of the array.

6. www.freecodecamp.org › news › how-to-use-functions-in-cHow to Use Functions in C - Explained With Examples

   www.freecodecamp.org › news › how-to-use-functions-in-c

   • Cached

   • What Is A Function in C?
   • How to Declare A Function in C
   • What Happens If You Call A Function Before Its Declaration in C?
   • How to Define A Function in C
   • Where Should A Function Be defined?
   • How to Pass Parameters to A Function
   • Conclusion

   A function is a block of code that executes a particular task in programing. It is a standalone piece of code that can be called from anywhere in the program. A function can take in parameters, run computations, and output a value. A function in C can be created using this syntax: The return_type specifies the type of value that the function will r...

   See full list on freecodecamp.org

   Declaring a function in C informs the compiler about the presence of a function without giving implementation details. This enables the function to be called by other sections of the software before it is specified or implemented. A function declaration usually contains the function name, return type, and the parameter types. The following is the s...

   See full list on freecodecamp.org

   In this instance, the computer believes the usual return type is an integer. If the function gives a different data type, it throws an error. If the return type is also an integer, it will function properly. But some cautions may be generated: In this code, the function function()is called before it is declared. This returns an error:

   See full list on freecodecamp.org

   Assuming you want to create a code that accepts two integers and returns their sum, you can define a function that does that this way: In this example, the function sum takes in two integer parameters – num1 and num2. The function calculates their sum and returns the result. The return type of the function is int.

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   In C, a function can be defined anywhere in the program, as long as it is defined before it is used. But it is a good practice to define functions at the beginning of the file or in a separate file to make the code more readable and organized. Here's an example code showing how to define a function in C: In this example, the function add()is define...

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   There are two methods of passing parameters (also called arguments) to a function in C: by value and by reference. When we pass a parameter by value, the method receives a copy of the parameter's value. Changes to the parameter within the code have no effect on the initial variable outside the function. When we pass a parameter by reference, the me...

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   In conclusion, functions are an essential component of C programming. You can use them to divide large problems into smaller, more manageable pieces of code. You can declare and define functions in C, and pass parameters either by value or by reference. It's a good practice to declare all functions before using them, and to define them at the begin...

   See full list on freecodecamp.org

7. csc.ucdavis.edu › ~chaos › coursesPart C: Dictionaries, Arrays, Functions, and Modules - UC Davis

   csc.ucdavis.edu › ~chaos › courses

   • Cached

   A dictionary's values, though, can be arbitrary objects. The following example creates a dictionary containing the atomic masses of some chemical elements. The element names are the keys and the masses are the values. The dictionary is a set of key:value pairs: In [1]: atomic_mass = {'H': 1., 'C': 12, 'S': 32}

8. www.geeksforgeeks.org › c-functionsC Functions - GeeksforGeeks

   www.geeksforgeeks.org › c-functions

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   Sep 5, 2023 · A function in C is a set of statements that when called perform some specific task. It is the basic building block of a C program that provides modularity and code reusability. The programming statements of a function are enclosed within { } braces, having certain meanings and performing certain operations. They are also called subroutines or ...

9. beginnersbook.com › 2014 › 01Functions in C Programming with examples - BeginnersBook

   beginnersbook.com › 2014 › 01

   • Cached

   Jun 29, 2020 · In this tutorial, we will learn functions in C programming. A function is a block of statements that performs a specific task. Let’s say you are writing a C program and you need to perform a same task in that program more than once.

10. www.makeuseof.com › c-functions-introductionAn Introduction to C Functions - MUO

    www.makeuseof.com › c-functions-introduction

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    Aug 26, 2023 · In C programming, a function is a named section of code that does something when you ask it to. It helps keep your code organized and lets you use the same action multiple times without repeating yourself. The simplest example is one you’ve already been using: the main () function.