CSC204 Chapter 7: Expressions and Statements

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Questions and Answers

What is the role of assignment statements in imperative languages?

They are used to declare variables

They are used to define functions

They play a dominant role (correct)

They are used to write comments

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

For arithmetic evaluation (correct)

To develop operating systems

To create websites

To develop games

What type of operator has three operands?

Unary operator

Ternary operator (correct)

Quaternary operator

Binary operator

What is the order in which operators are evaluated in an expression, according to the operator precedence rules?

Unary operators, parentheses, *, /, +, - Signup and view all the answers

What is the purpose of operator associativity rules?

To define the order in which adjacent operators with the same precedence level are evaluated Signup and view all the answers

What is the essential element of computations in a programming language?

Expressions Signup and view all the answers

What is composed of operators, operands, parentheses, and function calls?

Arithmetic expressions Signup and view all the answers

What is the order in which operators are evaluated in an expression, according to the operator precedence rules, if the language supports it?

Parentheses, **, *, /, +, - Signup and view all the answers

What is the inequality operator in Lua?

~= Signup and view all the answers

What is the logical AND operator in Perl?

&& Signup and view all the answers

What is the precedence of the relational operators in C-based languages?

Highest Signup and view all the answers

What is the consequence of short-circuit evaluation in a Boolean expression?

The result is determined without evaluating all operands Signup and view all the answers

Which programming languages use short-circuit evaluation for all logical operators?

Ruby, Perl, ML, F#, and Python 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 associativity rule for the ** operator in typical programming languages?

Right to left Signup and view all the answers

What is the operator for logical NOT in C?

! Signup and view all the answers

Which of the following languages use the 'and' keyword for logical AND?

Perl and Ruby Signup and view all the answers

How can the precedence and associativity rules be overridden in programming languages?

Using parentheses Signup and view all the answers

What is the purpose of the ?: operator in C-based languages?

To provide a conditional expression Signup and view all the answers

What is the order of evaluation for operands in programming languages?

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

What is an example of a functional side effect?

A function changing a non-local variable Signup and view all the answers

What is operator overloading in programming languages?

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 problem with functional side effects in programming languages?

They can cause unexpected changes to operands Signup and view all the answers

What is a disadvantage of allowing users to define their own operations?

It can lead to users defining nonsense operations. Signup and view all the answers

What is an example of a narrowing conversion?

Converting a double to a float. Signup and view all the answers

What is coercion in expressions?

An implicit type conversion. Signup and view all the answers

What happens when a mixed-mode expression is evaluated?

The expression is evaluated using widening conversions. Signup and view all the answers

What is a common cause of run-time errors in expressions?

All of the above. Signup and view all the answers

What is the result of evaluating a relational expression?

A Boolean value. Signup and view all the answers

What is an example of explicit type conversion?

float b = (int) sum; Signup and view all the answers

What is a widening conversion?

Converting an int to a float. Signup and view all the answers

What is the assignment operator used in FORTRAN, BASIC, and the C-based languages?

= Signup and view all the answers

Why do C-based languages use '==' as the relational operator?

To avoid overloading the '=' operator Signup and view all the answers

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

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

What is the purpose of compound assignment operators?

To simplify the syntax of assignment statements 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 result of the assignment statement in the expression 'while ((ch = getchar ()) != EOF){…}'?

The result is used as a conditional value Signup and view all the answers

What can be a consequence of using assignment statements as expressions?

Loss of error detection Signup and view all the answers

In which languages are unary assignment operators used to combine increment and decrement operations with assignment?

C-based languages Signup and view all the answers

Study Notes

Introduction to Expressions

Expressions are the fundamental means of specifying computations in a programming language.
Understanding expression evaluation requires familiarity with the orders of operator and operand evaluation.

Arithmetic Expressions

Arithmetic evaluation was a motivation for the development of the first programming languages.
Arithmetic expressions consist of operators, operands, parentheses, and function calls.
Types of arithmetic operators: • Unary operators: have one operand. • Binary operators: have two operands. • Ternary operators: have three operands.

Operator Precedence Rules

Operator precedence rules define the order in which "adjacent" operators of different precedence levels are evaluated.
Typical precedence levels: • Parentheses. • Unary operators. • ** (if the language supports it). • *, /. • +, -.

Operator Associativity Rules

Operator associativity rules define the order in which adjacent operators with the same precedence level are evaluated.
Typical associativity rules: • Left to right, except **, which is right to left. • Sometimes unary operators associate right to left (e.g., in FORTRAN).
Precedence and associativity rules can be overridden with parentheses.

Conditional Expressions

C-based languages (e.g., C, C++): use if-then-else statements.
Example: average = (count == 0)? 0 : sum / count.

Operand Evaluation Order

Evaluation order:
1. Variables: fetch the value from memory.
2. Constants: sometimes a fetch from memory; sometimes the constant is in the machine language instruction.
3. Parenthesized expressions: evaluate all operators before evaluating the operand.

Functional Side Effects

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

Overloaded Operators

Overloaded operators: use of an operator for more than one purpose.
Example: ‘&’ in C++ (both bitwise logical AND operation and address of operator).
Problems with overloaded operators: • Users can define nonsense operations. • Readability may suffer.

Type Conversions

Narrowing conversion: converts a value to a type that cannot include all of the values of the original type.
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: called casting in C-based languages.

Coercion in Expressions

Mixed-mode expression: has operands of different types.
Coercion: an implicit type conversion.
In most languages, all numeric types are coerced in expressions, using widening conversions.

Errors in Expressions

Causes: • Overflow or underflow. • Division by zero.
These are examples of run-time errors, which are called exceptions.

Relational Expressions

Use relational operators and operands of various types.
Evaluate to some Boolean representation.
Operator symbols used vary among languages.

Boolean Expressions

Operands are Boolean and the result is Boolean.
Example operators: • &&. • ||. • !.
Precedence of the arithmetic, relational, and Boolean operators in the C-based languages.

Short-Circuit Evaluation

Evaluates an expression without evaluating all of the operands and/or operators.
Example: (13 * a) * (b / 13 – 1).
C, C++, and Java: use short-circuit evaluation for the usual Boolean operators (&& and ||).

Assignment Statements

The general syntax: variable = expression.
The assignment operator: • = (FORTRAN, BASIC, the C-based languages). • := (ALGOLs, Pascal, Ada).
= can be bad when it is overloaded for the relational operator for equality.

Conditional Targets

Conditional targets on assignment statements (Perl).
Example: ($flag ?$total : $subtotal) = 0.

Compound Assignment Operators

A shorthand method of specifying a commonly needed form of assignment.
Introduced in ALGOL; adopted by C and other languages.
Example: 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++. • -count++.

Assignment as an Expression

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

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Description

This quiz covers the concepts of expressions and statements in programming languages, including arithmetic expressions, overloaded operators, type conversions, and assignment statements.