Printf("Hello"); Same As Printf("%S", "Hello"); Hello

ECE15: Introduction to Computer Using the C Language

2: Variables and Data Types

A. Orlitsky and A. Vardy, based in part on slides by S. Arzi, G. Ruckenstein, E. Avior, S. Asmir, and M. Elad A. Orlitsky and A. Vardy, based in part on slides by & much more printf() 3+4 scanf()

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

❖ Reading

❖ Variables and data types ‣ Text ‣ Integers ‣ Reals ‣ Characters ‣ Strings ❖ Rudimentary file input/output

Lecture 5 ECE15: Introduction to Computer Programming Using the C Language 3 Writing (Printing)

❖ C printing function printf() “print formatted” ❖ Name shared by several programming languages ❖ Prints ‣ Text (“Hello world”) ‣ Integers ‣ Reals ‣ Characters ‣ Strings

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 4 Printing Text

printf(“Hello world!”); Hello world!>

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

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

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

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 5 Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 6 Integer Constants

❖ Used to print, write in program, type

‣ 7

‣ -13

‣ 1234 (not 1,234)

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 7 Printing Integers ❖ Format using %d (decimal) or %i (integer) printf("%d", -13); Same as printf("-13"); -13

Format statement printf("my %i cents", 2); my 2 cents Regular text gets printed normally. %d, %i, etc. don’t printf("%d", 2*3+4); 10 get printed. They More math later determine how arguments after printf("%d+%d=%d", 1, 2, 1+2); 1+2=3 “...” get printed.

printf("%d+%d=%d", 1, 2, 1+3); 1+2=4

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 8 Minimum Print Size

❖ %3d - use at least 3 locations

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

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

printf("#%5.3d#%-5.3d#", 1, 2); # 001#002 # Precede w. 0’s ❖ Useful for printing table

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 9 Formatting errors

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

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

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

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 10 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

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 11 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 int num,sum; double weight = 0.0; char digit = '4'; ‣ Instructs compiler to Shortly Now ๏ Allocate right # memory cells ๏ Interpret content of these cells according to type ๏ Associate variable name with these cells

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 12 int ❖ Basic integer type (more types later) ❖ Declaration int year; int temperature, humidity;

❖ Uninitialized (contains previously stored value) ❖ Initialization Hint ‣ At declaration = does not mean equal. int a=0; int a=0, b=1; a = 5 means store 5 in the variable called a. ‣ Assignment int a; int a, b; int a, b; Hint a=0; a=0; a=b=0; Initialize or assign b=1; value to a variable ❖ Printing: same as constants before using its contents. printf("%d", year); Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 13 Quiz

❖ What’s printed? #include quiz.c int main() { int a=0, b, c, d, e, f; b=1; c=d=2; printf("a=%d\n", a); a=0

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

printf("c=%d\n", c); c=2

printf("d=%d\n", d); d=2

printf("e=%d\n", e); e=589 Or whatever stored before

printf("f=%d\n", f); f=-2381039 Likewise return 0; }

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 14 Reading Integers

❖ scanf() with %d (or %i)

#include scanf1.c int main() { int myvar; printf("Type an integer: "); scanf("%d", &myvar); printf("It is: %d\n", myvar); return 0; }

Always (for now..) use scanf with & - stores value in that location Think of &myvar as the address of myvar More later

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 15 Non-Integer Input

%d skips initial white space (space, tab, newline) Then reads till first non-integer character #include scanf1.c int main() { int value; Preceding printf("Type an integer: "); white space scanf("%d", &value); printf(“You typed %d\n", value); ignored } return 0;

15 You typed 15 15 You typed 15

1b 1.5 1+234 You typed 1 rest left for future scanf’s

b < .5 You typed -183793 whatever stored before

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

#include scanf2.c int main() { int value1, value2; printf("Now gimme two: "); scanf("%d%d", &value1, &value2); printf("Their sum: %d\n", value1+value2); return 0; }

❖ Spaces preceding %d don’t matter (as skips initial spaces) same scanf(" %d %d", &value1, &value2);

❖ Spaces following last %d may matter (later)

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 17 Maximum Field Size

Integer between % and d specifies maximum # digits read

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

123 a=12

scanf("%1d%d", &a, &b); 123 a=1 b=23

same

scanf("%1d", &a); 123 a=1 b=23 scanf("%d", &b);

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

❖ Non % text is expected and must appear scanf("%d,%d", &a, &b); 1,2 a=1 b=2 Remember mainly this scanf("%dxy%d", &a, &b); 1xy2 a=1 b=2 part! ❖ ALLOWED modifications Keep rest in ‣ %d skips initial space, so space after separator ok mind, but scanf("%d,%d", &a, &b); 1, 2 a=1 b=2 less likely to scanf("%dxy%d", &a, &b); 1xy 2 a=1 b=2 be in exams. ‣ Format space means >=0 spaces, so remove/add space ok scanf("%d x y %d", &a, &b); 1 x y 2 a=1 b=2

❖ DISALLOWED 1 xy2 a=1 b=2 separator.c ‣ Add space before separator scanf("%d,%d", &a, &b); 1 ,2 a=1 b=#&<) scanf("%dxy%d", &a, &b); 1 xy2 a=1 b= time.c 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; }

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 20 How Many Values scanf Read?

❖ Returns # of successfully read variables #include scanf_num.c 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; } Try entering 5a

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 21 Using # Values scanf Read

❖ Calculate average of up to 4 integers #include average.c 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!!

❖ Later - better ways of doing that

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 22 Can we Print Everything?

Means How to print? Like so

” end format ” \”

\n newline \ \\

%d decimal % %%

printf(“\””); ” printf(“\\\\”); \\

printf(“\\n”); \n

printf(“%%d”); %d

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 23 ❖ 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

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 24 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 ‣ Always start with 0 Though not on exam, ‣ With n bits, represent 0 to 2n-1-1 you should know this!

❖ 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 Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 25 Size of int

❖ Standards don’t determine size of int ❖ Most compilers allocate 4 bytes (32 bits) byte = 8 bits ❖ Range: -231,…,-1,0,1,…,231-1 31 ❖ 2 = 2,147,483,648 ~ 2 Billion 10 1,024 2 ~thousand #include int main() { 220 1,048,567 ~million int x=2147483647; 230 1,073,741,824 ~billion printf("x=%d\n", x); printf("x+1=%d\n", x+1); return 0; > a.out } largest_int.c x=2147483647 x+1=-2147483648 ❖ Often not enough > ❖ How do we know # bytes? Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 26 sizeof ❖ sizeof(object) returns # bytes used to store object ❖ object: ‣ Type name: int ‣ Variable name: x ‣ Expression: 3*x+5 printf("Number of bytes:\n"); sizeof1.c 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: ❖ Shortly use for other types int: 4 dummy: 4 3*dummy: 4

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 27 Other Integer Types ❖ short, long (often = int), long long (large integers) ‣ Sizes guaranteed to satisfy sizeof(short)≤sizeof(int)≤ sizeof(long)≤ sizeof(long long)

printf("short: %lu, int: %lu, \ Line continues 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

short: 2, int: 4, long int: 8, long long int: 8 dummy: 8, 3*dummy: 8

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 28 Reading & Writing Integer Types

❖ Constants Needed only for really long integers ‣ long - 35L, long long - 21537LL ❖ printf and scanf ‣ short - %hd, long - %ld, long long - %lld sizeOfTypes2.c #include Largest int: int main() { 2147483647 long int a ü= 5, b ü= 5L; int c ✘= 2147483648, d ✘= 2147483648L; long int e ü= 2147483648L; long long int f=ü2147483648LL; printf("a=%ld b=%ld e=%lld f=%lld\n", a,b,h,h); return 0; } Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 29 Unsigned

❖ unsigned represents only positive integers, hence doubles the range. For example, if int occupies 4 bytes int: -231,…,-2,-1,0,1,2,…,231-1 unsigned int: 0,1,2,…,232-1 ❖ Similarly: unsigned char, unsigned short, unsigned long

#include needed only when large unsigned.c int main() { unsigned int us1 = 5u, us2 = 5U, us3 = 5; printf("us1=%d us2=%u us3=%U\n, us1,us2,us3); return 0; }

❖ Same for scanf

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 30 Octal and Hexadecimal Constants ❖ Constants ‣ Octal - precede with 0 (zero) printf("%d", 012); 10 ‣ Hexadecimal - precede with 0x printf("%d", 0x12); 18 ❖ Printing ‣ Octal (%o) printf("%o", 13); 15 ‣ Hexadecimal (%x,%X) printf("%x", 13); d

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 31 Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 32 Constants

❖ Floating point 1.23 0.7 .7 +13.0 -13.

❖ Scientific notation 1.23e1 .123E+2 =.123*102 = 12.3

❖ Integers (converted) 13 Caution when printing integer as float

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 33 Printing

❖ Print: %g, %lf, %f, or %e

printf("%g", 24.00); 24 scientific notation .174e2=.174*102

printf("%g", .174e2); 17.4 gcc -Wall alerts to problem printf("%g", 7);û -3.23732e-232 by default 6 printf("%f", 2.4); 2.400000 digits after point 2 digits after point printf("%.2f", 2.4); 2.40 print total of at least 6 digits including point printf("#%-6.2f#", 2.4); #2.40 # - left justify printf("%e", -24.); -2.400000e+01

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 34 float and double ❖ Basic types, double provides more precision, more common ❖ Constants are double ❖ Declaration double fraction; float width, height; ❖ Uninitialized (contains previously stored value) ❖ Initialization ‣ At declaration float a=0.5; double a=5, b=3e-2; ‣ Assignment double a; double a, b; a=.13; a=b=-17.23; ❖ Printing: same as constants (for both double and float) printf("%f", width); Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 35 Reading ❖ scanf() with %f (float), %lf (double)

#include int main() { Again! double x; printf("Real #: "); scanf("%lf", &x); printf("Typed: %g\n", x); return 0; } ❖ Reading & writing mixed types int i; double x; float y; mix.c printf("Enter int, double, and float: "); scanf("%d%lf%f", &i, &x, &y);

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

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 36 Representation Represented by binary floating-point expansion

sign exponent mantissa

3.1415926 11.001001000011111

0|10|11001001000011111 You should know, but not in exams.

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

Other reals are approximated

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 37 Other Real-Valued Data Types

❖ In addition to double and float can use long double ❖ Standard guarantees sizeof(float) ≤ sizeof(double) ≤ sizeof(long double) ❖ 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

sizeofFloatingPoint.c

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 38 Characters

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 39 char

❖ Constants Forward ‣ Enclosed in ‘ ‘: 'a', 'Z', '3', '+', '#', '$' ‣ Some letters cannot be written directly, use escape: \ '\n'-- newline '\t'-- tab '\b'-- backspace '\a' -- bell (alert) moves back, ❖ Declaration doesn’t erase char letter_name; char letter_name, initial; ❖ Uninitialized (contains previously stored value) ❖ Initialization char a; char a, b; char a=’d’; a=’#’; a=b=’\b’;

‣ Wrong: char a=d;çThinks it’s a variable

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 40 Printing and Reading

❖ Printing printf("%c", ’d’); same as printf("d"); char vowel=’H’; printf("%ca%c", vowel, ’!’); Ha!

printf("%c%c%c", ’a’,’\b’,’b’); b printf("%c%c%c%c", ’a’,’\b’,’b’,’\b’); b printf("%c%c%c%c",’\a’,’\a’,’\a’,’\a’); ❖ Reading Assume: char a1, a2;

scanf("%c", &a1); again char.c scanf("%c%c", &a1, &a2); nt ten Lectureprintf( 2 "%ce%c\n" ECE15: Introduction to ,Computer a2, Programming a1); Using the C Language 41 Representation ❖ Character stored in one byte (8 bits)

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

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

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 42 ASCII Table FreeFree ASCII ASCII ChartFree ChartFree ASCII ASCII Chart Chart

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0 ... 7 ... 48 49 ... 65 66 ... 97 98 ... 127 \0 ... \a ... 0 1 ... A B ... a b ... DEL ❖ Can (not recommended) use numbers instead of characters char let = ’b’; same as char let = 98;

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

printf("%d", let); 98 printf("%c", let); b

❖ Can add and subtract

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

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

bell.c

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 44 Quiz

❖ What does the following program do? #include int main() { -32 char c; printf("Lower case letter: "); + 66 - 97 scanf("%c", &c); printf("I druther type: %c\n", c + ’A’ - ’a’); return 0; lower case to } UPPER what.c

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

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 45 Skipping White Space

❖ %d reads integers, skips white space ❖ %c reads characters, doesn’t skip anything ❖ What if scanf %d followed by %c printf("Number: "); skipWhite.c > a.out scanf("%d", &num); Number: 57 printf("Letter: "); Letter: 57 scanf("%c", &let); printf("%d %c\n", num, let); > ‣ Newline after int is not be read by %d, read as char ❖ To skip white spaces before char, use " %c" scanf(" %c", &let); > a.out or Number: 57 Letter: c scanf("%d %c", &num, &let); 57 c > Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 46 Skipping Specific Input

❖ To skip specific input use * ❖ %*d skips an integer scanf("%*d"); ❖ To skip specific values (at least one): scanf("%*[ \t\n]");

Read three integers, Read integer, skip white spaces print first and last and b’s, and read character

#include #include int main() { int main() { int i, j; int i; char c; printf("Three ints: "); printf("Intchar: "); scanf("%d%*d%d", &i, &j); scanf("%d%*[b \t\n]%c",&i,&c); printf("i=%d j=%d\n",i,j); printf("i=%d c=%c\n",i,c); return 0; return 0; } skip_int.c } skip_b_white.c

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 47 getchar() and putchar()

❖ Simple way of reading and writing single characters #include int main() { char a, b; a=getchar(); b=getchar(); putchar(b); putchar(a); return 0; } getputchar.c ❖ Useful for pausing programs Especially demos...

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 48 Strings

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 49 Strings

❖ Sequence of characters enclosed in quotes

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

❖ 'a' and "a" stored differently (more when study arrays) ❖ Printing printf("hello"); same as printf("%s", "hello"); hello

int a=1, b=2; printf("%d+%d%s%d\n", a, b, " equals ", a+b); 1+2 equals 3

printf("\a"); printf("\b "); space, so overwrites ❖ Reading: when study arrays (need to allocate space)

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 50 File Input and Output

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 51 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): > m InFile ‣ a.out < file1 input read from file1 > 7 11 a.out < InFile ‣ a.out > file2 output printed to file2 1st: 7 2nd: 11 All input from all output to > m OutFile ❖ file1 file2 OutFile: No such file.. (none from keyboard / to screen) a.out > OutFile 20 #include inOut.c 11 > m OutFile int main() { 1st: 20 int x, y; 2nd: 11 > a.out OutFile scanf("%d %d", &x, &y); > m OutFile printf("1st: %d\n2nd: %d\n", x,y); 1st: 7 2nd: 11 return 0; } >

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 52 Outline ❖ Writing

❖ Reading

❖ Variables and data types ‣ Text ‣ Integers ‣ Reals ‣ Characters ‣ Strings ❖ Rudimentary file input/output

Lecture 5 ECE15: Introduction to Computer Programming Using the C Language 53 Who gets?

❖ Most

❖ Some

❖ None

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 54 Where are we?

❖ Two weeks old ❖ Already can read & write! ❖ What’s next?

Lecture 2 ECE15: Introduction to Computer Programming Using the C Language 55