270_1_CIntro_Up_To_Functions.ppt 0478 computer

CSC 270 – Survey of
Programming Languages
C Lecture 1 : Getting Started: in C
Modified from Dr. Robert Siegfried’s Presentation

Objective
• Intro to C
• Tools we will use
• Program file structure
• Variables
• Read from screen and print to screen
• Decisions (If)

C Orientation
• Created in 1972 to write operating systems (Unix in
particular)
– By Dennis Ritchie
– Bell Labs
• Evolved from B
• Can be portable to other hardware (with careful
design – use Plauger’s The Standard C Library
book)
• Built for performance and memory management –
operating systems, embedded systems, real-time
systems, communication systems

C Standardization
• 1989 ANSI and ISO -> Standard C
• 1999 C99
• 2011 C11
• Don’t get thrown when you lookup
information on websites and find conflicts
based upon standards

Later Languages
• 1979 C++ by Bjarn Stroustrup also at Bell
– Object orientation
• 1991 Java by Sun
– Partial compile to java bytecode: virtual machine
code
– Write once, run anywhere
– Memory manager – garbage collection
– Many JVMs written in C / C++

A First Program
#include <stdio.h>
int main(void)
{
printf("This is my first C program.n");
return(0);
}
statements
header
open and close braces mark
the beginning and end
makes input
and output available
to us

A First Program – What Does It Do?
printf("This is my first C program.n");
return(0);
Prints the message
This is my first C program.
Ends the program Ends the line

Java Reminder
Program C Java
hello, world
#include<stdio.h> public class HelloWorld {
int main(void) {
public static void main(String[]
args) {
printf("Hellon"); System.out.println("Hello");
return 0; }
} }

C Program Phases
• Editor - code by programmer
• Compiling using gcc:
– Preprocess – expand the programmer’s code
– Compiler – create machine code for each file
– Linker – links with libraries and all compiled
objects to make executable
• Running the executable:
– Loader – puts the program in memory to run it
– CPU – runs the program instructions

Copyright © Pearson, Inc. 2013. All Rights
Reserved.

Run First Program
• Write in notepad++
• Transfer with Filezilla
• Connect to panther as terminal (putty) using
SSH (Secure Shell)
• More filename to see the file
• gcc filename -o filename without c -g (ex: gcc
hello.c -o hello -g )
• ./hello

Using variables
#include <stdio.h>
int main(void)
{
int sum, value1, value2, value3;
float average;
value1 = 2;
value2 = 4;
value3 = 6;
sum = 2 + 4 + 6;
average = sum / 3;
printf("The average of %d , %d, %d is %fn", value1,
value2, value3, average);
return(0);
}
Print a float value from the
rest of the parameter list

Variables and Identifiers
• Variables have names – we call these names identifiers.
• An identifier must begin with a letter or an underscore _
• C is case sensitive upper case (capital) or lower case letters
are considered different characters. Average, average
and AVERAGE are three different identifiers.
• Numbers can also appear after the first character.
• However, C only considers the first 31 (external
identifiers) or first 63 (internal identifiers) significant.
• Identifiers cannot be reserved words (special words like
int, main, etc.)

User Input
• Let’s rewrite the average program so it
can find the average any 3 numbers we
try:
• We now need to:
1. Find our three values
2. Add the values
3. Divide the sum by 3
4. Print the result

Average3.c
#include <stdio.h>
int main(void)
{
int value1, value2, value3;
float sum, average;
printf("What is the first value? ");
scanf("%d", &value1);
printf("What is the second value? ");
Indicates that we are
reading an integer
Read The address of variable value1

printf("What is the third value? ");
sum = value1 + value2 + value3;
average = sum / 3;
printf("The average of %d , %d, %d is %f
n", value1, value2, value3, average);
return(0);
}
scanf needs the &
before the identifier

Scanf Conversion Characters
• https://wpollock.com/CPlus/
PrintfRef.htm#scanfConv
Doubles on our machine are read with a lf.
(A double is a long float.)

Formatting %d and %f
• The specifiers %d and %f allow a programmer to
specify how many spaces a number will occupy and
how many decimal places will be used.
• %nd will use at least n spaces to display the integer
value in decimal (base 10) format.
• %w.nf will use at least w spaces to display the value
and will have exactly n decimal places.
• Example:
– printf("The average of %2d , %2d, %2d
is %5.2fn", value1, value2, value3,
average);

Changing the width
```-182
%7d
-182
`-182
%5d
-182
-182
%4d
-182
`’’`182
%7d
182
``182
%5d
182
182
%3d
182
182
%2d
182
Print as:
Formatting
Number

Changing the width (continued)
….-11023
%10d
-11023
-11023
%6d
-11023
.11023
%6d
11023
11023
%4d
11023
……23
%8d
23
….23
%6d
23
23
%2d
23
23
%1d
23
Print as:
Formatting
Number

Changing The Precision
Number Formatting Prints as:
2.718281828 %8.5f `2.71828
2.718281828 %8.3f ```2.718
2.718281828 %8.2f ````2.72
2.718281828 %8.0f ````````3
2.718281828 %13.11f 2.71828182800
2.718281828 %13.12f 2.718281828000

Average – add comments
#include <stdio.h>
/*
* This program calculates average pay
*/
int main(void)
{
int value1, value2, value3;
float sum, average;
string
// now get the first value
;
comments

Character Data
• All of our programs so far have used variables
to store numbers, not words.
• We can store one or more characters by
writing:
char x, s[10];
– x can hold one and only one character
– s can hold up to nine characters (reserving 1 for
ending null)
• For now, we use character data for input and
output only.

A program that uses a character variable
#include <stdio.h>
/* A very polite program that greets you by name */
int main(void)
{
char name[25];
/* Ask the user his/her name */
printf("What is your name ? ");
scanf("%s", name);
/* Greet the user */
printf("Glad to meet you, %sn.", name);
return(0);
}

Features so far
• Include
• Variable types: int, float, char
• Read using scanf
– requires & for address of variable being read
• Print using printf
• Format strings: %f (float), %d (int), %u
(unsigned int), %c (char), %s (character array)
• Comments /*.. */ or //

if and if-else and if-else if - else
If (boolean_expression 1)
{ /statements }
else if ( boolean_expression 2)
{ /* statements */ }
else if ( boolean_expression 3)
else

IsItNeg.c – illustrate if
#include <stdio.h>
// Tell a user if a number is negative
int main(void)
{ float number;
/* Ask the user for a number */
printf("Please enter a number ? ");
scanf("%f", &number);
// Print whether the number is negative or not
if (number < 0){
printf("%f is a negative numbern", number); }
else {
printf("%f is NOT a negative numbern", number); }
return(0); }

Relational operators
Operator Meaning Example
== equals x == y
!= is not equal to 1 != 0
> greater than x+1 > y
< less than x-1 < 2*x
>= greater than or
equal to
x+1 >= 0
<= less than or equal
to
-x +7 <= 10

Integer Division
• Our compound interest program prints the
values for every year where every ten or
twenty years would be good enough.
• What we really want to print the results
only if the year is ends in a 5. (The
remainder from division by 10 is 5).

Integer Division Results
8 / 3 = 2 8 % 3 = 2
2 / 3 = 0 2 % 3 = 2
49 / 3 = 16 49 % 3 = 1
49 / 7 = 7 49 % 7 = 0
‑8 / 3 = 2
‑ ‑8 % 3 = 2
‑
‑2 / 3 = 0 ‑2 % 3 = 2
‑
‑2 / 3 = 0
‑ ‑2 % 3 = 2
‑ ‑
2 / 3 = 0
‑ 2 % 3 = 2
‑
‑49 / 3 = 16
‑ ‑49 % 3 = 1
‑

Choosing Data Types
• Sizes implementation dependent in limits.h
– int -2147483648 to 2147483647
– short -32768 to 32767
– long -9223372036854775808 to
9223372036854775807
– Float 1.17x10-38
to 3.4 * 1038
• Keyword unsigned starts at 0 but goes
higher

Declaring Constants
•There are two ways of defining constants in C: using
#define and const.
•#define is a compiler preprocessor which replaces each
occurrence of the constant's name with its value:
•The general form of the constant declaration is:
#define ConstantName ConstantValue
•Let's take a look at a few examples:
#define withholding_rate 0.8
#define prompt 'y'
#define answer "yes"
#define maxpeople 15
#define inchperft 12
#define speed_limit 55

Declaring Constants
•The general form of the constant declaration is:
const datatype ConstantName =
ConstantValue,
AnotherConstantName =
AnotherConstantValue;
•Let's take a look at a few examples of constants:
const float withholding_rate = 0.8;
const char prompt = ‘y‘,
answer[] = “yes”;
const int maxpeople = 15,
inchperft = 12;
speed_limit = 55;

Java Comparison Thus Far
Feature C Java
type of language function oriented / imperative object oriented
file naming
conventions
stack.c, stack.h
Stack.java - file name matches
name of class
basic programming
unit
function class / Abstract Data Type
portability of source
code
possible with discipline yes
portability of
compiled code
no, recompile for each architecture
yes, bytecode is "write once, run
anywhere"
compilation
gcc hello.c creates machine
language code
javac Hello.java creates Java
virtual machine language
bytecode
buffer overflow
segmentation fault, core dump,
unpredicatable program
checked run-time error exception
boolean type
use int: 0 for false, nonzero for
true OR include <stdbool.h> and
use bool
boolean is its own type - stores
value true or false
character type char is usually 8 bit ASCII char is 16 bit UNICODE
strings '0'-terminated character array
built-in immutable String data
type
accessing a library #include <stdio.h> import java.io.File;

More Java Comparison
Feature C Java
printing to standard
output
printf("sum = %d", x); System.out.println("sum = " + x);
formatted printing printf("avg = %3.2f", avg);
System.out.printf("avg = %3.2f",
avg)
reading from stdin scanf("%d", &x); int x = StdIn.readInt();
declaring constants const and #define final
for loops for (i = 0; i < N; i++) for (int i = 0; i < N; i++)
variable auto-
initialization
not guaranteed
instance variables (and array
elements) initialized to 0, null, or
false, compile-time error to access
uninitialized variables
casting anything goes
checked exception at run-time or
compile-time
demotions automatic, but might lose precision
must explicitly cast, e.g., to convert
from long to int
variable declaration at beginning of a block before you use it
variable naming
conventions
sum_of_squares sumOfSquares
Credit: http://introcs.cs.princeton.edu/java/faq/c2java.html

Summary
• Tools we will use
– Notepad++
– Filezilla
– Panther (gcc)
– Putty
• Program file structure
– #include <> or “ “
– Main function

Summary Cont.
• Variables
– int, float, char
– unsigned keyword
– String defined as char array : char name[26]
– For bool, include stdbool.h
– Constant:
• #define name value
• const type name = ?
– Get address of variable with &
– Cast with (type) var
•

Summary Cont.
•Read from screen and print to screen
– Scanf (control string, variable addresses)
– Printf(string, variables to insert)
– Format strings %2f, %d, %s, %u
– #include <stdio.h>
•Decisions
– If / else if / else

Exercise
• https://prof.beuth-hochschule.de/fileadmin/
user/scheffler/Lehre/Think-C_v1.08.pdf
• Exercise 2.1

270_1_CIntro_Up_To_Functions.ppt 0478 computer

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