CSC204: Principles of Programming Languages Assignment Statements

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Questions and Answers

Which of the following languages use !== and != for inequality?

C and F#

Lua and ML

JavaScript and Lua

JavaScript and PHP (correct)

What is the operator for 'not' in C?

!not

! (correct)

Which of the following operators has the highest precedence in C-based languages?

postfix ++, -- (correct)

unary +, unary -, prefix ++, --

binary +, binary -

What is the term for an expression that is determined without evaluating all of the operands and/or operators?

Short circuit evaluation Signup and view all the answers

In which of the following languages are all logical operators short-circuit evaluated?

Ruby, Perl, ML, F#, and Python Signup and view all the answers

What is the primary role of expressions in programming languages?

To specify computations Signup and view all the answers

What is the result of the expression "7" == 7 in JavaScript?

True Signup and view all the answers

What is the primary motivation behind the development of the first programming languages?

To handle arithmetic operations Signup and view all the answers

What is the term for an operator that has one operand?

Unary operator Signup and view all the answers

What is the operator for 'and' in Perl and Ruby?

and Signup and view all the answers

What determines the order in which adjacent operators of different precedence levels are evaluated?

Operator precedence rules Signup and view all the answers

What type of operator has three operands?

Ternary operator Signup and view all the answers

What is the typical precedence level of the '*' operator?

Third highest Signup and view all the answers

What determines the order in which adjacent operators with the same precedence level are evaluated?

Operator associativity rules Signup and view all the answers

What is the essence of imperative languages?

The dominant role of assignment statements Signup and view all the answers

What is the primary difference between the assignment operator in FORTRAN, BASIC, and the C-based languages, and the assignment operator in ALGOLs, Pascal, and Ada?

The former uses = for assignment, while the latter uses := for assignment. Signup and view all the answers

What is the purpose of using == as the relational operator in the C-based languages?

To differentiate between the assignment operator and the equality operator. Signup and view all the answers

What is the equivalent of the conditional target statement ($flag ?$total : $subtotal) = 0; in Perl?

if ($flag) {$total = 0} else {$subtotal = 0} Signup and view all the answers

What is the purpose of compound assignment operators?

To provide a shorthand method of specifying a commonly needed form of assignment. Signup and view all the answers

What is the effect of the statement sum = ++count;

Count is incremented, then assigned to sum. Signup and view all the answers

What is the primary risk of using assignment as an expression in C?

Loss of error detection. Signup and view all the answers

What is the purpose of the statement ch = getchar () in the context of the while loop?

To use the result of getchar () as a conditional value. Signup and view all the answers

What is the associativity rule for the ** operator in most programming languages?

Right to left Signup and view all the answers

What is the difference between the statements sum = ++count and sum = count++?

The first statement increments count before assigning it to sum, while the second statement assigns count to sum before incrementing it. Signup and view all the answers

What is the purpose of using parentheses in an expression?

To override the precedence and associativity rules Signup and view all the answers

What is the order of evaluation for operands in an expression?

Parenthesized expressions, variables, constants Signup and view all the answers

What is a functional side effect in programming?

When a function changes a non-local variable or a two-way parameter Signup and view all the answers

What is the problem with functional side effects in programming?

They can cause unexpected behavior when a function alters another operand Signup and view all the answers

What is operator overloading in programming?

Using an operator for more than one purpose Signup and view all the answers

Which programming languages allow user-defined overloaded operators?

C++ and Ada Signup and view all the answers

What is the purpose of the ternary operator in conditional expressions?

To evaluate a conditional expression in a single line Signup and view all the answers

What is the primary concern with users defining nonsense operations in a programming language?

It may compromise the readability of the code Signup and view all the answers

What is the term for a type conversion that converts a value to a type that cannot include all of the values of the original type?

Narrowing conversion Signup and view all the answers

What is the term for an implicit type conversion in an expression?

Coercion Signup and view all the answers

What is the disadvantage of using coercions in expressions?

Compilers may not detect the coercion as a type error Signup and view all the answers

What is the term for a result of an operation that cannot be represented in the memory cell where it must be stored?

Overflow Signup and view all the answers

What is the term for the limitations of arithmetic that result in a runtime error?

Division by zero Signup and view all the answers

What is the primary purpose of relational expressions in programming?

To evaluate to a Boolean representation Signup and view all the answers

What is the term for the process of converting a value to a type that can include at least approximations of all of the values of the original type?

Widening conversion Signup and view all the answers

Study Notes

Assignment Statements

The general syntax of assignment statements varies across programming languages.
The assignment operator is = in FORTRAN, BASIC, and C-based languages, while it is := in ALGOLs, Pascal, and Ada.
Using = as both the assignment and relational operator can lead to ambiguity, which is why C-based languages use == for relational equality.

Conditional Targets

Conditional targets allow assignment statements to be executed based on a condition.
Example: ($flag ? $total : $subtotal) = 0; in Perl, which is equivalent to an if-else statement.

Compound Assignment Operators

Compound assignment operators are a shorthand for specifying a common form of assignment.
Introduced in ALGOL and adopted by C and other languages.
Example: a = a + b can be written as a += b.

Unary Assignment Operators

Unary assignment operators in C-based languages combine increment and decrement operations with assignment.
Examples: sum = ++count, sum = count++, count++, and -count++.

Assignment as an Expression

In C and C++, the assignment statement produces a result and can be used as an operand.
This can lead to loss of error detection and program errors.
Example: while ((ch = getchar ()) != EOF) {…}.

Boolean Expressions

Operands are Boolean, and the result is Boolean.
Example operators: && and || in C, and and or in Ada, and and and or in Perl and Ruby.

Short-Circuit Evaluation

An expression where the result is determined without evaluating all operands and operators.
Example: (13 * a) * (b / 13 - 1) - if a is zero, there is no need to evaluate (b / 13 - 1).
C, C++, and Java use short-circuit evaluation for Boolean operators && and ||.

Introduction

Expressions are a fundamental means of specifying computations in a programming language.
To understand expression evaluation, one needs to be familiar with the orders of operator and operand evaluation.
The essence of imperative languages is the dominant role of assignment statements.

Arithmetic Expressions

Arithmetic expressions consist of operators, operands, parentheses, and function calls.
Arithmetic operators: unary, binary, and ternary operators.

Operator Precedence Rules

The operator precedence rules define the order in which adjacent operators of different precedence levels are evaluated.
Typical precedence levels: parentheses, unary operators, **, *, /, +, and -.

Operator Associativity Rules

The operator associativity rules define the order in which adjacent operators with the same precedence level are evaluated.
Typical associativity rules: left to right, except for ** which is right to left.

Conditional Expressions

Conditional expressions: if-then-else statements in C-based languages.
Example: average = (count == 0) ? 0 : sum / count.

Operand Evaluation Order

Variables: fetch the value from memory.
Constants: sometimes a fetch from memory, sometimes the constant is in the machine language instruction.
Parenthesized expressions: evaluate all operators before evaluating the operand.

Functional Side Effects

Functional side effects: when a function changes a two-way parameter or a non-local variable.
Problems: when a function referenced in an expression alters another operand of the expression.

Overloaded Operators

Use of an operator for more than one purpose is called operator overloading.
Example: & in C++ as a binary operator for bitwise logical AND operation and as a unary operator for the address of operator.

Type Conversions

A narrowing conversion is one that converts a value to a type that cannot include all of the values of the original type.
A widening conversion converts a value to a type that can include at least approximations of all of the values of the original type.
Explicit type conversion: casting in C-based languages.

Coercion in Expressions

A mixed-mode expression is one that has operands of different types.
A coercion is an implicit type conversion.
In most languages, all numeric types are coerced in expressions, using widening conversions.

Errors in Expressions

Causes: overflow or underflow, and division by zero.
These are examples of run-time errors, which are called exceptions.

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Description

This quiz covers the general syntax of assignment statements, assignment operators, and conditional targets in programming languages.