2: variables and data types - amazon s3 · lecture 2 ece15: introduction to computer programming...

ECE15: Introduction to Computer

Using the C Language

2: Variables and Data Types

A. Orlitsky and A. Vardy, based in part on slides by

A. Orlitsky and A. Vardy, based in part on slides by S. Arzi, G. Ruckenstein, E. Avior, S. Asmir, and M. Elad

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 2

printf()scanf()

3+4

& much more

Lecture 5 ECE15: Introduction to Computer Programming Using the C Language

❖ Writing

❖ Reading

❖ Variables and data types

‣ Text ‣ Integers ‣ Reals ‣ Characters ‣ Strings

❖ Rudimentary file input/output

3

Outline

Writing (Printing)❖ C printing function printf() “print formatted”

❖ Name shared by several programming languages

❖ Prints

‣ Text (“Hello world”)

‣ Integers

‣Reals

‣Characters

‣Strings


Printing Text


printf(“Hello world!\n”); Hello world! >

printf(“Hello world!”); Hello world!>

printf(“Hello\n world!\n”); Hello world! >

printf(“Hello\nworld!\n”); Hello world! >

Integer Constants


❖ Used to print, write in program, type

‣ 7

‣ -13

‣ 1234 (not 1,234)

7

Printing Integers


❖ Format using %d (decimal) or %i (integer)

❖ %3d - use at least 3 locations

8

printf("%d", -13);

printf("my %i cents", 2);

printf("%d+%d=%d", 1, 2, 1+3);

-13

my 2 cents

1+2=4

printf("#%d#%3d#%-3d#",1, 2, 3);

#1# 2#3456#

printf("#%5.3d#%-5.3d#", 1, 2); # 001#002 #

printf("%d", 2*3+4); 10

printf("#%d#%3d#%3d#",1, 2, 3456);

#1# 2#3 #

left adjust

Precede w. 0’s

printf("-13");

More math later

Same as

Format statement Regular text gets printed normally. %d, %i, etc. don’t get printed. They determine how arguments after “...” get printed.

Formatting errors


❖ %d and %i indicate how subsequent arguments get printed ❖ # of %d %i should match # subsequent arguments ❖ What if these numbers don’t match?

9

printf("%d", 1, 2); Compilation warning

printf("%d %d", 1); Compilation warning 1 73858

1

mismatch.c

Variables


❖ So far, everything fixed and rigid, nothing changes

‣program always prints same thing (“Hello, world”, -13)

❖ Need something more flexible, dynamic

‣Print different values, read user input

❖ Variables ‣Hold information ‣ Take user input ‣Can change with time

Data Types


❖ All constants and variables have a type ‣ Integer, real number, character, string

❖ Type determines ‣# memory bytes allocated ‣ Interpretation / meaning of the bits stored in these bytes ‣Operations allowed

❖ Variables must be declared ‣ type, name, optional initial value

‣ Instructs compiler to ๏ Allocate right # memory cells ๏ Interpret content of these cells according to type ๏ Associate variable name with these cells

int num,sum; double weight = 0.0; char digit = '4';

NowShortly

int❖ Basic integer type (more types later) ❖ Declaration

❖ Uninitialized (contains previously stored value) ❖ Initialization:

‣ At declaration

‣ Assignment

❖ Printing: same as constants


int year; int temperature, humidity;

printf("%d", year);

int a=0;

int a; a=0;

int a=0, b=1;

int a, b; a=b=0;

int a, b; a=0; b=1;

Hint = does not mean equal. a = 5 means store 5 in the variable called a.

Hint Initialize or assign value to a variable before using its contents.

Quiz


❖ What’s printed?

13

#include <stdio.h>

int main() { int a=0, b, c, d, e, f; b=1; c=d=2; printf("a=%d\n", a);

printf("b=%d\n", b);

printf("c=%d\n", c);

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

printf("e=%d\n", e);

printf("f=%d\n", f);

return 0; }

a=0

b=1

c=2

d=2

e=589

f=-2381039

Or whatever stored before

quiz.c

Likewise

Reading Integers


❖ scanf() with %d (or %i)

14

Always (for now..) use scanf with & - stores value in that location

#include <stdio.h>

int main() { int myvar;

printf("Type an integer: ");

scanf("%d", &myvar);

printf("It is: %d\n", myvar);

return 0;

}

scanf1.c

Think of &myvar as the address of myvar More later

Non-integer input


15 You typed 15

rest left for future scanf’s

%d first skips white space

1.5 You typed 1

whatever stored before

#include <stdio.h> int main() { int value; printf("Type an integer: "); scanf("%d", &value); printf(“You typed %d\n", value); return 0; }

1b

b < .5

1,234

You typed -183793

scanf1.c

15 You typed 15

Then stops reading when encounters non-integer

Ignored

Reading More Values


#include <stdio.h>

int main() { int value1, value2;

printf("Now gimme two: ");

scanf("%d%d", &value1, &value2);

printf("Their sum: %d\n", value1+value2);

return 0; }

scanf("%d %d", &value1, &value2);

❖ Spaces between %d`s in format string don’t matter same

scanf2.c

Maximum Field Size


Integer between % and d specifies maximum # digits read

scanf("%2d", &a);

scanf("%1d%d", &a, &b);

a=11

123 a=12

123 a=1 b=23

scanf("%1d", &a); scanf("%d", &b);

123 a=1 b=23

same

Field Separators


❖ Text after %d is expected and read after integer is read

❖ ALLOWED modifications ‣ Add space after separator

‣ Change or remove existing spaces in and around separator

❖ DISALLOWED ‣ Add space before separator

‣ Change or remove (non-space) separator symbols

scanf("%d,%d", &a, &b); 1,2 a=1 b=2

1xy2 a=1 b=2

1xy 2

a=1 b=2

scanf("%dxy%d", &a, &b);

1 xy2

a=1 b=#&<)

1, 2 a=1 b=2

1 ,2

1 2 a=1 b=*)%-

scanf("%d x y %d", &a, &b); 1 x y 2 a=1 b=2

a=1 b=2

1.2 a=1 b=!?^)

1 xy2 a=1 b=<?)!

scanf("%d,%d", &a, &b);


scanf("%d,%d", &a, &b);


scanf("%d,%d", &a, &b);

scanf("%dxy%d", &a, &b); 1x2 a=1 b=<?)!

Remember mainly this

part!

separator.c

Keep rest in mind, but

less likely to be in exams.

How Much Time Left


❖ Homework is due tonight at 23:59 ❖ Ask user for current time h:m, output time left

19

#include <stdio.h> int main() { int hour, minute; printf("Enter current time (hh:mm): "); scanf("%d:%d", &hour, &minute); printf("%d hours and %d minutes left\n", 23-hour, 59-minute); return 0; }

6 hours and 44 minutes left 17:15

Enter current time (hh:mm):

19 hours and 54 minutes left 4:5

time.c

How Many Values scanf Read?


❖ Returns # of successfully read variables

#include <stdio.h>

int main() { int numRead, firstVal, secondVal; printf("Two integers please: ");

numRead = scanf("%d%d", &firstVal, &secondVal);

printf("Read %d ints, first was %d, second %d\n ", numRead, firstVal, secondVal); return 0; }

scanf_num.c

Try entering 5a

Using # Values scanf Read


❖ Calculate average of up to 4 integers

❖ Later - better ways of doing that

21

#include <stdio.h> int main() { int a1=0, a2=0, a3=0, a4=0; int number;

printf("Enter up to 4 integers followed by *: "); number = scanf("%d%d%d%d", &a1,&a2,&a3,&a4); printf("Sum=%d, Number=%d\n",a1+a2+a3+a4,number); printf("APPROXIMATE average is %d\n", (a1+a2+a3+a4)/number); return 0; } Approximate because integer!!

average.c

Can we Print Everything?


printf(“\””);

printf(“\\n”);

printf(“%%d”);

”

\n

%d

Means How to print? Like so

” end format ” \”

\n newline \ \\

%d decimal % %%

printf(“\\\\”); \\


❖ Rest of the material about integers is important, and you should know it

❖ Yet a bit harder to memorize, hence less likely to appear in in-class midterm and exam

23

Representation of Integers


❖ Computers represent everything in binary: 0,1 ❖ Nonnegative integers: standard binary representation

‣ Reserve leftmost bit for sign

‣ For 3 bits: 0 → 000, 1 → 001, 2 → 010, 3 → 011

‣ Start with 0

‣ With n bits, represent 0 to 2n-1-1

❖ Negative integers: 2’s complement, -x represented as 2n-x

‣ For 3 bits: -1 → 111, -2 → 110, -3 → 101, -4 → 100

‣ Start with 1

‣ With n bits, represent -1 to -2n-1

24

Though not on exam, you should know this!

Size of int

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language25

❖ Standards don’t determine size of int

❖ Most compilers allocate 4 bytes (32 bits)

❖ Range: -231,…,-1,0,1,…,231-1❖ 231 = 2,147,483,648 ~ 2 Billion

❖ Often not enough

❖ How do we know # bytes?

> a.out x=2147483647 x+1=-2147483648 >

#include <stdio.h> int main() { int x=2147483647;

printf("x=%d\n", x); printf("x+1=%d\n", x+1);

return 0; } largest_int.c

byte = 8 bits

210 1,024

~thousand

220 1,048,567 ~million

230 1,073,741,824 ~billion

sizeof


❖ returns # bytes used to store object ❖ object:

‣ Type name: int ‣ Variable name: x ‣ Expression: 3*x+5

❖ Shortly use for other types

sizeof(object)

printf("Number of bytes:\n");

printf("int: %lu\n", sizeof(int)); int dummy=57; printf("dummy: %lu\n", sizeof(dummy)); printf("3*dummy: %lu\n", sizeof(3*dummy));

Number of bytes: int: 4 dummy: 4 3*dummy: 4

sizeof1.c

❖ short, long (often = int), long long (large integers)

‣ Sizes guaranteed to satisfy

Other Integer Types


sizeof(short)≤sizeof(int)≤ sizeof(long)≤ sizeof(long long)

short: 2, int: 4, long int: 8, long long int: 8

dummy: 8, 3*dummy: 8

printf("short: %lu, int: %lu, \ long int: %lu, long long int: %lu\n",

sizeof(short), sizeof(int),

sizeof(long int), sizeof(long long int));

long long int dummy=57;

printf("dummy: %lu, 3*dummy: %lu\n", sizeof(dummy), sizeof(3*dummy));sizeOfTypes1.c

Line continues

❖ Constants

‣ long - 35L, long long - 21537LL ❖ printf and scanf

‣ short - %hd, long - %ld, long long - %lld

#include <stdio.h> int main() { long int a = 5, b = 5L;

int c = 2147483648, d = 2147483648L;

long int e = 2147483648L;

long long int f=2147483648LL;

printf("a=%ld b=%ld e=%lld f=%lld\n", a,b,h,h); return 0; }

sizeOfTypes2.c

Reading & Writing Integer Types


Needed only for really long integers

✘ ✘

ü

ü ü

ü

Largest int: 2147483647

ü

❖ unsigned represents only positive integers, hence doubles the range. For example, if int occupies 4 bytes

❖ Similarly: unsigned char, unsigned short, unsigned long

❖ Same for scanf

Unsigned


int: -231,…,-2,-1,0,1,2,…,231-1unsigned int: 0,1,2,…,232-1

#include <stdio.h> int main() { unsigned int us1 = 5u, us2 = 5U, us3 = 5; printf("us1=%d us2=%u us3=%U\n, us1,us2,us3); return 0; }

unsigned.cneeded only when large

Octal and Hexadecimal Constants❖ Constants ‣ Octal - precede with 0 (zero)

‣ Hexadecimal - precede with 0x

❖ Printing

‣ Octal (%o)

‣ Hexadecimal (%x,%X)


printf("%o", 13);

printf("%x", 13);

15

d

printf("%d", 012); 10

printf("%d", 0x12); 18

Constants


❖ Floating point

❖ Scientific notation

❖ Integers (converted)

32

+13.0 -13.0.7 .7

1.23e1

1.23

.123E+2 =.123*102 = 12.3

13 Caution when printing integer as float

Printing


❖ Print: %g, %f, or %e

33

printf("%g", 24.00);

printf("%g", .174e2);

printf("%g", 7);

printf("%f", 2.4);

printf("%.2f", 2.4);

printf("%e", -24.);

24

17.4

-3.23732e-232

2.400000

-2.400000e+01

2.40

printf("#%-6.2f#", 2.4); #2.40 #

by default 6 digits after point

2 digits after point

print total of at least 6 digits including point

scientific notation .174e2=.174*102

- left

ûgcc -Wall

alerts to problem

float and double


double fraction; float width, height;

printf("%f", width);

float a=0.5;

double a; a=.13;

double a=5, b=3e-2;

double a, b; a=b=-17.23;

❖ Basic types, double provides more precision, more common

❖ Constants are double

❖ Declaration

❖ Uninitialized (contains previously stored value) ❖ Initialization

‣ At declaration

‣ Assignment

❖ Printing: same as constants (for both double and float)

Reading


❖ scanf() with %f (float), %lf (double)

35

#include <stdio.h>

int main() { double x;

printf("Real #: "); scanf("%lf", &x); printf("Typed: %g\n", x);

return 0; }

int i; double x; float y; printf("Enter int, double, and float: "); scanf("%d%lf%f", &i, &x, &y);

printf("Int: %d dbl: %f flt: %f\n", i, x, y);

❖ Reading & writing mixed types

Again!

mix.c

Representation

0|10|11001001000011111


sign exponent mantissa

3.1415926 11.001001000011111

Represented by binary floating-point expansion

Integers (42.0) and byadic fractions (42/1024) represented exactly

Other reals are approximated

You should know, but not in exams.

Other Real-Valued Data Types


sizeof(float) ≤ sizeof(double) ≤ sizeof(long double)

sizeofFloatingPoint.c

❖ In addition to double and float can use long double

❖ Standard guarantees

❖ Most compilers allocate

‣ double:8 bytes, ±5.0×10-324 to ±1.7×10308, 15 precision digits ‣ float: 4 bytes, ±1.5×10-45 to ±3.4×1038, 7 precision digits


Characters

38

❖ Constants ‣ Enclosed in ‘ ‘: 'a', 'Z', '3', '+', '#', '$' ‣ Some letters cannot be written directly, use escape: \

❖ Declaration

❖ Uninitialized (contains previously stored value) ❖ Initialization

‣Wrong:

char


char letter_name; char letter_name, initial;

char a=’d’;char a; a=’#’;

char a, b; a=b=’\b’;

char a=d; Thinks it’s a variableç

'\n'-- newline '\t'-- tab '\b'-- backspace '\a' -- bell (alert)

moves back, doesn’t erase

Forward

Printing and Reading


❖ Printing

❖ Reading

40

printf("%c", ’d’); printf("d");same as

char vowel=’H’; printf("%ca%c", vowel, ’!’); Ha!

printf("%c%c%c", ’a’,’\b’,’b’);

printf("%c%c%c%c",’\a’,’\a’,’\a’,’\a’);

b

printf("%c%c%c%c", ’a’,’\b’,’b’,’\b’); b

scanf("%c", &a1); again

scanf("%c%c", &a1, &a2); printf("%ce%c\n", a2, a1);

nt tenchar.c

char a1, a2;Assume:

❖ Character stored in one byte (8 bits)

❖ Represented as integer from 0 to 127 using ASCII (American Standard Code for Information Interchange)

Representation


Character Represented as Decimal

A 01000001 64+1=65

B 01000010 64+2=66

a 01100001 64+32+1=97

0 00110000 32+16=48

ASCII Table Free ASCII Chart

Char Desc Dec Hex Key Char Dec Hex HTML Char Dec Hex Char Dec Hex Char HTML Code

!"# NULL 0 00 ^@ $%&'( 32 20 ) 64 40 * 96 60 $%&'(

$+, Start of Heading 1 01 Â - 33 21 . 65 41 & 97 61 / &

$01 Start of Text 2 02 ^B 2 34 22 " 3 66 42 4 98 62 5 <

601 End of Text 3 03 ^C 7 35 23 8 67 43 ' 99 63 9 >

6+0 End of Transmission 4 04 ^D : 36 24 ; 68 44 < 100 64 = ©

6!> Enquiry 5 05 Ê ? 37 25 6 69 45 ( 101 65 @ ®

.8A Acknoledge 6 06 ^F / 38 26 & B 70 46 C 102 66 D ¹

36# Bell 7 07 ^G E 39 27 F 71 47 G 103 67 H ²

3$ Backspace 8 08 ^H I 40 28 , 72 48 J 104 68 K ³

0.3 Horizontal Tab 9 09 Î L 41 29 M 73 49 M 105 69 E '

#B Line Feed 10 0A ^J N 42 2A O 74 4A P 106 6A 2 "

Q0 Home 11 0B ^K R 43 2B A 75 4B S 107 6B T ¼BB Form Feed 12 0C ^L U 44 2C # 76 4C V 108 6C W ½8X Carriage Return 13 0D ^M Y 45 2D Z 77 4D [ 109 6D \ ¾$+ Shift Out 14 0E ^N ] 46 2E ! 78 4E ^ 110 6E ! π

$M Shift In 15 0F Ô _ 47 2F + 79 4F ` 111 6F a ™

;#6 Data Link Escape 16 10 ^P b 48 30 c 80 50 % 112 70 " ∞

;8d Device Control 1 17 11 ^Q d 49 31 > 81 51 e 113 71 # ≠

;8f Device Control 2 18 12 ^R f 50 32 X 82 52 g 114 72 $ ≤

;8h Device Control 3 19 13 ^S h 51 33 $ 83 53 i 115 73 % ≥

;8j Device Control 4 20 14 ^T j 52 34 0 84 54 k 116 74 & ≈

!.A Negative Acknowledge 21 15 Û l 53 35 " 85 55 m 117 75 ! &equiv;

$n! Syncronous Idle 22 16 ^V o 54 36 Q 86 56 p 118 76 ' ∑

603 End of trans. Block 23 17 ^W q 55 37 r 87 57 s 119 77 t •

8.! Cancel 24 18 ^X u 56 38 1 88 58 v 120 78 w …

6Z End of Medium 25 19 ^Y x 57 39 n 89 59 y 121 79 ( Δ

$"3 Substitute 26 1A ^Z z 58 3A { 90 5A | 122 7A " ←

6$8 Escape 27 1B ^[ } 59 3B ~ 91 5B � 123 7B # ↑

B$ Cursor Right (File Seperator) 28 1C ^\ 5 60 3C < Ä 92 5C Å 124 7C $ →

F$ Cursor Left (Group Seperator) 29 1D ^] Ç 61 3D É 93 5D Ñ 125 7D % ↓

X$ Cursor Up (Record Seperator) 30 1E ^^ 9 62 3E > Ö 94 5E Ü 126 7E & ↔

"$ Cursor Down (Unit Seperator) 31 1F ^_ á 63 3F à 95 5F ;6# 127 7F â &fnof;

HTML Codes use the #& with the decimal value followed by a semi colon. Example: @ for the @ symbol.

HTML Post Operation use the % sign and the hex value. Example: Space would be %20

To obtain codes 0-31, console Control Key is pressed while simultaneously pressing the Letter Key.

www.kellermansoftware.com Free quick reference sheets and .net components


Free ASCII Chart


!"# NULL 0 00 ^@ $%&'( 32 20 ) 64 40 * 96 60 $%&'(


$01 Start of Text 2 02 ^B 2 34 22 " 3 66 42 4 98 62 5 <

601 End of Text 3 03 ^C 7 35 23 8 67 43 ' 99 63 9 >


6!> Enquiry 5 05 Ê ? 37 25 6 69 45 ( 101 65 @ ®


36# Bell 7 07 ^G E 39 27 F 71 47 G 103 67 H ²

3$ Backspace 8 08 ^H I 40 28 , 72 48 J 104 68 K ³




$M Shift In 15 0F Ô _ 47 2F + 79 4F ` 111 6F a ™









8.! Cancel 24 18 ^X u 56 38 1 88 58 v 120 78 w …



6$8 Escape 27 1B ^[ } 59 3B ~ 91 5B � 123 7B # ↑









Free ASCII Chart


!"# NULL 0 00 ^@ $%&'( 32 20 ) 64 40 * 96 60 $%&'(


$01 Start of Text 2 02 ^B 2 34 22 " 3 66 42 4 98 62 5 <

601 End of Text 3 03 ^C 7 35 23 8 67 43 ' 99 63 9 >


6!> Enquiry 5 05 Ê ? 37 25 6 69 45 ( 101 65 @ ®


36# Bell 7 07 ^G E 39 27 F 71 47 G 103 67 H ²

3$ Backspace 8 08 ^H I 40 28 , 72 48 J 104 68 K ³




$M Shift In 15 0F Ô _ 47 2F + 79 4F ` 111 6F a ™









8.! Cancel 24 18 ^X u 56 38 1 88 58 v 120 78 w …



6$8 Escape 27 1B ^[ } 59 3B ~ 91 5B � 123 7B # ↑









Free ASCII Chart


!"# NULL 0 00 ^@ $%&'( 32 20 ) 64 40 * 96 60 $%&'(


$01 Start of Text 2 02 ^B 2 34 22 " 3 66 42 4 98 62 5 <

601 End of Text 3 03 ^C 7 35 23 8 67 43 ' 99 63 9 >


6!> Enquiry 5 05 Ê ? 37 25 6 69 45 ( 101 65 @ ®


36# Bell 7 07 ^G E 39 27 F 71 47 G 103 67 H ²

3$ Backspace 8 08 ^H I 40 28 , 72 48 J 104 68 K ³




$M Shift In 15 0F Ô _ 47 2F + 79 4F ` 111 6F a ™









8.! Cancel 24 18 ^X u 56 38 1 88 58 v 120 78 w …



6$8 Escape 27 1B ^[ } 59 3B ~ 91 5B � 123 7B # ↑









Implications


❖ Can (not recommended) use numbers instead of characters

❖ Can add and subtract

43

char let = 98;char let = ’b’;

0 ... 48 49 ... 65 66 ... 97 98 ... 127\0 ... 0 1 ... A B ... a b ... DEL

same as

printf("%d", let);

scanf("%c", &let); scanf("%d", &let);b 98same as

b98 printf("%c", let);

printf("%c", ’b’+2); d printf("%d", ’b’+2); 100

printf("%d", ’I’-’B’); printf("%c", ’I’-’B’);7

bell.c

Quiz


❖ What does the following program do?

44

#include <stdio.h>

int main() {

char c; printf("Lower case letter: ");

scanf("%c", &c);

printf("I druther type: %c\n", c + ’A’ - ’a’);

return 0;

} what.c

lower case to UPPER

0 ... 48 49 ... 65 66 ... 97 98 ... 127\0 ... 0 1 ... A B ... a b ... DEL

+ 66 - 97

-32

Quiz


❖ What does the following program do?

45

#include <stdio.h>

int main() {

char c; printf("Lower case letter: ");

scanf("%c", &c);

printf("I druther type: %c\n", c + ’A’ - ’a’);

return 0;

} what.clower case to UPPER

Skipping White Space


❖ %d reads integers, skips white space (and other non digits) ❖ %c reads characters, doesn’t skip anything ❖ What if scanf %d followed by %c

‣ Newline after int not be read by %d, read as char ❖ To skip white spaces before char, use " %c"

46

printf("Integer: "); scanf("%d", &num); printf("Letter: "); scanf("%c", &let); printf("%d %c\n", num, let);

> a.out Number: 57 Letter: 57

>

> a.out Number: 57 Letter: c 57 c >

scanf("%d %c", &num, &let);

skipWhite.c

scanf(" %c", &let);

or

Skipping Specific Input


❖ To skip specific input use * ❖ %*d skips an integer

❖ To skip specific values (at least one):

47

#include <stdio.h> int main() { int i, j; printf("Three ints: "); scanf("%d%*d%*d", &i, &j); printf("i=%d j=%d\n",i,j); return 0; }

#include <stdio.h> int main() { int i; char c; printf("Int<white>char: "); scanf("%d%*[b \t\n]%c",&i,&c); printf("i=%d c=%c\n",i,c); return 0; }

Read three integers, print first and last

scanf("%*d");

skip_b_white.c

scanf("%*[ \t\n]");

skip_int.c

Read integer, skip white spaces and b’s, and read character

getchar() and putchar()


❖ Simple way of reading and writing single characters

❖ Useful for pausing programs

48

#include <stdio.h>

int main() { char a, b; a=getchar(); b=getchar(); putchar(b); putchar(a); return 0; }

getputchar.c

Especially demos...


Strings

Strings


❖ Sequence of characters enclosed in quotes

❖ 'a' and "a" stored differently (more when study arrays)

❖ Printing

❖ Reading: when study arrays (need to allocate space)

"hello world.\n""Hi" " ?!# @" " " ""

printf("hello");

"a"

printf("%s", "hello");

printf("%d+%d%s%d\n", a, b, " equals ", a+b);

printf("\a"); printf("\b "); space, so overwrites

same as hello

1+2 equals 3

int a=1, b=2;


File Input and Output

Basic File Input / Output


❖ Read input from a file or write output to a file? ❖ Useful: long in/out, saving, consistency ❖ Simplest method (others later): ‣ a.out < file1 ‣ a.out > file2

❖ All input from file1 all output to file2 (none from keyboard / to screen)

52

#include <stdio.h>

int main() { int x, y;

scanf("%d %d", &x, &y); printf("1st: %d\n2nd: %d\n", x,y);

return 0; }

> m InFile > 7 11 a.out < InFile 1st: 7 2nd: 11 > m OutFile OutFile: No such file.. a.out > OutFile 20 11 > m OutFile 1st: 20 2nd: 11 > a.out <InFile >OutFile > m OutFile 1st: 7 2nd: 11 >

inOut.c

input read from file1

output printed to file2


❖ Writing

❖ Reading

❖ Variables and data types

‣ Text ‣ Integers ‣ Reals ‣ Characters ‣ Strings

❖ Rudimentary file input/output

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Outline

2: variables and data types - amazon s3 · lecture 2 ece15: introduction to computer programming...

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