1. EECE.2160 ECE Application Programming
Instructors:
Dr. Michael Geiger & Dr. Lin Li
Spring 2019
Lecture 8:
If statements
Program 3 overview

2. Announcements/reminders
Textbook exercises due 3 days after each lecture
Program 2 due today
Program 3 due Monday, 2/25
zyBooks IDE now allows interactive program runs—will demonstrate later in class
Exam 1: Friday, 2/22
Allowed one double-sided 8.5” x 11” note sheet
No other notes, no electronic devices
Old exams at link on course home page (
4/27/2019
ECE Application Programming: Lecture 8

3. ECE Application Programming: Lecture 8
Today’s lecture
Review
If statements
Else blocks
Else if blocks
Program 3 overview
4/27/2019
ECE Application Programming: Lecture 8

4. ECE Application Programming: Lecture 8
Review: Decisions
Conditionally execute some path
May want to:
Only perform operation if condition is true:
A = 0?
TRUE
FALSE
A = 0?
TRUE
X = x + 1
FALSE
4/27/2019
ECE Application Programming: Lecture 8

5. ECE Application Programming: Lecture 8
Review: if statements
Conditional execution using if statements:
Form:
if (<expression>)
<statement>
Expression frequently uses relational operators to test equality/inequality
< > <= >= == !=
e.g., if (x <= 5)
Can combine conditions using logical operators
AND : && OR: ||
e.g., if (x <= 5 && x > 0)
Can test if condition is false using logical NOT: !
e.g., if (!(x < 5))
4/27/2019
ECE Application Programming: Lecture 8

6. ECE Application Programming: Lecture 8
Decisions (cont.)
May want to:
Perform one operation if condition is true, another if false:
Uses if/else construct
A = 0?
TRUE
x = x + 1
FALSE
x = x - 1
4/27/2019
ECE Application Programming: Lecture 8

7. ECE Application Programming: Lecture 8
If/else
if (A == 0) x = x + 1; else x = x - 1;
if (a+6*3-43) printf("wow is this not cool"); else printf("this is not cool");
4/27/2019
ECE Application Programming: Lecture 8

8. ECE Application Programming: Lecture 8
Decisions (cont.)
May want to:
Check multiple conditions, in order
A = 0?
TRUE
x = x + 1
FALSE
B=1?
TRUE
x = x - 1
FALSE
x = 0
4/27/2019
ECE Application Programming: Lecture 8

9. ECE Application Programming: Lecture 8
If/else if
if (A == 0)
x = x + 1;
else if (B == 1)
x = x – 1;
else
x = 0;
No limit on number of else if blocks
else block isn’t required, even if you use else if
4/27/2019
ECE Application Programming: Lecture 8

10. ECE Application Programming: Lecture 8
if (common pitfalls)
a single equals means ASSIGN.
a double equal must be used to check for equality.
x=12345;
if (x=3) { printf("x is 3\n"); } else { printf("x is not 3\n"); }
This code will ALWAYS print: x is 3
4/27/2019
ECE Application Programming: Lecture 8

11. ECE Application Programming: Lecture 8
if (example)
void main(void) { float a,b,c,disc; : scanf("%f %f %f",&a,&b,&c); if (a==0) { // statements } else { disc = b*b-4*a*c; if ( disc < 0 ) { // statements } else { // statements } } }
4/27/2019
ECE Application Programming: Lecture 8

12. Example: if statements
What does the following code print?
int main() {
int x = 3;
int y = 7;
if (x > 2)
x = x - 2;
else
x = x + 2;
if ((y % 2) == 1) {
y = -x;
if ((x != 0) && (y != -1))
y = 0; }
printf("x = %d, y = %d\n", x, y);
return 0;
4/27/2019
ECE Application Programming: Lecture 8

13. ECE Application Programming: Lecture 8
Example solution
int main() {
int x = 3;
int y = 7;
if (x > 2)  Condition is true, since 3 > 2
x = x - 2;  x set to 1
else
x = x + 2;
if ((y % 2) == 1)  Tests if y is an odd number--true condition {
y = -x;  y set to -1
if ((x != 0) && (y != -1))  First part of condition is true,
second part is false--overall false
y = 0; }
printf("x = %d, y = %d\n", x, y);  Prints: x = 1, y = -1
return 0;
4/27/2019
ECE Application Programming: Lecture 8

14. Program 3: bitwise operators
Basic 1-bit Boolean calculator
1-bit values = 0 or 1
Boolean operations: bitwise logical operations
& (AND), | (OR), ^ (XOR)
Not the same as &&, || used to combine conditions
Bitwise operators are binary operators
Given unsigned x = 1; unsigned y = 0;
printf("x | y = %u, x & y = %u, x ^ y = %u\n", x | y, x & y, x ^ y); would print
x | y = 1, x & y = 0, x ^ y = 1
4/27/2019
ECE Application Programming: Lecture 8

15. Bitwise Logical Operations
AND A B
A&B 1
NOT (not needed for P3) A
~ A 1 OR
XOR (exclusive or) A B
A|B 1 A B
A^B 1
4/27/2019
ECE Application Programming: Lecture 8

16. Program 3: conditional statements
Conditional statements will be required to
Check for errors
Evaluate which operator user entered
Don’t use conditional statements to evaluate bitwise operations!
You don’t need to directly implement truth tables
Operators will do that work for you
4/27/2019
ECE Application Programming: Lecture 8

17. ECE Application Programming: Lecture 8
Final notes
Next time
Range checking with if statements
Reminders:
Textbook exercises due 3 days after each lecture
Program 2 due Monday, 2/11
4/27/2019
ECE Application Programming: Lecture 8