proramming notes

8/11/2019 Proramming Notes

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IDEIntegrated Development Environment

Enables programs to run, that you built

1. PreprocessingPreprocessor replaces directive with actual library code

2. CompilingReads .c and makes it executable

3. LinkingLinks to function calls

/* My first program */

#include #include

int main (void){

printf ("Hello World");system ("pause");

return0;}

there are two types of functions:

library and program

#include

stdio standard input/output library for keyboard or file input/outputstdlib any call to system

main ()

main, represents the main program

statement:

command that ends in ;

compound statements are between { }this shows where main begins and ends

printfwrites text to the screen

f stands for formatted

Comment

anything written in the comment will be ignored by the compiler

can be used to explain code// single line comment

/*

multiple level comments

*/

/* anything between these will be ignored by the complier */

system (pause);

makes the program pause, until you let it go again

return 0;


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status code given to the operating system

will work without it

Format of a simple program

int main ()

{

}

C is made up of 3 features:

- Directives

o edit commands that modify the program prior to compilation (#include)

o begins with # and no ;- Functions- blocks of executable code (such as main)

o Only main is mandatoryo int main(void), int means that the main function returns an integer value

o return 0; this statement causes the main function to terminate and returns a value

of 0.

- Statements commands to be performed

Identifiers

names of variables, functions, and macros

may contain letters, digits, & underscores must not begin with a number

up to 31 characters

Note: job Job JoB are different identifiers

special case sensitive identifiers that have meaning to the compiler, can't be used as variables

Data Types

int (4 bytes)

ointegers, or whole numbers

float or double

ofloating point, or real numbers

ofloat = 4 bytes

odouble = 8 bytes

How information is stored

binary

1 binary digit is a bit

8 consecutive bits are a byte

o 1 byte can represent 28=256 different values


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Assignments

= assign the right side to the leftex.

int height; (declare it first, if you dont declare it will be garbage)height =8;

Variable Declaration

give it a type give the variable a name

Note: if you dont assign a variable a value, it equals to nothing, or garbage

ex. int a;

int main ()

{

}

Constants

also known as macro definition use all capitals no equal sign or semicolon

ex.

#define CONSTANT 166

return #;

return 0;o everything is fine

return -1;o something went wrong, exist the program

ex.if (terms< 1 ){

printf(invalid input!\n);return -1;

}

Error Types

syntax errors

occur during compilation ex. missing semicolon

run time errors

complies successfully, but will crash on execution

ex. out of bounds loop ex. open non-existent file x/0 number too large to represents the file doesnt exist and you try to extract info


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logic errors

compiles successfully, will run, but not give out the correct input ex. - should be an == ex. if should be an else if

printf

in stdio library used to print stuff to the screen f stands for formatted

\nnewline

\asound an alarm

\bbackspace one character

\thorizontal tab

\\to print a single \

Conversion specifier

%d for int

%f for floats and doubles

ex.int a = 3;double b = -13.;

printf(value of a is %d\nvalue of b is %f, a, b);

Output:

value of a is 3

value of b is -13.000000 (10 digits including -)

ex.int a, b;a=7;b=9;printf(a+b= %d\n, a+b);

output 16

Conversion Specification

%m.pX

%-m.pX

m- number of characters

p- precision, so how many decimal places

X- conversion specifier

d- int

o default p=1

f- float or double

o default p=6ex.a=3.1;printf(%4.2f\n, a );printf(%6.4f\n, a );


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printf(%8.6f\n, a );printf(%10.8f\n, a );

3.10

3.1000

3.100000

3.09999990


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ex.

x=x+1; the following are equivalentx+=1;++x;x++;

Expression Evaluation

precedence the order that operators are evaluated

associativity the direction of the evaluation

precedence operator associativity

highest () L to R++--(post) L to R++--(pre) R to L

! (logical NOT) L to R+-(unary) R to L

*/% L to R+ - (binary) L to R

> >= <


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}

math.h

requires #include

cos(x), sin(x), tan(x) x in radians

sqrt(x) square root

fabs(x) absolute value

exp(x) exponential log(x) natural logarithm

log10(x) log base 10

pow(x,y) x raised to power y

M_PI

M_LN2 natural logarithm of 2

Logical Expressions

equal ==

not equal !=

logical NOT ! (unary)

logical AND &&

logical OR ||

if

performs action listed if true

ex.if (x


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ex.which does the else belong to?if (y != 0) {

if (x != 0)result =x/y;

}else

printf(Error);first, if no brackets it would go the second

ex.#include intmain(){

inthr;intmn;intmm;intmhr;intphr;

printf ("Enter a time (hr min):");

scanf ("%d %d", &hr, &mn);

printf("am (1) or pm (2):");scanf("%d", &mm);

phr=hr+12;

if(hr == 12)printf ("Military time; %.2d:%.2d", hr*(mm-1), mn);

elseif(mm>1)printf("Military time; %.2d:%.2d", phr, mn);

else

printf("Military time; %.2d%:%.2d", hr, mn);

return0;}

switch statement

alternative to if/else

switch (integer expression) {

case label:

break;

default: like else

ex. gradesif (grade100)

printf(Grade is out of range\n);else if (grade >=80)


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printf(Letter grade: A\n);else if (grade >=70)

printf(Letter grade: B\n);else if (grade >=60)

printf(Letter grade: C\n);else if (grade >=50)

printf(Letter grade: D\n);else

printf(Letter grade: F\n);

switch (grade/10) {case 8: case 9: case 10:

printf(Letter grade: A\n);break;

case 7:printf(Letter grade: B\n);break;

case 6:printf(Letter grade: C\n);break;

case 5:printf(Letter grade: D\n);break;

default:printf(Letter grade: F\n);break;

}

break and continue

ex.int main ( ) {

int sum=0, count=0, a;do {

printf(Enter a value: );scanf(%d, &a);

if (a==0) break; //leave the do while loop

in (a


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if (a>b) true

if (!(a>b)) false

if (a>b && a*b==1) false

if (a>b || a*b==1) true

ex.

if (a-b ==0) is equal to

if (!(a-b))

ex.int a=0, b=2, c=4;if (a= c-b)

printf(%d\n, b);else

printf(%d\n, c);

printf(%d\n, a==c-b);

Answer:2 assigns a new value of 2

1 logical, so its true, therefore its 1

Loops

while

do while

for

while

checks condition before entering the loop

continues to loop until the condition becomes falseex.int i= 0, sum=0;printf(enter an integer (-1 to end): 0;scanf(%d, &i);while (i>= 0) {

sum += I;printf(enter an integer (-1 to end);scanf(%d, &i);

}

printf(the sum is %d\n, sum);

do while

test the condition at the end of the loop

loop is executed at least onceex.do {

sum += I;printf(enter an integer (-1 to end);scanf(%d, &i);

} while(i>=0)


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printf(the sum is: %d\n, sum);

for

designed for controlled repetitionex.int i, j=0;for (i=0; i< 10; i++) {

j+=I;}

int i=0, j=0;while (i


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} while (n != 0);return 0;

}

output if n=3

1

1 2

1 2 3

Number Systems

Base 10

10 digits, 0 -> 9

Base 7

7 digits

ex. 157= (1x71) + (5x 70)

=12

binary

base 2ex. 111111112= 255

hexadecimal

0 1 2 3 4 5 6 7 8 9 A B C D E F 10 11

16 = 24

every four digits of binary (right to left), is equal to one of hex

o just like if it was 8, it would be equal to 3 digits of binary

ex.

34D16

= 11 0100 1101

characters

data type: charex.

char c1, c2, c3;c1= f;

c2= F; these are different characters

c3=4; the character 4, not the value

ASCII Character Set

American Standard Code for Information Interchange Characters stored in 1 byte of memory


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ex.char c1, c2;c1= f;c2=102;c3= f;

printf(c1 is: %d\n, c1);printf(c2 is: %d\n, c2);

printf(c2 is: %c\n, c2);printf(c2 is: %d\n, c3);

output

c1 is: 102

c2 is: 102

c2 is: f

c3 is: 102

putchar();

alternative to printf

prints out one character at a time

print variables no

characters need

ex.char a 61 =;


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putchar(a); value of a=61putchar(61);putchar(=);

output

===

getchar();

alternative to scanf

grabs one character from the keyboardex.printf(enter two characters: );c1= getchar();c2= getchar();c3= getchar();

ex. # of keystrokes#include intmain (){

intc, i=0;

printf("Type whatever you want: ");do{c= getchar();i++;

} while(c != '\n');

printf("\n\nYou typed %d keystrokes (including the return/enter key \n\n", i);

return0;}

file input and output

FILE * filename;

data type

* = pointer

name of file, that you make up

filename = fopen (avg.dat, r);

fopen, opens the file on your computer somewhere

fclose would close the file

avg.dat, is what the file is called, but in some computers you have to write out the whole path

r= read only

w= overwrite

a=append/add

EOF

end of file

fscanf returns a special character at the end of a file

ex.while (fscanf(in, %d, #) != EOF) {


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}

File doesnt exist

in_file= fopen(avh.dat, r);

if (in_file == NULL) {

printf(avh.dat does not exist!);return -1; }

fscanf

reads data from a file

int a, b, c;FILE * input;input = fopen (nums.txt, r);

fscanf(input, %d, &b, &d);

printf(average: %d\n, (a+b+c)/3);

fclose (input);

fprintf

prints into the file

must use w or aex.int i=1, j=4;FILE*out_file;out_file=fopen (data.out, w);

fprintf(out_file, %d\n, i);fprintf(out_file, %d\n, j);

fclose (out_file);

functions

library functions

user defined functions

use the function like pow(x,y) or sin(x)

the value of a inside a function will carry through to the mainex.#include

intrund (doublea);

intmain (){

doublea;

printf("Enter a number: ");scanf("%lf", &a);


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printf("rounded to the nearest whole number: %d", rund(a));

return0;}

intrund (doublea) {if(a>0.)

return(int)(a+.5);else

return(int)(a-.5);}

ex.#include #define FILE_NAME "/Users/Alicia/Documents/Dropbox/APS106-2013/7-Midterm/grades.txt"

/* function declarations */intreadGrades(intnum_of_grades);intwriteGrade(intgradeAdd);

intmain (void)

{ intchoice, num;intgrade;interror = 0;

printf ("\n");

while(1){printf ("Would you like to (1) view or (2) add to your grade history (3) exit?: ");scanf ("%d", &choice);

switch(choice) {

case1:printf ("How many grades would you like to read (0 for all)?");scanf ("%d", #);error = readGrades(num);if(error)

printf("There was an error reading the file. \n");break;

case2:printf ("What grade would you like to add?");scanf ("%d", &grade);error = writeGrade(grade);if(!error)

printf("%d was added to the grade file. \n", grade);break;case3:

return0;default:

printf("Incorrect input \n");}if(error){

printf("An error has occurred in your program.\n");break;

}}


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return-1;}

intreadGrades(intnum_of_grades){

inti, grade;

FILE *in;in = fopen (FILE_NAME, "r"); //Can use just grades.txt if running from local directory.

if(in == NULL) {printf ("file doesn't exist\n");return-1;

}if(num_of_grades == 0){

while(fscanf(in, "%d", &grade) != EOF) {printf ("%d ", grade);

}}else{

for(i=1; i


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Arrays

Bubble sort

2D arrays

o dont need first dimension to be initializedEx. initialize arrays

int N,n,i;

char *Noble[] = {"Helium", "Neon", "Argon","Krypton"};

N = 4;

for(i=0; i < N; i++) {

n=0;while(Noble[i][n] != '\0') n++;

printf("%c%c %d\n", Noble[i][0], Noble[i][1], n);

}

Addresses

- 1 bit is either a 1 or a 0- 1 byte = 8 bits

- char 1 byte- int 4 bytes

- double 8 bytes- pointer 4 bytes- sizeof = gives the size of something in terms of bytes

Pointers

4 bytes

& address operator

o the address of that value

o goes in front of an int, float, char

* indirection operator

o the value of that address

o goes in front of a pointer to pass the variable, you have to pass the address of the variable

o call by reference

arithmetic

o a[2]= *(a+2)

theres no point of adding addresses, but subtract can be useful

Ex. char c= r;

char *c_ptr;

c_ptr= &c;

printf(value %c\n, c);

printf(value %c\n, *c_ptr);

printf(address %c\n,&c);

printf(address %c\n, c_ptr);

value r

value r

address 0012FF7C


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address 0012FF7C

Ex.

//doesnt return the negative of the argument, but makes it negative inside the function.

#include

void negate (int *);

int main ( ) {

int i=3;

printf(\n\n i = %d, i);

negate(&i);printf(\n\n i = %d, i);

return 0;

}

void negate (int *j) {

*j = -*j;

return;

}

string.h

#include Strcpy - copies the string s2 into the string s1 strcpy(str2, "abcd"); /* str2 now contains "abcd"

*/

Strncpy: copies str2( starting from n) into str1: strncpy(str1, str2, n);

Strlen - returns the length of a string len = strlen("abc"); /* len is now 3 */

strcat- appends the contents of the string s2 to the end of the string s1. It returns s1 (apointer to the resulting string). strcpy(str1, "abc"); strcat(str1, "def"); /* str1 now contains

"abcdef" */

strcmp -Testing whether str1 is less than str2: if (strcmp(str1, str2) < 0) /* is str1 < str2? */Testing whether str1 is less than or equal to str2: if (strcmp(str1, str2)


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else

*y = 'a'+i;

y++; }

*y = '\0';

puts (x);

enter 4, output: aBcD

if yu use puts(y) instead of puts(x) then yu get nothing (cause y starts at the end and x starts at the

beginning.

Struct

struct Elmnts { int num;

char symbol;

float mass; };

int main(){ int i;

struct Elmnts *ptr;

struct Elmnts fewElmts[] = {{5,'B',10.811},{6,'C',12.011}, {7,'N',14.007}, {8,'O',15.999}, {9,'F',18.998}};

ptr = fewElmts; printf("%c\n",ptr->symbol);

printf("%d\n",(++ptr)->num);

ptr++;

printf("%d\n",++(ptr->num));

ptr++;

printf("%0.3f\n",(ptr++)->mass);

printf("%c\n", ptr->symbol);

return 0;

}

Output:

B

6

8 //not 15.007, ptr address not the value

15.999

F

Dynamic Memory Allocation#include

mallocAllocates a block of memory but doesnt initialize it.

Eg. A call of malloc that allocates memory for a string of n characters:

char * p;

p = malloc(n* (sizeof(char) + 1));

callocAllocates a block of memory and clears it to 0.


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Eg. A call of calloc that allocates space for an array of n integers:

a = calloc(n, sizeof(int));

reallocResizes a previously allocated block of memory

eg; realloc(a,sizeof(int)*5); /*characters will only have 5 elements*/

realloc(*ptr, size);

free- unallocates the allocated memoryE.g. free(a);

Random Number Generator

#include

int number;srand ((unsigned) time(NULL));

number = rand()%100+1;

(Num frm 1-100)

number = rand ( )%4;

(Numb from 0-3)