PIC10A midterms

code

Precise, logical instructions given to a computer to solve a task

Entry Point

The int main() function where every C++ program starts execution

Header Files

Libraries that provide "toolboxes" of features.

#include <iostream>

Required for input and output

#include <string>

Required for advanced string manipulation

Namespace (std)

A label that prevents name conflicts. Using using namespace std; allows you to write cout instead of the full std::cout

Semicolon (;)

Used to end an instruction, similar to a period in a sentence

Curly Braces ({})

Define Scope, grouping multiple statements into a single unit

Comments

Notes ignored by the compiler. Use // for single lines or /* ... */ for blocks

Variable

A named storage location in memory.

• Declaration: Specifying a type and name (e.g., int coins;).

• Assignment: Using the = operator to store a value (e.g., coins = 5;).

• Initialization: The first time a value is assigned; it is "strongly suggested" to do this at the time of definition

Numeric Literals

Fixed values written directly in code, like 42 or 3.14

int (integers)

A datatype that stores whole numbers (integers); typically 4 bytes (PRECISION)

float

A datatype that uses decimal numbers with ~7 digits of precision (PRECISION)

double

A datatype that uses more precise decimal numbers with ~15–16 digits of precision

Scientific Notation

Use E for powers of 10. Example: 2.1E14 means 2.1×1014

Naming Rules

Names are case-sensitive, cannot start with a number, and cannot use symbols like $ or spaces

Basic Operators

• +, -, * (multiplication), / (division), and % (modulus).

Integer Division

Dividing two int values discards the remainder. Example: 9 / 4 results in 2

Modulus (%)

Yields the remainder of a division. Example: 14 % 4 is 2

Increment/Decrement

• Post-increment (x++): Use the current value, then add 1.

• Pre-increment (++x): Add 1 first, then use the new value.

Compound Assignment

• Shorthand like first_int += second_int (same as first_int = first_int + second_int).

Constants (const)

Values that cannot be changed once defined. Using these avoids Magic Numbers (unexplained literals in code).

Roundoff Error

Small errors caused because most real numbers cannot be stored exactly in binary.

Boolean (bool)

Stores true (internally 1) or false (internally 0).

Character (char)

Stores a single character in single quotes. Example: 'A'.

ASCII Code

The numeric representation of characters. Example: 'A' is 65.

Escape Sequences

• Start with a backslash to represent special characters like \n (newline), \t (tab), or \' (single quote).

Casting

Converting between types.

• Implicit: Automatic conversion (e.g., double x = 10;).

• Explicit: Using static_cast<type>(value) to avoid compiler warnings and data loss.

String Manipulation

• concatenation

• zero-based indexing

Concatenation

Using + to join strings. Warning: You cannot concatenate two string literals like "Alex" + "ander" directly.

Zero-based Indexing

The first character is at index 0. Example: In "John", name is 'o'.

length() / size()

• Returns the character count.

empty()

Returns true if the string is ""

substr(start, length)

Extracts a portion. Example: "Hello".substr(1, 3) is "ell".

find(str) / rfind(str)

Returns the index of a substring or string::npos if not found.

push_back(char) / pop_back()

Adds or removes a character at the end

size_t

A special unsigned integer type for sizes and indexes that matches the system's architecture.

stod(str)

Converts a numeric string to a double.

cin >>

Reads input until whitespace. Can be "chained" (e.g., cin >> bottles >> cans;).

getline(cin, variable)

Reads an entire line, including spaces, until the Enter key is pressed.

Prompts

Messages printed to the user telling them what to input.

Relational Operators

<, <=, >, >=, == (equality check), and != (not equal).

Lexicographic Ordering

Comparison based on ASCII/dictionary order.

• Uppercase comes before lowercase ("Z" < "a").

• Spaces come before printable characters.

• Numbers come before letters.

• Shorter strings are "less than" longer strings if they are prefixes.

  • spaces → numbers → uppercase → lowerspace

• EX: Tom < Richard => false, R is before T in the alphabet

Math Libraries

• <cmath>: sqrt(x), pow(base, exp), round(x).

• <algorithm>: max(a, b), min(a, b).

What is the primary skill of a computer programmer, according to the PIC 10A materials?

Problem solving

What is the specific role of the << operator when used with cout?

It is the insertion operator that sends data into the output stream.

What is the standard convention for the return value of main() to signify that a program finished successfully?

0

Which C++ data type is specifically used to store a sequence of characters or text?

string

What is the limitation of using cin to read string input from a user?

It only reads one word and stops at the first space character.

Which C++ operator is known as the 'extraction operator' used to receive data from cin?

»

What is the difference between variable 'declaration' and 'assignment'?

Declaration sets aside memory and names the variable; assignment stores a specific value in that memory.

In C++, the first assignment of a value to a variable is formally called _____.

Initialization

How does the = operator in C++ differ from its meaning in mathematics?

In C++, it is a value-assigning operation rather than a statement of logical relationship.

What is 'syntactic sugar' in the context of programming languages?

A syntax feature that is not strictly necessary but makes the code easier to write or read.

Why is it illegal to name a variable 3dGraph in C++?

Variable names cannot start with a number.

Identify the error in the variable name MixedUp#3.

It contains an illegal symbol (#).

Approximately how many decimal digits of precision does the float type provide?

7

How many bytes of memory are typically used by the double data type?

8 bytes

In C++ scientific notation, what is the meaning of the value 2.1E14?

2.1×10^4

Why is 0.5 preferred over 1/2 when writing decimal fractions in C++?

The expression 1/2 performs integer division and results in 0.

What is the result of the integer division 9 / 4 in C++?

2

If x = 5, what are the values of a and x after the operation int a = x++;?

a=5 and x=6

What is the outcome of a 'pre-increment' operation like ++x?

The value of x is incremented first, then the new value is used in the expression.

What is the result of the expression -27 % 4 in C++?

-3

The shorthand first_int += second_int; is equivalent to which full assignment statement?

first_int = first_int + second_int;

Why do computers experience roundoff errors with decimal numbers like 0.1?

0.1 has an infinite repeating representation in binary (base 2), making exact storage impossible.

Which C++ keyword is used to define a value that cannot be changed during program execution?

const

What is a 'magic number' in programming, and why is it considered bad practice?

An unexplained numeric constant in code; it makes the program harder to maintain and understand.

Internally, how does C++ store the boolean value false?

0

Which character literal syntax is required to store a single character in a char variable?

Single quotation marks (e.g., 'A').

What is the ASCII value associated with the character 'A'?

65

If a char variable letter holds 'A', what is the result of letter = letter + 1;?

‘B’

What is 'implicit casting' in C++?

An automatic type conversion performed by the compiler, such as assigning an int to a double.

Which C++ function is used to perform a safe, explicit type conversion to avoid compiler warnings?

static_cast

Which header file must be included to use functions like sqrt and pow?

<cmath>

In the cmath library, how does the round(x) function behave if x is exactly halfway between two integers?

It rounds away from zero (e.g., -2.5 becomes -3).

What are the inputs and output of the pow(b, p) function?

It takes two double inputs (base and exponent) and returns the base raised to the power of the exponent.

Which header file contains the std::max(a, b) and std::min(a, b) functions?

<algorithmn>

What is the default value of a string variable if it is declared but not initialized?

An empty string ("").

Unlike fixed-size types like int, the string type uses _____ memory allocation.

Dynamic

What is the result of concatenating "Yesom" + "Park" using the + operator?

“YesomPark”

Why is the statement string name = "Alex" + "ander"; illegal in C++?

You cannot directly concatenate two string literals using the + operator.

In C++ strings, what index is used to access the very first character?

0

Which string member function returns the total number of characters in the string?

length() or size()

For a string s = "Hello", what is the result of s.substr(1, 3)?

“ell”

What happens if you omit the second argument in the substr(start) function?

It returns all characters from the start position to the end of the string.

Which C++ function is used to read an entire line of text, including spaces, from the keyboard?

getline(cin, variable_name)

Which string member function adds a single character to the end of a string?

push_back(char)

What does the function find(substring) return if the specified substring is not found in the string?

string::npos

What is the primary characteristic of the size_t integer type?

It is an unsigned type whose size depends on the system's architecture (32-bit or 64-bit).

What is the purpose of the stod() function in C++?

To convert a numeric string into a double value.

What does a comparison between two values using relational operators (like < or ==) return?

A boolean value (true or false).

In lexicographic ordering, which is considered 'less': uppercase 'Z' or lowercase 'a'?

Uppercase 'Z'

How are strings of different lengths compared lexicographically if one is a prefix of the other?

The longer string is considered greater.

Relational Operators

Used to compare both numbers and strings. The results are returned as boolean values (true/1 or false/0

Relational Operators and Boolean Results

• > (Greater than), >= (Greater than or equal).

• < (Less than), <= (Less than or equal).

• == (Equality check): Returns true if values are identical.

• != (Not equal).

Comparison vs. Assignment

The single equals sign (=) is used for assignment (e.g., x = 5 sets x to 5), while the double equals sign (==) is a logical test (e.g., x == 5 asks "Is x equal to 5?").

Comparison Logic

• Strings are compared letter by letter, from left to right. Comparison stops at the first differing character.

• If one string is a prefix of another, the longer string is considered "greater" (e.g., "John Doe" > "John").

• Warning: To ensure correct comparison, at least one of the values must be a std::string variable; comparing two string literals directly may lead to unexpected results on some compilers.

Flow control

determines the order in which instructions are executed. While code usually runs top-to-bottom, flow control allows the program to skip code, repeat actions, or make decisions.

Flow control typed

• Conditional Statements: if, else if, else.

• Loops: while, for, do-while.

• Function Calls: Jumping to and returning from different parts of the code.