The document describes a simple "Hello World" C program that prints three strings to the screen. It contains the main() function which uses printf statements to output the text. Comments provide explanations of key elements like header files, escape characters, and functions.

1. Dale RobertsDale Roberts
Department of Computer and Information Science,
School of Science, IUPUI
A First C Program

2. Dale Roberts
#include <stdio.h> /* I/O header file */
main()
{
printf(“Hello world ”);
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.
header file – contains I/O routines
pre-processor directive
one statement
main must be present in each C program
statement terminator
Indicates a
program
building
block called
function
comment

3. Dale Roberts
 Variable 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 else int struct
case entry long switch char extern register
typedef float return union do go sizeof continue
…

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

5. Dale Roberts
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. Dale Roberts
 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. Dale Roberts
• Character literal (covered later)
•American Standard Code for Information Interchange (ASCII)
•Printable: single space 32
‘0’ - ‘9’ 48 - 57
‘A’ - ‘Z’ 65 - 90
‘a’ - ‘z’ 97 - 122
•Nonprintable and special meaning chars
‘n’ new line 10 ‘t’ tab 9
‘’ back slash 9 ‘’’ single quote 39
‘0’ null 0 ‘b’ back space 8
‘f’ formfeed 12 ’r’ carriage return 13
‘”’ 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’ EOT (^D)
‘033’ or ‘X1B’ <esc>

8. Dale Roberts
 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
Example: “ABCD”
...A B C D ‘0’
Ans: 13+1 = 14 bytes
Question: “I am a string” takes ? Bytes
4 chars but takes 5 byte spaces in memory

9. Dale Roberts
• Character literals & ASCII codes:
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)
–if the code used is not ASCII code, one should check out each
value of character
1 38
‘a’ + ‘b’ + ‘c’ = 97 + 98 + 99 = 294 = 256 + 38
in the memory

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

12. Dale Roberts
 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; /* two items */
problem Output
float sum; /* sum of x and y */
float difference; /* difference of x and y */
float product; /* product of x and y */
float quotient; /* quotient of x divided by
y */

13. Dale Roberts
 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. Dale Roberts
#include <stdio.h>
int main(void)
{
float x,y;
float sum;
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);
}
function
• name
• list of argument along with their types
• return value and its type
• Body
inequality operator