The document discusses the syntax of if control structures in C, including relational operators like <, >, <=, >=, ==, and !=. It provides examples of if statements using these relational operators to evaluate expressions that return 1 if true or 0 if false, and then execute the code block accordingly.

1. Syntax of
if control structure in C

2. Relational Operators in C
Operator
Meaning
Example
Value of the
expression
<
less than
age < 30
>
greater than
height > 6.2
<=
less than or equal to
taxable <= 20000
Value is 0
(Zero) if
expression is
false
>=
greater than or equal to
temperature >= 98.6
==
equal to
marks == 100
!=
not equal to
number != 250
Value is 1 (one)
if expression is
True

3. if(x<y)
{
……….
……….
}
if(‘a’<‘P’)
{
……….
……….
}
If x contains 5 and y contains 10
then value of the expression is
1 and condition is true
If x contains 10 and y contains 4
then value of the expression is
0 and condition is false
As ASCII value of A is 97 and ASCII
value of P is 80 the expression is
false and value of the expression
is 0
If block

4. if(-5)
{
……….
……….
}
Valid condition. -5 is a truth
value and is non zero. So value
of the expression is 1 and
statement is true!
if(x)
{
……….
……….
}
If x contains any non zero value
the expression is true and value of
the expression is 1.
If x contains zero, value of the
expression is 0 and statement is
false