L1: C Warmup

Question 1

Parts of the C Standard Library, Categorized (15)

Answer 1

General:

• stdio.h - input/output
• stdlib.h - General Functions
• math.h - Math Functions

System:

• stddef.h
• stdarg.h
• signal.h
• setjmp.h
• limits.h
• locale.h
• time.h

Variables:

• float.h
• string.h

Testing/Debug:

• assert.h
• errno.h
• ctype.h

Question 2

C Standard Library:

Input/Output Library

Answer 2

stdio.h

Question 3

C Standard Library:

General Function Library

Answer 3

stdlib.h

Question 4

C Standard Libary:

Testing and Debug Function Libraries

Answer 4

assert. h
errno. h
ctype. h

Question 5

C Standard Libary:

System Libraries

Answer 5

stddef. h
stdarg. h
signal. h
setjmp. h
limits. h
locale. h
time. h

Question 6

C Standard Library:

Variable Libraries

Answer 6

float. h
string. h

Question 7

Fundamental Principles of Strings

Answer 7

• Strings are arrays of char’s where the last char is ‘\0’
• Declaration: char s[], s is an array variable that points to the array
• Assignment:
  
  • s = “abc”
• Assigment with an empty string:
  
  • s = “”
  • s actually points to the null terminator “\0”
• Assign 0:
  
  • s = 0
  • s is a null pointer, points nowhere

Question 8

Array Declarations

Answer 8

• Format:
  
  • type name[size]
  • example: char A[4]
• Once declared, A is a constant that can’t be modified
• The name ‘A’ is a pointer to the first element in the array

Question 9

Array Declarations:

Undefined Declaration

Answer 9

Declared as a pointer:

char *B

or

char B[]

This allocates no storage, B is undefined

Question 10

Primitive Types:

Integers

• types
• declaration
• values
• constants

Answer 10

• int
  
  • declaration: int i;
  • 16 or 32 bit (or 64)
  • Constants:
    
    • 0, 1, 10, 0xF, 010
• long,
  
  • end in ‘L’
  • 32, 64, or 128 bit (2x as long as int)
  • Constants:
    
    • 0L, 1L, 10L, 0xFL, 010L

Question 11

Useful Functions:

Characters

(5 functions)

Answer 11

Library: ctype.h

Functions for testing a character against ranges:

isalpha(‘a’)

isdigit(‘0’)

iswhite(‘\t’)

isupper(‘A’)

islower(‘a’)

Question 12

Useful Names and Functions:

Strings

Answer 12

include ‘<‘string.h’>’

• Concatenate:
  
  • strcat(s, “more”)
• Copy String:
  
  • strcpy(s, “more”)
• Compare:
  
  • strcmp(s, t)
  • returns 0 if equal, -1 if s<t>t</t>
• Length of String
  
  • strlen(s)
• Find character in string:
  
  • strchr(s,c)
  • Returns pointer to first char in s that equals character c (or returns NULL)

Question 13

Fundamentals of Arrays

(How Array Pointers Work)

Answer 13

• int A[4]
  
  • Allocates room on stack, makes A point to first element
• *A = 21
  
  • Stores the value 21 where A points to the first element
• *(A+1) = 6
  
  • Stores the value 6 at the next int beyond where A points
• Arrays are pointers to the first element
• *(A+n) is equivalent to A[n]

Question 14

Primitive Operations:

Bitwise Operations

Answer 14

• Bitwise AND:
  
  • i & j
• Bitwise OR:
  
  • i | j
• Bitwise NOT:
  
  • ~i
• Bitwise XOR:
  
  • i ^ j
• Bitwise Left Shift, Right Shift:
  
  • a << b shift bits of a by b bits
  • a >> b

Question 15

C Primitive Types

Answer 15

• Integers
  
  • int, long
    
    • 32, 64 bit respectively(outdated)
• Characters:
  
  • char
    
    • 8-bit
• Arrays
• Pointers
  
  • address of integer: int *p
  • address of character: char *q
• Functions
  
  • Names of subroutines
  • form:
    
    • returntype name(arg1, arg2,…){ //code}

Question 16

C Primitive Types:

Arrays

• Declarations
• Values

Answer 16

• Declaration:
  
  • type name[size]
  • Name with new space allocated
  • This is a constant
  • ex: char A[10] , int I[8]
• Empty Declaration:
  
  • type name[]
  • Pointer to an array, name to share old space
  • This is a variable, can be redirected
  • ex: char B[], int J[]

Question 17

Primitive Types:

Characters

• declaration
• value
• Special Character examples

Answer 17

• Declaration:
  
  • char c;
• Value:
  
  • 8-bit characters
• Special Characters:
  
  • ‘a’ normal char
  • ‘\n’ newline char
  • ‘\t’ tab
  • ‘\0’ null terminator
  • ’\’ escaped backslash

Question 18

Useful Names and Functions:

Utility Functions

Answer 18

from the “stdlib.h” library

• atoi(s)
  
  • convert s to an integer (0 if not a number)
• malloc(n)
  
  • allocates n bytes of new memory and returns a pointer to it
• free(p)
  
  • frees the block of memory that p points to
• exit(status)
  
  • end the program, with the specified status
• getenv(“PWD”)
  
  • get the specified environment(shell) variable

Question 19

How to use a routine from a different file

without referencing a header

Answer 19

• Declare a function prototype that matches the function declaration in the other file:
  
  • int myMethod(int n);
• When compiling, link the other file
• example:
  
  • cc -o sum sum.c main.c
  • This allows the program in “main” to use a function from sum.c, as long as it is declared
• It’s easier to just include other files

Question 20

Steps of Using

“while” logic

Answer 20

1. Create Initial State
   
   • int s[4];
   • int i, n;
   • n = 4; i=0;
2. Declare While loop with condition
   
   • while( i<n …>
   </n>
3. Do work within the while loop
   
   • s[i] = i * i;
4. Advance the state
   
   • ++i;

Question 21

Primitive Operations:

• Incrementing
• Decrementing
• Post/Pre
• Variable Types

Answer 21

• Increment:
  
  • Pre: ++i, returns new value
  • Post: i++, returns old value
• Decrement
  
  • Pre: –j, returns new value
  • Post: j–, returns old value
• Applies to types:
  
  • int
  • long
  • char
  • pointers

Question 22

Defining a Constant in C

Answer 22

define NAME (value)

example:

*convention is to use upper case for the name

Question 23

Compiler:

Compile a program to a specified name

Answer 23

Use the ‘-o’ flag when compiling, followed by a name

example:

cc -o myProgram sub.c main.c

will compile both sub.c and main.c into an executable

program called “myProgram”

Question 24

Useful Names and Functions:

Input/Output (I/O)

Answer 24

Library: stdio.h

• Named Values:
  
  • NULL = 0
  • EOF = -1
• Standard File Descriptors:
  
  • stdin
  • stdout
  • stderr
• Functions:
  
  • getchar() - gets next char from file or EOF
  • putchar(c) - write one char to file
  • printf(…) - high level output formatting to file
  • fgets() - read one line from file

Question 25

C Pointer Variations

Answer 25

• Normal:
  
  • p
  • Returns pointer to itself
• Pointer:
  
  • *p
  • Returns thing pointed at
• Pointer to a field within a structure:
  
  • q->f
  • Returns field f of structure q
• Address Pointer:
  
  • &x
  • Returns address of x