C Language Lecture 3

Computing Fundamentals
Dr. Muhammad Yousaf Hamza

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

scanf()

Example
#include <stdio.h>
int main ()
{
int num, result_square;
printf ("Enter an integer value please: ");
scanf ( "%d", &num);
result_square = num*num;
printf ("Square of your entered number is %dn",
result_square);
getchar();
return 0;
}

Reading Numeric Data with scanf
• Reading input from keyboard
• scanf can be used like printf but to read instead of write.
• The scanf function is the input equivalent of printf
– A C library function in the <stdio.h> library
– Takes a format string and parameters, much like printf
– The format string specifiers are nearly the same as those used in
printf
• Examples:
scanf ("%d", &x); /* reads a decimal integer */
• The ampersand (&) is used to get the “address” of the
variable (Later)
– If we use scanf("%d",x) instead, the value of x is passed. As a
result, scanf will not know where to put the number it reads.

• Reading more than one variable at a time:
– For example:
int n1, n2, n3;
scanf("%d%d%d",&n1,&n2,&n3);
– Use white spaces to separate numbers when input.
5 10 22
• In the format string:
– You can use other characters to separate the numbers
int no_students, no_chairs;
scanf(“%d%d", &no_students, &no_chairs);

#include <stdio.h>
int main( void )
{
int value1, value2, sum, product ;
printf(“Enter two integer values: ”) ;
scanf(“%d %d”, &value1, &value2) ;
sum = value1 + value2 ;
product = value1 * value2 ;
printf(“Sum is = %d nnProduct = %dn”, sum, product) ;
getchar();
return 0 ;
}
Example

The scanf statement
int number, check;
scanf ("%d",&number);
check= number;
//Correct
int number, check;
check= scanf ("%d",&number);
/*The program may run without error.
However, on printing the value of check,
it would not be same as number */

#include <stdio.h>
int main(void)
{
int x, y, z;
x = scanf("%d %d", &y, &z);
printf("%d", x);
getchar();
return 0;
}
Ans: 2
// x will tell how many values scanned.

Expressions and Operators

Expressions and Operators
• In the most general sense, a statement is a part of your
program that can be executed.
• An expression is a statement.
• Examples:
x = 4;
x = x + 1;
printf("%d",x);
• The expressions are formed by data and operators
• An expression in C usually has a value
– except for the function call that returns void. (later)

Arithmetic Operators
Operator Symbol Action
Addition + Adds operands x + y
Subtraction - Subtracts from first x - y
Negation - Negates operand -x
Multiplication * Multiplies operands x * y
Division / Divides first by second x / y
(integer quotient)
Modulus % Remainder of divide op x % y
• (x % y) gives the remainder when x is divided by y
• remainder= x%y; (ints only)

The Use of Modulus
• int x;
• // Various cases
• x = 6%2 // x =
• x = 7%2 // x =
• Suppose num is any even number then
• x = num%2 // x =
• Suppose num is any odd number then
• x = num%2 // x =
• // Some other examples
• x = 63%10 // x =
• x = 100 %7 // x =

• int x;
• // Various cases
• x = 6%2 // x = 0
• x = 7%2 // x = 1
• Suppose num is any even number then
• x = num%2 // x = 0
• Suppose num is any odd number then
• x = num%2 // x = 1
• // Some other examples
• x = 63%10 // x = 3
• x = 100 %7 // x = 2
The Use of Modulus

include<stdio.h>
int main()
{
int num=12;
int digit1,digit2;
digit1=num%10; // digit1 = 2
digit2=num/10; // digit2 = 1
printf(“First digit is = %d ”,digit1);
printf(“nSecond digit is =%d”,digit2);
getchar();
return 0;
}
The Use of Modulus

Assignment Operator
• The assignment operator =
x = 3
– It assigns the value of the right hand side (rhs) to
the left hand side (lhs).
– The value is the value of the rhs.
• For example:
x = ( y = 3 ) +1; /* y is assigned 3 */
/* the value of (y=3) is 3 */
/* x is assigned 4 */

Compound Assignment Operator
• Often we use “update” forms of operators
x=x+1, x=x*2, ...
• C offers a short form for this:
Operator Equivalent to:
x + = y x = x + y
x *= y x = x * y
y -= z + 1 y = y - (z + 1)
a /= b a = a / b
x += y / 8 x = x + (y / 8)
y %= 3 y = y % 3

// demonstrates arithmetic assignement operators
#include <stdio.h>
int main()
{
int ans = 27;
ans += 10; //same as: ans = ans + 10;
printf(" %d, ",ans);
ans -= 7; //same as: ans = ans - 7;
ans *= 2; //same as: ans = ans * 2;
ans /= 3; //same as: ans = ans / 3;
ans %= 3; //same as: ans = ans % 3;
printf(" %d, n",ans);
getchar(); return 0;
} Dr. Muhammad Yousaf Hamza

Increment and Decrement Operators

Increment and Decrement
• Increment and decrement operators.
– Increment: ++ It increases the value by 1
i = 7; // i is a variable name
++i; // (i = i + 1 or i + = 1). It increases the value of i by 1
i = 7;
i++;
–Decrement: -- (similar to ++) It decreases the value by 1
i = 8;
--i; // --i is the same as : (i = i – 1 or i - = 1).
i = 8;
i--;

• ++i means increment i then use it
• i++ means use i then increment it
int i= 6;
printf ("%dn",i++); /* Prints 6 sets i to 7 */
int i= 6;
printf ("%dn",++i); /* prints 7 and sets i to 7 */
Note this important difference
All of the above also applies to --.
Pre-fix and Post-fix

#include<stdio.h>
int main()
{
int a = 7, b = 20, c, d;
c = a++;
printf("%d", c);
printf("n%d",a);
d = ++b;
printf("n%d", d);
printf("n%d",b);
getchar();
return 0;
}
Pre-fix and Post-fix

Data Types

Data Types in C
• We must declare the type of every variable we
use in C.
• Every variable has a type (e.g. int) and a name
(e.g. no_students), i.e. int no_students
• Basic data types in C
– char: a single byte, capable of holding one
character
– int: an integer of fixed length, typically reflecting
the natural size of integers on the host
machine (i.e., 32 or 64 bits)
– float: single-precision floating point
– double: double precision floating point

• Floating-point variables represent numbers
with a decimal place—like 9.3, 3.1415927,
0.0000625, and –10.2.
• They have both an integer part to the left of
the decimal point, and a fractional part to the
right.
• Floating-point variables represent what
mathematicians call real numbers.
Data Types in C

Conversion Specifiers
#include <stdio.h>
int main( )
{
int x = 5;
printf(“n x is %d", x); // %d is format specifier
getchar();
return 0;
}
Format specifiers are used in printf function for printing
numbers and characters. A format specifier acts like a place
holder, it reserves a place in a string for numbers and
characters.

Conversion Specifiers
Specifier Meaning
%c Single character
%d Decimal integer
%f Decimal floating point number
%lf Decimal floating point number (double)
There must be one conversion specifier for each argument
being printed out.
• Ensure you use the correct specifier for the type of data you are
printing.
• Format specifiers are used in printf function for printing
numbers and characters. A format specifier acts like a place
holder, it reserves a place in a string for numbers and
characters.

Variable Declaration
• Generic Form
typename varname1, varname2, ...;
• Examples:
int count, x, y, z;
float a, b, m;
double percent, total, average;

Variable Declaration
Initialization
• ALWAYS initialize a variable before using it
– Failure to do so in C is asking for trouble
– The value of an uninitialized variables is undefined in
the C standards
• Examples:
int count; /* Set aside storage space for count */
count = 0; /* Store 0 in count */
• This can be done at definition:
int count = 0;
double percent = 10.0, rate = 0.56;

Example
#include <stdio.h>
int main ()
{
double radius, area;
printf ("Enter the value of radius ");
scanf ( "%lf", &radius);
area = 3.14159 * radius * radius;
printf ("nArea = %lfnn", area);
getchar();
return 0;
} Dr. Muhammad Yousaf Hamza

– For example:
int n1, n2,x;
float f, rate;
scanf ("%d",&x); /*reads a decimal integer */
scanf ("%f",&rate); /*reads a floating point value*/
scanf("%d%d%f",&n1,&n2,&f);
• Use white spaces to separate numbers when input.
5 10 20.3 then press Enter Key
OR, you can also enter these values one by one by
pressing enter Key. Both are OK.

Type Conversion
#include<stdio.h>
int main()
{
int a= 23, b= 4;
float c;
c = a/b; // 5.00
printf("n%f",c); // 5.00
getchar();
return 0;
}
Actually 23/4 = 5.75, but here output is 5.00 In order to have
correct answer (with decimal value), we need type casting.

Type Conversion
• C allows for conversions between the basic types, implicitly or
explicitly. It is also called casting.
• A cast is a way of telling one variable type to temporarily look
like another.
• Explicit conversion uses the cast operator.
• Example :
int x=10;
float y, z=3.14;
y=(float) x; /* y=10.0 */
x=(int) z; /* x=3 */
x=(int) (-z); /* x=-3 */

By using (type) in front of a variable we tell
the variable to act like another type of variable.
We can cast between any type usually. However,
the only reason to cast is to stop
ints being rounded by division.
Casting of Variables

#include<stdio.h>
int main()
{
int a= 23, b= 4;
float c;
c = a/b;
printf("n%f",c); // 5.00
c= (float)a/(float)b;
// c = (float)a/b; or c= a/(float)b; are also same.
printf("n%f",c); // 5.75
getchar();
return 0;
}
Casting of Variables
Cast ints a and b to be float

More types: const
const means a variable which doesn't vary – useful for
physical constants or things like pi or e
– You can also declare variables as being constants
– Use the const qualifier:
const double pi=3.1415926;
const long double e = 2.718281828;
const int maxlength=2356;
const int val=(3*7+6)*5;
•(scientific) notation
(mantissa/exponent)
onst double n = 6.18e2;
• 6.18e2 = 6.18x10^2
#include<stdio.h>
int main()
{
const float n = 6.18e2;
printf("%f",n); 618.00
getchar();
return 0;
}

Constants
– Constants are useful for a number of reasons
• Tells the reader of the code that a value does not
change
• Tells the compiler that a value does not change
– The compiler can potentially compile faster code
• Use constants where appropriate
More types: const

#include<stdio.h>
int main()
{
float radius = 4.5,circum ;
circum = 2*pi*radius;
printf("n%f", circum); // 28.274334
getchar();
return 0;
}
More types: const

#include<stdio.h>
int main()
{
float radius = 4.5,circum ;
printf("n%f", circum);
radius = 7.3;
pi = 2.9; // Error
printf("n%f", circum);
getchar();
return 0;
}
More types: const

Decisions

To decide even/odd
#include<stdio.h>
int main()
{
int num;
printf("Please enter an integer number:n");
scanf("%d",&num);
if(num%2==0)
printf("nThe number %d is an even number",num);
if(num%2!=0)
printf("nThe number %d is an odd number",num);
getchar(); getchar();
return 0;
}

To decide even/odd
#include<stdio.h>
int main()
{
int num;
printf("Please enter an integer number:n");
scanf("%d",&num);
if(num%2==0) // Here only one check.
printf("nThe number %d is an even number",num);
else
printf("nThe number %d is an odd number",num);
getchar(); getchar();
return 0;
}

C Language Lecture 3

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