1. EECE.2160 ECE Application Programming
Instructors:
Dr. Michael Geiger
Fall 2018
Lecture 23
Character arrays and strings

2. ECE Application Programming: Lecture 23
Lecture outline
Announcements/reminders
Program 5 due 11/7
Exam 2 in class Monday, 11/5
Will cover lectures (except lecture 16)
Lec. 25: Exam 2 Preview (Fri. 11/2)
Today’s lecture
Program 5 overview
Review: Arrays and functions
Character arrays and strings
6/30/2019
ECE Application Programming: Lecture 23

3. ECE Application Programming: Lecture 23
P5 overview
Integral approximation through trapezoidal method
Program split into three files
zyBooks IDE allows you to view one at a time
prog5_integral.c: main() function only
prog5_functions.h: function prototypes
Do not need to modify unless you’re adding function(s)
prog5_functions.c: function definitions
Complete what’s already there
6/30/2019
ECE Application Programming: Lecture 23

4. P5 overview (continued)
General program structure
Read input values (endpoints, # trapezoids)
Call integrate() from main() to perform integral
Repeat program?
User should answer Y/N (case insensitive)
main() mostly responsible for input/output
1 large loop for most of main() repeats if ‘Y’/’y’
Smaller loops for each input prompt (like P4)
Error conditions
Formatting errors for each numeric input
Low endpoint must be < high endpoint
# trapezoids must be at least 1
6/30/2019
ECE Application Programming: Lecture 23

5. ECE Application Programming: Lecture 23
P5: functions
integrate(min, max, trapezoids)
Performs actual integral approximation
f(x)
Function to be integrated
Always fixed as: sin(x) + x2 / 10
badInput()
Used to clear line if formatting error occurs
If written correctly, can generally handle errors as:
if (formatting error)
badInput();
6/30/2019
ECE Application Programming: Lecture 23

6. ECE Application Programming: Lecture 23
P5: trapezoidal method
Range [a, b] split into n trapezoids
Trapezoid width = ∆𝑥= 𝑏 −𝑎 𝑛
Trapezoid area = 0.5 × 𝑏 × ℎ1+ℎ2
= 0.5 × ∆𝑥 × 𝑦 𝑘−1 + 𝑦 𝑘
= 0.5 × ∆𝑥 × 𝑓(𝑥 𝑘−1 )+𝑓( 𝑥 𝑘 )
6/30/2019
ECE Application Programming: Lecture 23

7. P5: trapezoidal method (continued)
Math here is just simplification of basic area calculation
𝐴𝑟𝑒𝑎=0.5 × ∆𝑥 × 𝑦 0 + 𝑦 × ∆𝑥 × 𝑦 1 + 𝑦 2 +…+0.5 × ∆𝑥 × 𝑦 𝑛−1 + 𝑦 𝑛
=0.5 × ∆𝑥 × 𝑦 0 + 𝑦 1 + 𝑦 1 + 𝑦 2 +…+ 𝑦 𝑛−1 + 𝑦 𝑛
=0.5 × ∆𝑥 × 𝑦 0 +2 𝑦 1 +2 𝑦 2 +…+ 2𝑦 𝑛−1 + 𝑦 𝑛
=𝟎.𝟓× ∆𝒙 × 𝒚 𝟎 +𝟐 𝒌=𝟏 𝒏−𝟏 𝒚 𝒌 + 𝒚 𝒏 ≈ 𝑎 𝑏 𝑓 𝑥 𝑑𝑥
6/30/2019
ECE Application Programming: Lecture 23

8. P5: implementation warning
Go through x values  generate y values (trapezoid heights)
How should you code that process?
For loop can iterate over range, but be careful
Wrong idea: loop over x values, i.e.
for (x = a; x < b; x += deltaX) {…}
What’s the potential problem?
What data type should x, a, b, & deltaX be?
All variables of type double  approximations
Rounding errors will affect # loop iterations
Is there a whole number you can use with loop?
# iterations can (and should) be based on n
Iterations might not exactly = n (could be n – 1, n + 1, ?)
6/30/2019
ECE Application Programming: Lecture 23

9. Review: arrays & pointers
Array name is a pointer
Arrays are always passed by address to functions
Should pass size of array as additional argument
e.g. void f(int arr[], int n);
Size of array does not need to be specified in brackets (and will be ignored by compiler)
Calling functions with array arguments: simply specify name of array
For example, given int x[20]; pass that array to f(): f(x, 20);
Array name is pointer to first element: x  &x[0]
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ECE Application Programming: Lecture 23

10. ECE Application Programming: Lecture 23
Strings in C
Strings in C: null-terminated arrays of characters
“Hello”{‘H’, ‘e’, ‘l’, ‘l’, ‘o’, 0}
Null character = 0 = ‘\0’
Can declare array to hold string
Need space to hold null: char hello[5] would be too small
Can use string constants to directly initialize
char hello[] = “Hello”;
Equivalent to:
char hello[6];
hello[0] = ‘H’;
hello[1] = ‘e’;
hello[2] = ‘l’;
hello[3] = ‘l’;
hello[4] = ‘o’;
hello[5] = OR-- hello[5] = ‘\0’;
6/30/2019
ECE Application Programming: Lecture 23

11. Strings and I/O functions
Can pass string as array or pointer: char *
printf(), scanf() take char * as first argument
Given string char hello[] from previous slide:
Print directly: printf(hello);
Print w/formatting using %s: printf(“%s\n”, hello);
Print individual character: printf(“%c\n”, hello[1]);
Overwrite with new string: scanf(“%s”, hello);
Ampersand is unnecessary  array name is already address
scanf() will read up to first whitespace character
6/30/2019
ECE Application Programming: Lecture 23

12. ECE Application Programming: Lecture 23
Final notes
Next time
More on strings
Reminders:
Program 5 due 11/7
Exam 2 in class Monday, 11/5
Will cover lectures (except lecture 16)
Lec. 25: Exam 2 Preview (Fri. 11/2)
6/30/2019
ECE Application Programming: Lecture 23