Lab 3: Operations and Expressions


The exercise for this lab involves a series of experiments, each investigating a different aspect of C++ expressions.

Definition: An expression is a sequence of one or more operands and zero or more operators that, when combined, produce a value.

The operands are objects; the operators are actions. Here is a simple example:

This is an expression that has one operand (the object 12), but there are no operators; and it produces a value (the object 12).

Here's a more familiar example:

    2 + 3
This too fits the definition of an expression, since it consists of two operands (the objects 2 and 3) and one operator (+) that combine to produce a value (the object 5).

Operands need not be constants:

    2.5 * x - 1.0
This also fits the definition of an expression, since it consists of three operands (the objects 2.5, x, and 1.0) and two operators (*, -) that combine to produce a value (1 less than the product of 2.5 and x).

These examples have been arithmetic expressions, expressions whose operators are familiar arithmetic operations applied to numbers. C++ provides a rich set of arithmetic operators, but since C++ has other types of data (e.g., characters and strings), we can also write expressions for other types of data.

There are other language features that determine which and when expressions are evaluated, but it basically the expressions that do all the real work. Thus, to extend our learning how to write programs, we begin with the basic building blocks — expressions.

Expressions and Statements

Expressions are the building blocks that we use to write statements. When we append a semicolon to an expression, it becomes a statement. As an example, consider the expression 2 + 3 again. If we append a semicolon,

2 + 3;
it becomes a statement. But what does the compiler do with this statement? It is instructed to "add 2 and 3", but what is it supposed to do with the result? Print it? Add it to a database? Do further computations with it? There are hundreds of possiblilities. The compiler can not guess which one to do; we must tell it. If we want to output it
    cout << 2 + 3;
or store its value in another variable
    int result = 2 + 3;
we have to specify these actions explicitly: "Send the sum of 2 and 3 to the screen (i.e., cout)." or " Save the sum of 2 and 3 in result so that it can be used later.". These are complete instructions that produce concrete results.

Some expressions are complete in themselves. In fact, the output statement above is actually an output expression that contains an arithmetic expression. Output expressions are complete in themselves, so we can just tack on a semicolon to make it a statement. (The same is true of input expressions.)


The file experiment.cpp is our "playground" for the experiments in this lab exercise. Here is a listing of it:
/* experiment.cpp is a program to conduct experiments with 
   C++ expressions.


#include <iostream>
using namespace std;

int main ()
  int i = 3, j = 5;

  cout << "i is " << i << "\n"
       << "j is " << j << "\n"
       << "i+j is " << i + j << "\n";

Download/copy this file into whatever directory/folder/project you are using for lab 3.

As indicated in the opening documentation, add the opening documentation that you are expected (by your instructor) to have there; for example,

Written by:  John Doe for CPSC 104X on Dec. 5, 2012

     Input:  Various data items required in this lab exercise
     Output: Results produced by the various experiments.

The Experiments

You may find the variable declarations that you wrote for Lab #2 useful for some of the experiments in this lab.

Experiment #1: Output Expressions

Experiment #2: Input Expressions

Experiment #3: Arithmetic Expressions

Experiment #4: Relational Expressions

Experiment #5: Logical Expressions

Experiment #6: Operator Precedence

Experiment #7: Operator Associativity

Experiment #8: Expressions Containing Functions

Experiment #9: Assignment Statements

Experiment #10: Assignment Shortcuts


Submit your answers to the questions for the experiments that you completed. Your instructor may also ask you to submit a copy or multiple copies of your program.

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Report errors to Larry Nyhoff (