1. The if Statement Format or No Condition satisfied? Yes
if ( condition )
program statement; or {
program statements; }
Condition satisfied? No
Program statement
Yes

2. The if-else Statement Format No Condition satisfied? Yes
if ( condition )
program statement 1;
else
program statement 2;
Condition satisfied? No
Program statement 1
Yes
Program statement 2

3. The else if Statement Format Condition 1 satisfied? No
if ( condition1 )
program statement 1;
else if (condition2)
program statement 2;
Condition 1 satisfied? No
Condition 2 satisfied?
Program statement 1
Yes No
Program statement 2
Yes

4. Boolean Variables Declaration Value _Bool 0 representing false
1 representing true, mostly
Can use any nonzero value representing true in C programming language!

5. Logical Operators Operator Example Description ||
Why
Make a decision based on multiple conditions
What are they
Operator
Example
Description ||
x < 0 || x > width
logical OR
&&
x >= 0 && x <= width
logical AND !
!(x < 0)
Logical NOT

6. Logical OR 1 Returns false only if both expressions are false Example:
(4 > 5 || 6 <= 10)
(4 <= 5 || 6 == 10)
(4 >= 5 || 6 > 10)
(4 < 5 || 6 != 10) A B
A || B
True
False 1

7. A More Complicated Example5:
10:
15:
20:
25:
30:
35:
40:
45:
true
false
#include <stdio.h>
int main() {
int i;
for (i=5; i<50; i+=5)
if((i < 15) || (i >= 35))
printf("%i: true\n", i);
else
printf(“%i: false\n”, i);
}//for
return 0;
}//main

8. Logical AND 1 Returns true only if both expressions are true Examples:
(4 > 5 && 6 <= 10)
(4 <= 5 && 6 == 10)
(4 >= 5 && 6 > 10)
(4 < 5 && 6 != 10) A B
A && B
True
False 1

9. A More Complicated Example5:
10:
15:
20:
25:
30:
35:
40:
45:
false
true
#include <stdio.h>
int main() {
int i;
for (i=5; i<50; i+=5)
if((i > 15) && (i <= 35))
printf("%i: true\n", i);
else
printf(“%i: false\n”, i);
}//for
return 0;
}//main

10. Logical NOT Inverts the Boolean value of an expression A !A True False
Example:
_Bool a = 0;
if (!a) {
printf(“a is a false value (0)\n”); }
a = 1;
if (a) {
printf(“a is a true value (1)\n”); A !A
True
False

11. Conditions Relational expression with ==, !=, >, >=, <, <=
The value of “relational expression” is 1 if the relation is true, and 0 if false. 
Can be combined with the operators (with decreasing precedence)
! (NOT)
&& (AND)
|| (OR)
Rules:
&& and || are evaluated left to right
Short circuiting – a little advanced
Example
c==' ' || c=='\t' || c=='\n'
x < 75 && x > 101 && x != 101
x >= 35 && x < 7 || x == (x >= 35 && x < 7) || x == 10
(F && F) || T ≠ F && (F || T)

12. Evaluate simple expression
Objective:
Evaluate expression and display results with input form
Number operator number
Example
User input:
Program output: 15

13. Program Need to check v2 == 0? #include <stdio.h> int main(void){
float v1, v2;
char operator;
printf("Type in your expression. \n");
scanf("%f %c %f", &v1, &operator, &v2);
if ( operator == '+' )
printf("%.2f\n", v1 + v2);
else if ( operator == '-' )
printf("%.2f\n", v1 - v2);
else if ( operator == '*' )
printf("%.2f\n", v1 * v2);
else if ( operator == '/' )
printf("%.2f\n", v1 / v2);
return 0; }
Need to check v2 == 0?

14. Corrections Change else if ( operator == '/' ) to
printf("%.2f\n", v1 / v2); to {
if ( v2 == 0 )
printf(“Division by zero.\n”);
else }

15. The switch Statement evaluate expression == value 1 statement 1 Y N
When to use
The value of a variable successively compared against different values
Format
switch( expression ) {
case value 1:
program statement 1;
break;
case value 2:
program statement 2; ׃
case value n:
program statement n;
default :
program statement n+1; }
== value 1
statement 1 Y N
== value 2 Y
statement 2 N
== value n Y
statement n N
statement n+1

16. Example switch ( operator ) { case '+': printf("%.2f\n", v1 + v2);
break;
case '-':
printf("%.2f\n", v1 - v2);
case '*':
printf("%.2f\n", v1 * v2);
case '/':
if ( v2 == 0 )
printf(“Division by zero.\n”);
else
printf("%.2f\n", v1 / v2);
default:
printf("Unknown operator!\n"); }

17. Another example Month = 11 November switch (month) {
case 1: printf("January"); break;
case 2: printf("February"); break;
case 3: printf("March"); break;
case 4: printf("April"); break;
case 5: printf("May"); break;
case 6: printf("June"); break;
case 7: printf("July"); break;
case 8: printf("August"); break;
case 9: printf("September"); break;
case 10: printf("October"); break;
case 11: printf("November"); break;
case 12: printf("December"); break;
default: printf("Invalid month."); break; }
Month = 7
July
Month = 14
Invalid month

18. More on switch Statement
case value 1:
program statement 1;
case value 2:
program statement 2;
break;
== value 1
statement 1 Y N
== value 2 Y
statement 2 N

19. One last example switch (month) { case 1: printf("January\n");
case 2: printf("February\n");
case 3: printf("March\n");
case 4: printf("April\n");
case 5: printf("May\n");
case 6: printf("June\n");
default: printf("Invalid month.\n"); }
Month = 11
Ivalid month
Month = 4
April
May
June
Invalid Month

20. The conditional operator
Format:
condition ? expression1 : expression2;
Same as
if ( condition ) {
expression1; }
else {
expression2;

21. Conditional example //find the absolute value of a
abs = a < 0 ? -a : a;