Fundamentals of C

CSE 4373: Computer Programming and Applications

Ajwad Abrar
Junior Lecturer, CSE
Writing a simple program
#include<stdio.h>

int main()

printf(“To C or not to C, that is the question.”);

return 0;

What really happens when you run this program?

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Printing strings

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Printing strings
printf(“To C or not to C, that is the question.”);
● Will print anything enclosed between double quotation marks (“ ”)
● Things to be careful about:
○ Don’t forget the closing brackets
○ Don’t forget the semicolon (;)

Yes it’s that simple !

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Pop Quiz

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Printing strings

What is the output for the given line?

printf(“Why did the turkey cross the road?”);

printf(“To prove it wasn’t a chicken!”);

Will it be printed on a new line?

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Escape sequences
Sometimes, it is necessary to use characters that cannot be typed or has some special
meaning in C programming. To use those, escape sequences are used.

\n New line \’ Single

quotation

\t Horizontal \” Double
tab quotation

\v Vertical \0 Null
tab

\\ Backslash \b backspace

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Comments

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Comments
Multiline Comments (C89 Style)

/* int main()
{
This is an example of a printf(“Hello!”); /*Comment*/
}
multiline comment.

*/

printf(“Very insightful comments”);

● Used for documenting code

● Starts with /* and ends with */

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Comments
Single line Comments (C99 Style)

//This is a comment int main()

{
//It only spans a single line printf(“Hello!”); //comment
}
printf(“Very insightful comments”);

● Begins with //
● Ends when the line ends
● No need for a closing symbol

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Comments
Write comments that are helpful. Do not write comments that state the obvious

● Follow a convention and stick to it

● Be expressive
● Increases
○ clarity,
○ readability and
○ maintainability of the code

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Variables

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Just a fancy name for
containers

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Variables

Numbers Words Images Anything

Each container must have a unique name

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Variables in C
● Each variable must have a type and an identifier
● Data type specifies what kind of data will be stored

There are a lot of data types in C:

int, float, char, double, short int, unsigned int, long int

And many more. But for now, we are concerned with: int, float

int float

● Holds integers ● Holds floating point numbers

● Limited range (-32,768 to +32767) ● Larger range
● Might cause round-off error

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Declaring variables
All variables must be declared before usage

datatype identifier;
Examples:

int count;

float salary;

Several same type variable declarations can be combined:

int count, steps, length, width;

float salary, volume, profit, loss;

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Assigning variables
Variables can be given a value to store through assignment

int count; int count = 10, steps = count;

int count = 10;
float salary; float salary = 12.4f, volume = 0.93f;
float salary = 12.4f;
count = 10;

salary = 12.4f;

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Best practices

It’s best practice to append Whenever assigning values to

the letter f to a floating-point float without any digits after
assignment: the decimal point, make sure to
float salary = 12.4f; add a zero after the decimal.

float sum, angle;

sum = 0.0;

angle = 45.0;

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Pop Quiz

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Printing strings
What is stored in the variable?
height = 8;
int height;

What about this?

int length, width = 10;

Is this even possible?

int length = 12.4; float profit = 2150;
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Assigning variables

● Some variables are automatically set to zero when a

program begins to execute, but most are not
● A variable is said to be uninitialized
○ Doesn’t have a default value, or
○ Hasn’t yet been assigned a value by the program
● Attempting to access uninitialized variable can yield
unpredictable result, even a program crash

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Printing variables

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Printing variables

● Use printf function to display the current value of a variable

int total = 100;

printf(“%d”, total);

%d is placeholder indicating where the value of total should be

printed. It is called a format specifier.
● %d is for int %f is for float

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Printing variables

● By default, %f prints six digits after the decimal point

● To force %f to print p digits after the decimal point, we put .p
between % and f
● There’s no limit to the number of variables that can be printed
by a single printf

float volume = 131.45123;

printf(“%.3f”, volume)
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Taking input

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Taking input

● scanf is the C library’s counterpart to printf

● Similar to printf, scanf requires a format string to
specify the type of the input
To read an integer from the user:
scanf("%d", &i); // reads an integer; stores it in i

Reading a float value requires:

scanf("%f", &j); // reads a float; stores it in j

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Identifiers

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Rules of Identifier Specification
Identifiers are just the names of the variables
● May contain letters, digits, and underscores
● Must begin with a letter or underscore
● C identifiers are Case Sensitive. Age, age, AGE, agE are
all different identifiers
● C places no limit on the maximum length of an identifier

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Pop Quiz

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Rules of Identifier Specification
Are these identifiers legal?

times10, _done, TotalProfit$, HOUSE NUMBER,

1st_Slot, __memberValue, last<>Quest, int

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Keywords
● Keywords are words that have special meaning to the C compiler
● They can’t be used as identifiers
● Some keywords are

auto, enum, restrict, unsigned, break, extern, return,

void, case, float, short, volatile, char, for, signed,
while, do, int, switch, double, long, typedef, else,
register, union

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Reading Tasks
● C Programming - A Modern Approach | Section 2.1 ~ 2.7
● Teach yourself C | Section 1.1, 1.3 ~ 1.4

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Thank You

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