Programming in C Basics

C programming---basic
1 Introduction to C
2 C Fundamentals
3 Formatted Input/Output
4 Expression
5 Selection Statement
6 Loops
7 Basic Types
8 Arrays
9 Functions
10 Pointers
11 Pointers and Arrays

Introduction to C
Intended use and underlying philosophy
1 C is a low-level language
---suitable language for systems programming
2 C is a small language
---relies on a “library” of standard functions
3 C is a permissive language
---it assumes that you know what you’re doing, so it allows
you a wider degree of latitude than many languages. It
doesn’t mandate the detailed error-checking found in
other language

Introduction to C
Strengths:
+ Efficiency: intended for applications where assembly language
had traditionally been used.
+ Portability: hasn’t splintered into incompatible dialects; small
and easily written
+ Power: large collection of data types and operators
+ Flexibility: not only for system but also for embedded system
commercial data processing
+ Standard library
+ Integration with UNIX

Introduction to C
Weaknesses:
+ error-prone
+ difficult to understand
+ difficult to modify

Similarities of C to java
•/* Comments */
•Variable declarations
•if / else statements
•for loops
•while loops
•function definitions (like methods)
•Main function starts program

Differences between C and java
•C does not have objects
There are “struct”ures
•C is a functional programming language
•C allows pointer manipulation
•Input / Output with C
Output with printf function
Input with scanf function

C Fundamentals
First program
#include <stdio.h>
main()
{
printf(“To C, or not to C: that is the question”);
}

C Fundamentals
Compiling and Linking
Preprocessing: the program is given to a preprocessor,
which obeys commands that begin with #(directives)
add things to the program and make modifications
Compiling: modified programcompilerobject
code
Linking: add library functions to yield a complete
executable program

C Fundamentals
Compiler
% cc –o pun pun.c
% gcc –Wall –o pun pun.c

C Fundamentals
Keywords
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while

Variable Type
C has the following simple data types:

Variable Type
Java has the following simple data types:

Basic Types
Type (16 bit) Smallest Value Largest Value
short int -32,768(-215) 32,767(215-1)
unsigned short int 0 65,535(216-1)
Int -32,768 32,767
unsigned int 0 65,535
long int -2,147,483,648(-231) 2,147,483,648(231-1)
unsigned long int 0 4,294,967,295

Basic Types
Type (32 bit) Smallest Value Largest Value
short int -32,768(-215) 32,767(215-1)
unsigned short int 0 65,535(216-1)
Int -2,147,483,648(-231) 2,147,483,648(231-1)
unsigned int 0 4,294,967,295
long int -2,147,483,648(-231) 2,147,483,648(231-1)
unsigned long int 0 4,294,967,295

Data Types
• char, int, float, double
• long int (long), short int (short),
long double
• signed char, signed int
• unsigned char, unsigned int
•1234L is long integer
•1234 is integer
•12.34 is float
•12.34L is long float

Reading and Writing Integers
unsigned int u;
scanf(“%u”, &u); /* reads u in base 10 */
printf(“%u”, u); /* writes u in base 10 */
scanf(“%o”, &u); /* reads u in base 8 */
printf(“%o”, u); /* writes u in base 8 */
scanf(“%x”, &u); /* reads u in base 16 */
printf(“%x”, u); /* writes u in base 16*/
short int x;
scanf(“%hd”, &x);
printf(“%hd”, x);
long int x;
scanf(“%ld”, &x);
printf(“%ld”, x);

Floating Types
float single-precision floating-point
double double-precision floating-point
long double extended-precision floating-point
Type Smallest
Positive Value
Largest Value Precision
float 1.17*10-38 3.40*1038 6 digits
double 2.22*10-308 1.79*10308 15 digits
double x; long double x;
scanf(“%lf”, &x); scanf(“%Lf”, &x);
printf(“%lf”, x); printf(“%Lf”, x);

Character Types
char ch;
int i;
i = ‘a’; /* i is now 97 */
ch = 65; /* ch is now ‘A’ */
ch = ch + 1; /* ch is now ‘B’ */
ch++; /* ch is now ‘C’ */
if(‘a’ <= ch && ch <= ‘z’)
for(ch = ‘A’; ch <= ‘Z’; ch++)

Char Type
‘a‘, ‘t’, ‘n’, ‘0’, etc. are character
constants
strings: character arrays
− (see <string.h> for string functions)
− "I am a string"
− always null (‘0’) terminated.
− 'x' is different from "x"

Type Conversion
narrower types are converted into
wider types
− f + i int i converted to
characters <---> integers
<ctype.h> library contains
conversion functions, e.g:
− tolower(c) isdigit(c) etc.
Boolean values:
− true : >= 1 false: 0

Type Conversion
long double
double
float
Unsigned long int
long int
unsigned int
int

Type Conversion
char c;
short int s;
int i;
unsigned int u;
long int l;
unsigned long int ul;
float f;
double d;
long double ld;
i = i + c; /* c is converted to int */
i = i + s; /* s is converted to int */
u = u +i; /* i is converted to unsigned int */
l = l + u; /* u is converted to long int */
ul =ul + l; /* l is converted to unsigned long int */
f = f + ul; /* ul is converted to float */
d = d + f; /* f is converted to double */
ld = ld + d; /* d is converted to long double */

Casting
( type-name ) expression
float f, frac_part;
frac_part = f – (int) f;
float quotient;
int dividend, divisor;
quotient = (float) dividend / divisor;
short int i;
int j = 1000;
i = j * j; /* WRONG */

Type Definitions
typedef int BOOL
BOOL flag; /* same as int flag; */
typedef short int Int16
typedef long int Int32
typedef unsigned char Byte
typedef struct {int age; char *name} person;
person people;

Formatted Input/Output
printf function
printf(string, expr1, expr2, ……..)
string: ordinary characters and conversion
specifications (%)
%d --- int %s --- string %f --- float
printf(“i=%d, j=%d. x=%fn”, i, j, x);

Conversion Specification
%[-]m.pX
m: specifies the minimum number of characters to print.
%4d-- _123; %-4--123_
p: depends on the choice of X
X:
-d: decimal form
-e: floating-point number in exponential format
-f: floating-point number in “fixed decimal” format
-g: either exponential format or fixed decimal format,
depending on the number’s size

main()
{
int i = 40;
float x = 839.21;
printf(“|%d|%5d|%-5d|%5.3d|n”, i, i, i, i);
printf(“|%10.3f|%10.3e|%-10g|n”, x, x, x);
}

Escape Sequence
Enable strings to contain characters that would otherwise cause
problems for the compiler
alert a new line n ” “
backspace b horizontal tab t

How scanf works: is controlled by the conversion specification
In the format string starting from left to right.
When called, it tries to locate an item of the appropriate type
In the input data, skipping white-space characters(the space,
Horizontal and vertical tab, form-feed, and new-line character)
scanf(“%d%d%f%f”, &i, &j, &x, &y);
input:
___1
-20___.3
___-4.0e3
___1*-20___.3*___-4.0e3*
sss r s rrr sss rrs sss rrrrrr

Ordinary Characters in Format
String
White-space characters: one white-space character in
the format string will match any number of white-space
character in the input.
Other characters: when it encounters a non-white-space
character in a format string, scanf compares it with the
next input character. If the two characters match, scanf
discards the input character and continues processing
the format string. Otherwise, scanf puts the offending
character back into the input, then aborts without futher
processing.
%d/%d will match _5/_96, but not _5_/_96
%d_/%d will match _5_/_96

Expressions
Arithmetic operator: +, -, *, /, %, ++, --………
Relational operator: <, >, <=, >=, !=
Logical operator: &&, ||

Operator Precedence and Associativity
highest: + - (unary)
* / %
lowest: + - (binary)
-i * -j = (-i) * (-j)
+i + j / k = (+i) + (j / k)
left/right associative: it groups from left/right to right/left
The binary arithmetic operators (*, /, %, + and -) are all left associative
i – j – k = (i – j) – k i * j / k = (i * j) / k
The unary arithmetic operators( + and -) are both right associative
- + i = - ( +i )

Expression Evaluation
Precedence Name Symbol(s) Associativity
1 X++/X-- left
2 ++X/--X
unary +/-
right
3 multiplicative *, /, % left
4 additive +, - left
5 assignment =, *=, /=, +=, -= right

Expression Evaluation
a = b += c++ - d + --e / -f
a = b += (c++) - d + --e / -f
a = b += (c++) - d + (--e) / -f
a = b += (c++) - d + (--e) / (-f)
a = b += (c++) - d + ((--e) / (-f))
a = b += ((c++) – d) + ((--e) / (-f))
a = b += (((c++) – d) + ((--e) / (-f)))
a = (b += (((c++) – d) + ((--e) / (-f))))
(a = (b += (((c++) – d) + ((--e) / (-f)))))

Bitwise Operations
• Applied to char, int, short, long
– And &
– Or |
– Exclusive Or ^
– Left-shift <<
– Right-shift >>
– one's complement ~

Example: Bit Count
/*
count the 1 bits in a number
e.g. bitcount(0x45) (01000101 binary) returns 3
*/
int bitcount (unsigned int x) {
int b;
for (b=0; x != 0; x = x >> 1)
if (x & 01) /* octal 1 = 000000001 */
b++;
return b;
}

Conditional Expressions
• Conditional expressions
• expr1? expr2:expr3;
• if expr1 is true then expr2 else expr3
for (i=0; i<n; i++)
printf("%6d %c",a[i],(i%10==9||i==(n-1))?'n':' ');

Control Flow
• blocks: { ... }
• if (expr) stmt;
• if (expr) stmt1 else stmt2;
• switch (expr) {case ... default }
• while (expr) stmt;
• for (expr1;expr2;expr3) stmt;
• do stmt while expr;
• break; continue (only for loops);
• goto label;

Scope Rules
• Automatic/Local Variables
– Declared at the beginning of functions
– Scope is the function body
• External/Global Variables
– Declared outside functions
– Scope is from the point where they are declared
until end of file (unless prefixed by extern)

Scope Rules
• Variables can be declared within blocks too
– scope is until end of the block
{
int block_variable;
}
block_variable = 9; (wrong)

Scope Rules
• Static Variables: use static prefix on functions
and variable declarations to limit scope
– static prefix on external variables will limit scope
to the rest of the source file (not accessible in
other files)
– static prefix on functions will make them invisible
to other files
– static prefix on internal variables will create
permanent private storage; retained even upon
function exit

Hello, World
#include <stdio.h>
/* Standard I/O library */
/* Function main with no arguments */
int main () {
/* call to printf function */
printf("Hello, World!n");
/* return SUCCESS = 1 */
return 1;
}
% gcc -o hello hello.c
% hello
Hello, World!
%

Celsius vs Fahrenheit table
(in steps of 20F)
• C = (5/9)*(F-32);
#include <stdio.h>
int main() {
int fahr, celsius, lower, upper, step;
lower = 0;
upper = 300;
step = 20;
fahr = lower;
while (fahr <= upper) {
celsius = 5 * (fahr - 32) / 9;
printf("%dt%dn",fahr, celsius);
fahr += step;
}
return 1;
}

Celsius vs Fahrenheit table
Remarks
• 5/9 = 0
• Primitive data types: int, float, char, short,
long, double
• Integer arithmetic: 0F = 17C instead of 17.8C
• %d, %3d, %6d etc for formatting integers
• n newline
• t tab

New Version Using Float
#include <stdio.h>
int main() {
float fahr, celsius;
int lower, upper, step;
lower = 0;
upper = 300;
step = 20;
fahr = lower;
while (fahr <= upper) {
celsius = (5.0 / 9.0) * (fahr - 32.0);
printf("%3.0f %6.1f n", fahr, celsius);
fahr += step;
}
return 1;
}

New Version Using Float
Remarks
• %6.2f 6 wide; 2 after decimal
• 5.0/9.0 = 0.555556
• Float has 32 bits
• Double has 64 bits
• Long Double has 80 to 128 bits
– Depends on computer

Version 3 with “for” loop
#include <stdio.h>
int main() {
int fahr;
for (fahr=0; fahr <= 300; fahr += 20)
printf("%3d %6.1f n", fahr,
(5.0 / 9.0) * (fahr – 32.0));
return 1;
}

Version 4 with Symbolic Constants
#include <stdio.h>
#define LOWER 0
#define UPPER 300
#define STEP 20
int main() {
int fahr;
for (fahr=LOWER; fahr <= UPPER; fahr += STEP)
printf("%3d %6.1f n", fahr,
(5.0 / 9.0) * (fahr - 32.0));
return 1;
}

Character I/O
• c = getchar();
• putchar(c);
Coyp file
#include <stdio.h>
int main() {
char c;
c = getchar();
while (c != EOF) {
putchar(c);
c = getchar();
}
return 0;
}

File Copying (Simpler Version)
• c= getchar() != 0 is equivalent to
c = (getchar() != EOF)
• Results in c value of 0 (false) or 1 (true)
#include <stdio.h>
int main() {
int c;
c = getchar();
while ((c = getchar())!= EOF)
putchar(c);
return 0;
}

Counting Characters
• Remarks: nc++, ++nc, --nc, nc--
• %ld for long integer
#include <stdio.h>
int main () {
long nc = 0;
while (getchar() != EOF)
nc++;
printf("%ldn",nc);
}
#include <stdio.h>
int main () {
long nc;
for (nc=0;getchar() != EOF;nc++);
printf("%ldn",nc);
}

Counting Lines
#include <stdio.h>
int main () {
int c, nl=0;
while ((c = getchar()) != ‘Z’)
if (c == 'n')
nl++;
printf("%dn",nl);
}

Counting Words
#include <stdio.h>
#define IN 1
#define OUT 0
int main () {
int c, nl, nw, nc, state;
state = OUT;
nl = nw = nc = 0;
while ((c = getchar()) != ‘Z’) {
++nc;
if (c == 'n')
nl++;
if (c == ' ' || c == 'n' || c == 't')
state = OUT;
else if (state == OUT) {
state = IN;
++nw;
}
}
printf("%d %d %dn",nc, nw, nl); }

Notes about Word Count
• Short-circuit evaluation of || and &&
• nw++ at the beginning of a word
• use state variable to indicate inside or outside
a word

Programming in C Basics

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