error assign_in_control assignment in control structure

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Control Structures in Programming Languages

Control Structures are just a way to specify flow of control in programs. Any algorithm or program can be more clear and understood if they use self-contained modules called as logic or control structures. It basically analyzes and chooses in which direction a program flows based on certain parameters or conditions. There are three basic types of logic, or flow of control, known as:

• Sequence logic, or sequential flow
• Selection logic, or conditional flow
• Iteration logic, or repetitive flow

Let us see them in detail:

Sequential logic as the name suggests follows a serial or sequential flow in which the flow depends on the series of instructions given to the computer. Unless new instructions are given, the modules are executed in the obvious sequence. The sequences may be given, by means of numbered steps explicitly. Also, implicitly follows the order in which modules are written. Most of the processing, even some complex problems, will generally follow this elementary flow pattern.

Sequential Control flow

Selection Logic simply involves a number of conditions or parameters which decides one out of several written modules. The structures which use these type of logic are known as Conditional Structures . These structures can be of three types:

Implementation:

• C/C++ if statement with Examples
• Java if statement with Examples
• C/C++ if-else statement with Examples
• Java if-else statement with Examples
• C/C++ if-else if statement with Examples
• Java if-else if statement with Examples

In this way, the flow of the program depends on the set of conditions that are written. This can be more understood by the following flow charts:

Double Alternative Control Flow

Here, A is the initial value, N is the end value and I is the increment. The loop ends when A>B. K increases or decreases according to the positive and negative value of I respectively.

Repeat-For Flow

• C/C++ for loop with Examples
• Java for loop with Examples

Repeat While Flow

• C/C++ while loop with Examples
• Java while loop with Examples

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• The Book of C (version 2022.08) »
• 4. Control Structures

4. Control Structures ¶

In this chapter, we encounter the set of "control" structures in C, such as conditional statements and looping constructs. As a preview, the control structures in C are nearly identical to those found in Java (since Java syntax is heavily based on C), and bear strong resemblance to control structures found in other programming languages.

4.1. if Statement ¶

Both an if and an if-else are available in C. The <expression> can be any valid C expression. The parentheses around the expression are required, even if it is just a single variable:

You should always use curly braces around the statement block associated with an if statement. Although C allows a programmer not to include the curly braces in the case of if statements and other control structures when there is only a single statement in the statement block, you should always use the curly braces . Why, you ask, should I type those additional characters? Just ask the unfortunate engineering group at Apple that introduced the "goto fail" bug into their SSL (secure sockets layer) library: a bug that affected the macOS and iOS operating systems quite severely [ 1 ] . The upshot of this security failure is that it could have been prevented with the rigorous use of curly braces for all statement blocks.

So, for the simple form of the if statement shown above, you should really write:

As in Java, the else keyword can be used to provide alternative execution for a conditional expression. Also similar to Java, multiple if ... else if statements can be chained together. There is no elif as in Python (or elsif as in Ruby).

4.2. The conditional expression (ternary operator) ¶

The conditional expression can be used as a shorthand for some if-else statements. The general syntax of the conditional operator is:

This is an expression , not a statement , so it represents a value. The operator works by evaluating expression1 . If it is true (non-zero), it evaluates and returns expression2 . Otherwise, it evaluates and returns expression3 .

The classic example of the ternary operator is to return the smaller of two variables. Instead of writing:

you can write:

The ternary operator is viewed by some programmers as "excessively tricky" since expressions with such operators can be hard to read. Use your best judgment, and don't do something this [Horrific] example.

4.3. switch statement ¶

The switch statement is a sort of specialized form of if with the goal of efficiently separating different blocks of code based on the value of an integer. The switch expression is evaluated, and then the flow of control jumps to the matching const-expression case . The case expressions are typically int or char constants (unfortunately, you cannot use strings as case expressions). The switch statement is probably the single most syntactically awkward and error-prone feature of the C language:

Each constant needs its own case keyword and a trailing colon (:). Once execution has jumped to a particular case, the program will keep running through all the cases from that point down --- this so called fall through operation is used in the above example so that expression-3 and expression-4 run the same statements. The explicit break statements are necessary to exit the switch . Omitting the break statements is a common error --- it compiles, but leads to inadvertent, unexpected, and likely erroneous fall-through behavior.

Why does the switch statement fall-through behavior work the way it does? The best explanation might be that C was originally developed for an audience of assembly language programmers. The assembly language programmers were used to the idea of a "jump table" with fall-through behavior, so that's the way C does it (it's also relatively easy to implement it this way). Unfortunately, the audience for C is now quite different, and the fall-through behavior is widely regarded as an unfortunate part of the language.

4.4. while loop ¶

The while loop evaluates the test expression before every loop, so it can execute zero times if the condition is initially false. The conditional expression requires parentheses like the if:

Although the curly braces are not technically required if there is only one statement in the body of the while loop, you should always use the curly braces. Again, see [ 1 ] for why.

4.5. do-while loop ¶

Like a while loop, but with the test condition at the bottom of the loop. The loop body will always execute at least once. The do-while tends to be an unpopular area of the language. Although many users of C use the straight while if possible, a do-while loop can be very useful in some situations:

4.6. for loop ¶

The for loop in C contains three components that are often used in looping constructs, making it a fairly convenient statement to use. The three parts are an initializer, a continuation condition, and an action, as in:

The initializer is executed once before the body of the loop is entered. The loop continues to run as long as the continuation condition remains true. After every execution of the loop, the action is executed. The following example executes 10 times by counting 0..9. Many loops look very much like the following:

C programs often have series of the form 0..(some_number-1). It's idiomatic in C for loops like the example above to start at 0 and use < in the test so the series runs up to but not equal to the upper bound. In other languages you might start at 1 and use <= in the test.

Each of the three parts of the for loop can be made up of multiple expressions separated by commas. Expressions separated by commas are executed in order, left to right, and represent the value of the last expression.

Note that in the C standard prior to C99, it was illegal to declare a variable in the initializer part of a for loop. In C99, however, it is perfectly legal. If you compile the above code using gcc without the -std=c99 flag, you will get the following error:

Once the -std=c99 flag is added, the code compiles correctly, as expected.

4.6.1. break ¶

The break statement causes execution to exit the current loop or switch statement. Stylistically speaking, break has the potential to be a bit vulgar. It is preferable to use a straight while with a single conditional expression at the top if possible, but sometimes you are forced to use a break because the test can occur only somewhere in the midst of the statements in the loop body. To keep the code readable, be sure to make the break obvious --- forgetting to account for the action of a break is a traditional source of bugs in loop behavior:

The break does not work with if ; it only works in loops and switches. Thinking that a break refers to an if when it really refers to the enclosing while has created some high-quality bugs. When using a break , it is nice to write the enclosing loop to iterate in the most straightforward, obvious, normal way, and then use the break to explicitly catch the exceptional, weird cases.

4.6.2. continue ¶

The continue statement causes control to jump to the bottom of the loop, effectively skipping over any code below the continue . As with break , this has a reputation as being vulgar, so use it sparingly. You can almost always get the effect more clearly using an if inside your loop:

4.6.3. Statement labels and goto ¶

Continuing the theme of statements that have a tendency of being a bit vulgar, we come to the king of vulgarity, the infamous goto statement [Goto] . The structure of a goto statement in C is to unconditionally jump to a statement label, and continue execution from there. The basic structure is:

The goto statement is not uncommon to encounter in operating systems code when there is a legitimate need to handle complex errors that can happen. A pattern that you might see is something like:

Notice the structure above: there are multiple steps being performed to carry out some initialization for an operation [ 2 ] . If one of those initialization operations fails, code execution transfers to a statement to handle deinitialization , and those de-init operations happen in reverse order of initialization . It is possible to rewrite the above code to use if / else structures, but the structure becomes much more complex (see an exercise below). Although goto has the reputation of leading to "spaghetti code", judicious use of this statement in situations like the above makes for cleaner and clearer code.

Rewrite the goto example code above (the last code example, above) to use if / else instead. Which code do you think exhibits a more clear structure?

Consider the following program snippet:

What is printed if the number 3 is entered?

Say that you want to write a program that repeatedly asks for a snowfall amount, and that you want to keep asking for another value until the sum of all values exceeds a certain value. What control structure would work best to facilitate entry of the snowfall values, and why?

Say you want to write a program that computes the average of quiz scores. You have a big stack of quizzes, so you do not know the number of quizzes up front. What control structure would work best to facilitate entry of the scores, and why?

Say that you want to simulate rolling a die (singular of dice) a fixed number of times and to compute and print the average value for the die rolls. What control structure would work best for this problem, and why?

http://thedailywtf.com/articles/One-Bad-Ternary-Operator-Deserves-Another

Dijkstra. Letters to the editor: go to statement considered harmful. Communications of the ACM, Volume 11, Issue 3, March 1968. https://dl.acm.org/citation.cfm?id=362947

Table of Contents

• 4.1. if Statement
• 4.2. The conditional expression (ternary operator)
• 4.3. switch statement
• 4.4. while loop
• 4.5. do-while loop
• 4.6.1. break
• 4.6.2. continue
• 4.6.3. Statement labels and goto

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5. Arrays and Strings

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Assignment and Control

Cite this chapter.

• Peter Grogono 2  

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Programs may exhibit complex behavior even though they are built from simple components. The complexity arises from the interdependence of computations and data in the program. Obviously, the computations determine the results produced. Less obviously, but equally important, the result produced by each computation may affect a future computation. Managing the interdependence of computations and data is one of the major tasks of programming. Assignments and control structures are essential tools that help us to perform this task. Assignments give new values to variables. Control structures use results to control the order in which computations are performed.

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Grogono, P. (1995). Assignment and Control. In: Programming with Turing and Object Oriented Turing. Springer, New York, NY. https://doi.org/10.1007/978-1-4612-4238-3_2

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• Control Structures

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Scala has the control structures you find in other programming languages, and also has powerful for expressions and match expressions:

for loops and expressions

Match expressions, while loops.

• try / catch

These structures are demonstrated in the following examples.

Scala’s if / else control structure looks similar to other languages.

Note that this really is an expression —not a statement . This means that it returns a value, so you can assign the result to a variable:

As you’ll see throughout this book, all Scala control structures can be used as expressions.

An expression returns a result, while a statement does not. Statements are typically used for their side-effects, such as using println to print to the console.

The for keyword is used to create a for loop. This example shows how to print every element in a List :

The code i <- ints is referred to as a generator . In any generator p <- e , the expression e can generate zero or many bindings to the pattern p . The code that follows the closing parentheses of the generator is the body of the loop.

The code i <- ints is referred to as a generator , and the code that follows the do keyword is the body of the loop.

You can also use one or more if expressions inside a for loop. These are referred to as guards . This example prints all of the numbers in ints that are greater than 2 :

You can use multiple generators and guards. This loop iterates over the numbers 1 to 3 , and for each number it also iterates over the characters a to c . However, it also has two guards, so the only time the print statement is called is when i has the value 2 and j is the character b :

for expressions

The for keyword has even more power: When you use the yield keyword instead of do , you create for expressions which are used to calculate and yield results.

A few examples demonstrate this. Using the same ints list as the previous example, this code creates a new list, where the value of each element in the new list is twice the value of the elements in the original list:

Scala’s control structure syntax is flexible, and that for expression can be written in several other ways, depending on your preference:

This example shows how to capitalize the first character in each string in the list:

Finally, this for expression iterates over a list of strings, and returns the length of each string, but only if that length is greater than 4 :

for loops and expressions are covered in more detail in the Control Structures sections of this book, and in the Reference documentation .

Scala has a match expression, which in its most basic use is like a Java switch statement:

However, match really is an expression, meaning that it returns a result based on the pattern match, which you can bind to a variable:

match isn’t limited to working with just integer values, it can be used with any data type:

In fact, a match expression can be used to test a variable against many different types of patterns. This example shows (a) how to use a match expression as the body of a method, and (b) how to match all the different types shown:

Because the method getClassAsString takes a parameter value of type Any , it can be decomposed by any kind of pattern.

The method getClassAsString takes as a parameter a value of type Matchable , which can be any type supporting pattern matching (some types don’t support pattern matching because this could break encapsulation).

There’s much more to pattern matching in Scala. Patterns can be nested, results of patterns can be bound, and pattern matching can even be user-defined. See the pattern matching examples in the Control Structures chapter for more details.

try / catch / finally

Scala’s try / catch / finally control structure lets you catch exceptions. It’s similar to Java, but its syntax is consistent with match expressions:

Scala also has a while loop construct. Its one-line syntax looks like this:

Scala 3 still supports the Scala 2 syntax for the sake of compatibility.

The while loop multiline syntax looks like this:

Custom control structures

Thanks to features like by-name parameters, infix notation, fluent interfaces, optional parentheses, extension methods, and higher-order functions, you can also create your own code that works just like a control structure. You’ll learn more about this in the Control Structures section.

Contributors to this page:

• Introduction
• Scala Features
• Why Scala 3?
• A Taste of Scala
• Hello, World!
• Variables and Data Types
• Domain Modeling
• First-Class Functions
• Singleton Objects
• Collections
• Contextual Abstractions
• Toplevel Definitions
• A First Look at Types
• String Interpolation
• OOP Modeling
• FP Modeling
• Method Features
• Main Methods in Scala 3
• Anonymous Functions
• Function Variables
• Eta-Expansion
• Higher-Order Functions
• Write Your Own map Method
• Creating a Method That Returns a Function
• Packaging and Imports
• Scala Collections
• Collections Types
• Collections Methods
• Functional Programming
• What is Functional Programming?
• Immutable Values
• Pure Functions
• Functions Are Values
• Functional Error Handling
• Types and the Type System
• Inferred Types
• Intersection Types
• Union Types
• Algebraic Data Types
• Opaque Types
• Structural Types
• Dependent Function Types
• Other Types
• Extension Methods
• Context Parameters
• Context Bounds
• Given Imports
• Type Classes
• Multiversal Equality
• Implicit Conversions
• Concurrency
• Scala Tools
• Building and Testing Scala Projects with sbt
• Interacting with Java
• Scala for Java Developers
• Scala for JavaScript Developers
• Scala for Python Developers
• Where To Go Next

Next: Unions , Previous: Overlaying Structures , Up: Structures   [ Contents ][ Index ]

15.13 Structure Assignment

Assignment operating on a structure type copies the structure. The left and right operands must have the same type. Here is an example:

Notionally, assignment on a structure type works by copying each of the fields. Thus, if any of the fields has the const qualifier, that structure type does not allow assignment:

See Assignment Expressions .

When a structure type has a field which is an array, as here,

structure assigment such as r1 = r2 copies array fields’ contents just as it copies all the other fields.

This is the only way in C that you can operate on the whole contents of a array with one operation: when the array is contained in a struct . You can’t copy the contents of the data field as an array, because

would convert the array objects (as always) to pointers to the zeroth elements of the arrays (of type struct record * ), and the assignment would be invalid because the left operand is not an lvalue.

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error Structure assignment to non-structure object

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incompatible types when assigning to type struct * from struct

I can't understand why i get this error : The error is : "incompatible types when assigning to type 'PERSOANA * {aka struct *}' from type 'PERSOANA {aka struct }' " Can you please explain me where is the mistake ?

• dynamic-memory-allocation

• 1 You try to return a pointer to a struct when you declared to return a struct. –  Osiris Commented Jan 8, 2019 at 19:52
• 3 PERSON *read_array(int n) should be the correct syntax. –  Osiris Commented Jan 8, 2019 at 19:53
• 2 Please quote the error message in full and verbatim. It is unlikely that what you quoted is actually the exact and full message. –  Yunnosch Commented Jan 8, 2019 at 19:57
• Now it works, thx a lot mate !:) –  ballow Commented Jan 8, 2019 at 20:01
• type of v is PERSON* and return type of the function prototype is PERSON. –  Stef1611 Commented Jan 8, 2019 at 20:01

2 Answers 2

Return a pointer to PERSON , not the object PERSON .

I can't understand why i get this error : Incompatible types when assigning to type PERSON from type PERSON.

I am reasonably confident that you do not get that error, but if you actually do then you should switch to a better compiler. I speculate that the error you get is instead

, because that's in fact what you are trying to do, given your declaration of function read_array() .

From implementation and use, it appears that you want that function to return a pointer to a structure rather than a copy of the structure. That would be

... and the same in the function definition.

• Sorry for the misunderstanding, i redited my question, that's the error i've got :) Thanks a lot –  ballow Commented Jan 8, 2019 at 20:08

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