If statements and relational operators allow programmers to control program flow based on conditions. There are three types of if statements: if, if-else, and if-else-if. Relational operators like ==, <, > are used to form conditions. The if statement executes code if the condition is true, while if-else executes one block if true and another if false. Boolean logic and data type bool can be used to build more complex conditional expressions. Examples demonstrate using if statements and relational operators to check values, qualify ages to vote, and determine positive/negative numbers.

1. PROGRAMMING
IF STATEMENTS &
RELATIONAL
OPERATORS
By: John Paul Espino
De La Salle University – Dasmarinas
Facebook.com/Johnpaul.dss

3. CONDITIONAL STATEMENTS
• A conditional statement allows us to control whether a program segment is executed or not.
• Two constructs
• if statement
• if
• if-else
• if-else-if
• switch statement

4. THE BASIC IF STATEMENT
• Syntax
if(condition)
action
• if the condition is true then
execute the action.
• action is either a single
statement or a group of
statements within braces.
condition
action
true
false

5. CHOICE (IF)
 Put multiple action statements
within braces
if (it's raining){
printf(“take umbrella”);
printf(“wear raincoat”);
}

6. ABSOLUTE VALUE
// program to read number & print its absolute value
#include <stdio.h>
main(){
int value;
printf("Enter integer: “);
scanf(“%d”,&value);
if(value < 0)
value = -value;
printf("The absolute value is %d “,value);
getch();
}

7. RELATIONAL OPERATORS
Relational operators are used to compare two values to form a
condition.
Math C Plain English
= == equals [example: if(a==b) ]
[ (a=b) means put the value of b into a ]
< < less than
 <= less than or equal to
> > greater than
 >= greater than or equal to
 != not equal to

8. CONDITIONS
Examples:
Number_of_Students < 200
10 > 20
20 * j == 10 + i

9. THE BOOLEAN TYPE
• C contains a type named bool for conditions.
• A condition can have one of two values:
• true (corresponds to a non-zero value)
• false (corresponds to zero value)
• Boolean operators can be used to form more complex conditional
expressions.
• The and operator is &&
• The or operator is ||
• The not operator is !

10. THE BOOLEAN TYPE
• Truth table for "&&" (AND):
Operand1 Operand2 Operand1 &&
Operand2
true true true
true false false
false true false
false false false

11. THE BOOLEAN TYPE
• Truth table for “||" (OR):
Operand1 Operand2 Operand1 ||
Operand2
true true true
true false true
false true true
false false false

12. THE BOOLEAN TYPE
• Truth table for "!" (NOT):
Operand !Operand
true false
false true

13. A BOOLEAN TYPE
• Assignments to bool type variables
bool P = true;
bool Q = false;
bool R = true;
bool S = P && Q;
bool T = !Q || R;
bool U = !(R && !Q);

14. “IF” WITH A BLOCK OF STATEMENTS
if (aValue <= 10)
{
printf("Answer is %.2fn", aValue);
countB++;
}

15. POSITIVE OR NEGATIVE
#include <stdio.h>
main()
{
int number;
clrscr();
printf(“Enter a number”);
scanf(“%d”,&number);
if (number>0)
printf(“It is Positive”);
getch();
}

16. IF-ELSE STATEMENT

17. SYNTAX OF IF-ELSE STATEMENT
if ( condition)
statement;
else
statement;

18. IF – ELSE WITH A BLOCK OF STATEMENTS
if (aValue <= 10)
{
printf("Answer is %.2fn", aValue);
countB++;
} End if
else
{
printf("Error occurredn");
countC++;
} End else

19. TO VOTE OR NOT TO VOTE
#include<stdio.h>
main()
{
int age;
clrscr();
printf(“Enter your age”);
scanf(“%d”,&age);
if (age>=18)
printf(“You are qualified to vote”);
else
printf(“Not qualified to vote”);
getch();
}

20. POSITIVE OR NEGATIVE
#include <stdio.h>
main()
{
int number;
clrscr();
printf(“Enter a number”);
scanf(“%d”,&number);
if (number>0)
printf(“Positive number”);
else
printf(“Negative number”);
getch();
}