The document provides an introduction to the basics of writing a C program. It explains that a C program contains functions, with main() being required. The main() function contains statements that are terminated with semicolons. It also describes common data types in C like int, char, and float, and how to declare variables. The document shows how to use literals, initialize variables, and take user input using scanf.

1. A First C Program

2. Try#include <stdio.h> C/*Program */
Your First
I/O header file
pre-processor directive
header file – contains I/O routines
main()
Indicates a {
program
building
block called
function
comment
main must be present in each C program
one statement
printf(“Hello world ”);
statement terminator
printf(“Welcome to CSCI230n“);
printf(“I am John Smithn”);
}
A C program contains one or more functions
 main() is the function name of your main (root) program
 { }: braces (left & right) to construct a block containing the statements of a
function
 Every statement must end with a ;
 is called an escape character
 n is an example of an escape sequence which indicates newline
 Other escape sequences are: t r a ”
Exercise: Use any editor to type and then save your first program as main.c
% gcc main.c
% a.out
and observe its result.


3. 
Variable identifiers
Identifiers

Begin with a letter or underscore: A-Z, a-z, _

The rest of the name can be letters, underscore, or digits

Guarantee that east least the first 8 characters are significant (those
come after the 8th character will be ignored) while most of C
compiler allows 32 significant characters.
Example:
_abc ABC
Time time
_a1 abcdefgh
abcdefghi (may be the same as abcdefgh)

Case sensitive

Keywords: reserved names (lexical tokens)
auto double if static break
case entry
long
typedef float
else
switch char
return union
int struct
extern register
do go sizeof continue
…

4. 
Fundamental Data Type
Four Data Types (assume 2’s complement, byte machine)
Data Type
Size
(byte)
Range
char
1
-128 ~ 127
unsigned char
char
Abbreviation
1
0 ~ 255
2 or 4
-215 ~ 215-1 or -231 ~ 231-1
2 or 4
0 ~ 65535 or 0 ~ 232-1
int
unsigned int
short int
short
2
-32768 ~ 32767
unsigned short int
unsigned short
2
0 ~ 65535
long int
long
4
-231 ~ 231-1
unsigned long int
int
unsigned
unsigned long
4
0 ~ 232-1
float
double
Note:
4
8
27 = 128, 215 =32768, 231 = 2147483648
Complex and double complex are not available

5. Variable Declarations
type v1,v2,v3, …, vn
Example:
int i;
int j;
float k;
char c;
short int x;
long int y;
unsigned int z;
int a1, a2, a3, a4, a5;

6. 
Numeric, Char, String Literals
Literal

Numeric literal

fixed-point

octal
O32 (= 24D) (covered later)

hexadecimal
OxFE or Oxfe (=254D) (covered later)

decimal int
32

long (explicit)
32L or 32l

an ordinary integer literal that is too long to fit in an int is also too long for long

floating-point

No single precision is used; always use double for literal
Example:
1.23
123.456e-7
0.12E

7. Numeric, Char, String Literals
• Character literal (covered later)
• American Standard Code for Information Interchange (ASCII)
single space
32
‘0’ - ‘9’
48 - 57
‘A’ - ‘Z’
65 - 90
‘a’ - ‘z’
• Printable:
97 - 122
• Nonprintable and special meaning chars
„n‟
new line
„‟ back slash
„0‟ null
9
0
„f‟ formfeed
10
„t‟ tab
„‟‟ single quote 39
„b‟ back space
12
8
‟r‟ carriage return
„”‟ double quote 34
„ddd‟ arbitrary bit pattern using 1-3 octal digits
„Xdd‟ for Hexadecimal mode
„017‟ or „17‟ Shift-Ins, ^O
„04‟ or „4‟ or „004‟
„033‟ or „X1B‟
9
<esc>
EOT (^D)
13

8. Numeric, Char, String Literals

String Literal

will be covered in Array section

String is a array of chars but ended by „0‟

String literal is allocated in a continuous memory space of
Data Segment, so it can not be rewritten
A B C D „0‟ ...
Example:
“ABCD”
4 chars but takes 5 byte spaces in memory
Question: “I am a string” takes ? Bytes
Ans: 13+1 = 14 bytes

9. Numeric,literals & ASCII codes:
• Character Char, String Literals
char x;
x=„a‟;
/* x = 97*/
Notes:
– „a‟ and “a” are different; why?
„a‟ is the literal 97
“a” is an array of character literals, { „a‟, „0‟} or {97, 0}
– “a” + “b” +”c” is invalid but „a‟+‟b‟+‟c‟ = ? (hint: „a‟ = 97 in ASCII)
„a‟ + „b‟ + „c‟ = 97 + 98 + 99 = 294 = 256 + 38
in the memory
1
38
– if the code used is not ASCII code, one should check out each
value of character

10. Initialization

If a variable is not initialized, the value of variable may
be either 0 or garbage depending on the storage class of
the variable.
int i=5;
float x=1.23;
char c=„A‟;
int i=1, j,k=5;
char c1 = „A‟, c2 = 97;
float x=1.23, y=0.1;

11. 
Memory Concepts
Each variable has a name, address, type, and value
1)
int x;
2)
scanf(“%d”, &x);
3)
user inputs
4)
x = 200;
10
After the execution of (1)
After the execution of (2)
x
After the execution of (3)
x
After the execution of (4)
x
x
Previous value of x was overwritten
10
200

12. Sample Problem

Write a program to take two numbers as input
data and print their sum, their difference,
their product and their quotient.
Problem Inputs
float x, y;
/*
problem Output
float sum;
/*
float difference;
x and y */
float product; /*
y */
float quotient; /*
divided by y */
two items */
sum of x and y */
/* difference of
product of x and
quotient of x

13. Sample Problem

(cont.)
Pseudo Code:
Declare variables of x and y;
Prompt user to input the value of x
and y;
Print the sum of x and y;
Print the difference of x and y;
Print the product of x and y;
If y not equal to zero, print the
quotient of x divided by y

14. Example Program
#include <stdio.h>
int main(void)
{
float x,y;
float sum;
function
• name
• list of argument along with their types
• return value and its type
• Body
printf(“Enter the value of x:”);
scanf(“%f”, &x);
printf(“nEnter the value of y:”);
scanf(“%f”, &y);
sum = x + y;
printf(“nthe sum of x and y is:%f”,sum);
printf(“nthe sum of x and y is:%f”,x+y);
printf(“nthe difference of x and y is:%f”,x-y);
printf(“nthe product of x and y is:%f”,x*y);
if (y != 0)
printf(“nthe quotient of x divided by y is:%f”,x/y);
else
printf(“nquotient of x divided by y does not exist!n”);
return(0);
}
inequality operator