Cse115 lecture04introtoc programming

Lecture 04
Introduction to C Programming
CSE115: Computing Concepts

preprocessor directives
main function heading
{
declarations
executable statements
}
General Form of a C Program

A Simple Program in C
#include <stdio.h>
#include <stdlib.h>
int main()
{
printf("Hello world!n");
return 0;
}

A Simple Program in C
#include <stdio.h>
#include <stdlib.h>
int main()
{
printf("Hello world!n");
return 0;
}
standard Library, input-output, header-file
Beginning of program
End of Segment
Start of Segment
Function for printing text
End of statement
Insert a new line

Preprocessor Directives
• A C program begins with # which provides an instruction to the C
preprocessor
• It is executed before the actual compilation is done.
• Two most common directives :
• #include
• #define
• In our example (#include<stdio.h>) identifies the header
file for standard input and output operations.

Function main()
• Identify the start of the program
• Every C program has a main( )
• 'main' is a C keyword. We must not use it for any other
purpose.
• 4 common ways of main declaration
int main(void)
{
return 0;
}
void main(void)
{
}
main(void)
{
}
main( )
{
}

The curly braces { }
• Identify a segment / body of a program
• The start and end of a function
• The start and end of the selection or repetition block.
• Since the opening brace indicates the start of a segment
with the closing brace indicating the end of a segment,
there must be just as many opening braces as closing
braces (this is a common mistake of beginners)

Statement
• Specifying an action to be taken by the computer as the program
executes.
• Each statement in C needs to be terminated with semicolon (;)
• Example:
#include <stdio.h>
int main()
{
printf(“I love programmingn”);
printf(“You will love it too once ”);
printf(“you know the trickn”);
return 0;
}
statement
statement
statement
statement

Statement
• Statement has two parts :
• Declaration
• The part of the program that tells the compiler the names of memory
cells in a program
• Executable statements
• Program lines that are converted to machine language instructions and
executed by the computer

An Example
/*
Converts distance in miles
to kilometres.
*/
#include <stdio.h> //printf, scanf definitions
#define KMS_PER_MILE 1.609 //conversion constant
int main(void) {
float miles, // input – distance in miles
kms; // output – distance in kilometres
//Get the distance in miles
printf("Enter distance in miles: ");
scanf("%f", &miles);
//Convert the distance to kilometres
kms = KMS_PER_MILE * miles;
//Display the distance in kilometres
printf("That equals %f km.n", kms);
return 0;
}

/*
to kilometres.
*/
int main(void) {
return 0;
}
preprocessor
directives
standard header file
comments
constant
reserved
words
variables
functions
special
symbols
punctuations
An Example

An Example
/*
to kilometres.
*/
int main(void) {
return 0;
}
declarations
Executable
statements

An Example
/*
to kilometres.
*/
int main(void) {
return 0;
}
Sample Run
Enter distance in miles: 10.5
That equals 16.89 km.

At the beginning
memory
MileToKm.exe
miles
?
?
kms
After user enters:
10.5 to
memory
MileToKm.exe
miles
10.5
?
kms
After this line is
executed:
memory
MileToKm.exe
miles
10.5
16.89
kms
 What happens in the computer memory?
Do not assume that
uninitialised variables
contain zero! (Very
common mistake.)
An Example

Variables
• Variable  a name associated with a memory cell whose value can
change
• Variable Declaration: specifies the type of a variable
• Example: int num;
• Variable Definition: assigning a value to the declared variable
• Example: num = 5;

Basic Data Types
• There are 4 basic data types :
• int
• float
• double
• char
• int
• used to declare numeric program variables of integer type
• whole numbers, positive and negative
• keyword: int
int number;
number = 12;

Basic Data Types
• float
• fractional parts, positive and negative
• keyword: float
float height;
height = 1.72;
• double
• used to declare floating point variable of higher precision or higher range
of numbers
• exponential numbers, positive and negative
• keyword: double
double valuebig;
• valuebig = 12E-3; (is equal to 12X10-3)

Basic Data Types
• char
• equivalent to ‘letters’ in English language
• Example of characters:
• Numeric digits: 0 - 9
• Lowercase/uppercase letters: a - z and A - Z
• Space (blank)
• Special characters: , . ; ? “ / ( ) [ ] { } * & % ^ < >
etc
• single character
• keyword: char
char my_letter;
my_letter = 'U';
• In addition, there are void, short, long, etc.
The declared character must be
enclosed within a single quote!

A closer look at variables
19
Memory

int a = 139, b = -5;
20
Memory

int a = 139, b = -5;
21
Memory
a
b
139
-5

int a = 139, b = -5;
22
Memory
a
b
139
-5
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 0 1 1 32 bits

int a = 139, b = -5;
23
Memory
a
b
139
-5
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 1 1 32 bits

char c = ‘H’;
0 1 0 0 1 0 0 0 8 bits

char c = ‘H’;
0 1 0 0 1 0 0 0 8 bits
?

char c = ‘H’;
10010002 = 7210
0 1 0 0 1 0 0 0 8 bits
?

Input/Output Operations
• Input operation
• an instruction that copies data from an input device into
memory
• Output operation
• an instruction that displays information stored in memory to
the output devices (such as the monitor screen)

Input/Output Functions
• A C function that performs an input or output operation
• A few functions that are pre-defined in the header file
stdio.h such as :
• printf()
• scanf()
• getchar() & putchar()

The printf function
• Used to send data to the standard output (usually the monitor) to
be printed according to specific format.
• General format:
• printf(“string literal”);
• A sequence of any number of characters surrounded by
double quotation marks.
• printf(“format string”, variables);
• Format string is a combination of text, conversion specifier
and escape sequence.

The printf function
• Example:
• printf(“Thank you”);
• printf (“Total sum is: %dn”, sum);
• %d is a placeholder (conversion specifier)
• marks the display position for a type
integer variable
• n is an escape sequence
• moves the cursor to the new line

No Conversion
Specifier
Output Type Output Example
1 %d Signed decimal integer 76
2 %i Signed decimal integer 76
3 %o Unsigned octal integer 134
4 %u Unsigned decimal integer 76
5 %x Unsigned hexadecimal (small letter) 9c
6 %X Unsigned hexadecimal (capital letter) 9C
7 %f Integer including decimal point 76.0000
8 %e Signed floating point (using e
notation)
7.6000e+01
9 %E Signed floating point (using E
notation)
7.6000E+01
10 %g The shorter between %f and %e 76
11 %G The shorter between %f and %E 76
12 %c Character ‘7’
13 %s String ‘76'
Placeholder / Conversion Specifier

Escape Sequence
Escape Sequence Effect
a Beep sound
b Backspace
f Formfeed (for printing)
n New line
r Carriage return
t Tab
v Vertical tab
Backslash
” “ sign
o Octal decimal
x Hexadecimal
O NULL

Formatting output
int meters = 21, feet = 68 , inches =
11;
printf("Results: %3d meters = %4d ft.
%2d in.n", meters, feet, inches);
printf("Results: %03d meters = %04d ft.
%02d in.n", meters, feet, inches);
R e s u l t s : 2 1 m e t e r s = 6 8 f t . 1 1 i n .
R e s u l t s : 0 2 1 m e t e r s = 0 0 6 8 f t . 1 1 i n .

Formatting output
• Displaying x Using Format String Placeholder %6.2f

The scanf function
• Read data from the standard input device (usually keyboard) and
store it in a variable.
• General format:
• scanf(“Format string”, &variable);
• Notice ampersand (&) operator :
• C address of operator
• it passes the address of the variable instead of the variable itself
• tells the scanf() where to find the variable to store the new
value

The scanf function
• Example :
int age;
printf(“Enter your age: “);
scanf(“%d”, &age);
• Common Conversion Identifier used in printf and scanf
functions.
printf scanf
int %d %d
float %f %f
double %lf %lf
char %c %c
string %s %s

The scanf function
• If you want the user to enter more than one value, you
serialize the inputs.
• Example:
float height, weight;
printf(“Please enter your height and weight:”);
scanf(“%f%f”, &height, &weight);

Cse115 lecture04introtoc programming

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