C Language Lecture 2

Computing Fundamentals
Dr. Muhammad Yousaf Hamza

C is highly case sensitive
#include <stdio.h>
int main( )
{
int x, y, z, Z;
x = 5;
y = 7;
z = x + y;
Z = x - y;
printf(“%dn", z); // 12
printf(“%d", Z); // -2
getchar();
return 0;
}
//Note: Z is different from z.

Escape Sequences
Sequence Meaning
a Bell (alert)
b Backspace
n Newline
t Horizontal tab
Backslash
' Single quote
" Double quotation

• The name reflects the fact that the backslash
causes an “escape” from the normal way
characters are interpreted.
• In this case, the n is interpreted not as the
character ‘n’ but as the new line character.
Escape Sequences

#include <stdio.h>
int main( )
{
int x, y, z, m;
x = 5;
y = 7;
z = x + y;
m = x - y;
printf("Sum is %dnDifference is %d", z, m);
getchar();
return 0;
}
Sum is 12
Difference is -2
Exercise
Try out various escape
sequences in this program.

#include <stdio.h>
int main( )
{
int x = 5, y = 7, z; // initialization with declaration
z = x + y;
printf(“%d", z);
getchar();
return 0;
}

“Hello World”
//Most of the people write this program first
#include <stdio.h>
int main ( )
{
printf ("Hello World");
getchar();
return 0;
}

More About printf()

More about printf()
• The printf function is used to output information
(both data from variables and text) to standard
output.
• It takes a format string and parameters for output.
a = 10;
b = 20;
• printf("The number is %d", a);
The number is 10
• printf("The numbers are %d and %d",a,b);
The numbers are 10 and 20
• printf("The numbers are %d and %d",a,b*3);
• printf("The numbers are %d and %d",a,b);

More about printf()
The format string contains:
– Literal text: is printed as is without variation
– Escaped sequences: special characters preceeded
by
– Conversion specifiers: % followed by a single
character
• Indicates (usually) that a variable is to be
printed at this location in the output stream.
• The variables to be printed must appear in the
parameters to printf following the format
string, in the order that they appear in the
format string.

C doesn’t care about spaces
#include <stdio.h>
int main ( )
{
printf ("Hello World”);
return 0;
}
#include <stdio.h>
int
main
(
)
{
printf
(
"Hello
World"
)
;
return
0
;
}
Both of these
programs are
the same as far as
your compiler is
concerned.
We SHOULD lay
out our C program
to make them look
nice.

C doesn’t care about spaces
In the most general sense, a statement is a part of
your program that can be executed.
a = 10;
An expression is a statement.
a = a+1;
A function call is also a statement.
printf("%d”, a);
Other statements ……
C is a free form language, so you may type the
statements in any style you feel comfortable:
a=
a+
1;
a = a + 1; a = 6;

#include <stdio.h>
int main( )
{
int x;
x = 5;
printf(“%d", x); // 5
x = x + 3;
printf(“%d", x); // 8
printf(“%d", x*6); // 48
printf(“%d", x); // 6
getchar();
return 0;
}

Punctuation
Punctuations as semicolons, colons, commas,
apostrophes, quotation marks, braces,
brackets, and parentheses will also be used in
C code.
; : , ‘ “ [ ] { } ( )

C Statements
Some Suggestions
• DO: Use block braces on their own line. It is easy
to
find the beginning and end of a block.
– This makes the code easier to read.
{
printf ("Hello, ");
printf ("world");
}
• AVOID: spreading a single statement across
multiple lines if there is no need.
– Try to keep it on one line.

Names of C Variables

• A good name for your variables is important
• Variables in C can be given any name made from numbers,
letters and underscores which is not a keyword and does
not begin with a number.
• Names may contain letters, digits and underscores
• The first character must be a letter or an underscore.
• First 31 characters are significant
(too long name is as bad as too short).
• Are case sensitive:
– abc is different from ABC
• Must begin with a letter or underscore and the rest can be
letters, digits, and underscores.

present, hello, y2x3, r2d3, ... /* OK */
_1993_tar_return /* OK but not good */
Hello#there /* illegal */
int /* shouldn’t work */
2fartogo /* illegal */

int a;
int d;
/* It is like
cryptic */
int start_time;
int no_students;
/* It is better */

Suggestions regarding variable names
• DO: use variable names that are descriptive
• DO: adopt and stick to a standard naming convention
– sometimes it is useful to do this consistently for the entire
software development site
• AVOID: variable names starting with an underscore
– often used by the operating system and easy to miss
• AVOID: using uppercase only variable names
– generally these are pre-processor macros (later)

• C keywords cannot be used as variable names.
• Sometimes called reserved words.
• Are defined as a part of the C language.
• Can not be used for anything else!
• Examples:
– int
– while
– for

Keywords of C
• Flow control (6) – if, else, return, switch,
case, default
• Loops (5) – for, do, while, break, continue
• Common types (5) – int, float, double, char,
void
• Structures (3) – struct, typedef, union

Comments

Comments
• Can be used to write title of the program, author
details etc.
• To guide a programmer. To write a note for function,
operation, logic etc. in between a program.
• Non-executable statement.

Comments: /* This is a comment */
Use them!
Comments should explain:
• special cases
• the use of functions (parameters, return values, purpose)
• explain WHY your code does things the what it does.
• Can’t be nested.
e.g:- /* Hello /* abc */ Hi */ ERROR.
Comments

Comments
• Ideally, a comment with each variable name
helps people know what they do.
• In Lab work, I like to see well chosen variable
names and comments on variables.

More on Comments
For a single line comments, you may use //
For a single line or multiple lines comments, /* comments */ is
used.
A few examples of comments
/* This program calculates area of a rectangle
This program is developed by Mr. XYZ */
length = 5; // in km
width = 3; // in km

C Language Lecture 2

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