1. CSCI206 - Computer Organization & Programming
C grammar, variables, and basic IO
zyBook: 2.3, 2.6, 2.8, 2.11, 2.16

2. A quick, simple, complete C program
Include file,
similar to Python’s
import
#include <stdio.h>
int main(int argc, char * argv[]) {
printf(“Hello world!\n”);
return 0; }
Function parameters,
Similar to Python’s
C function name, similar
to Python’s def name
C statements

3. Coding conventions Names “names should fit” how it is used
Based on Linux kernel coding style
Names
“names should fit” how it is used
lowercase with _ separating words, or camel case
this is the same as in Python and in Java, though most C porgrammers prefer lowercase with _
length proportional to importance
temporary vars can be i, j, k
important vars: student_grade, course_name
include units if appropriate: timeout_msec, height_ft
constants: ALL_CAPS

4. Coding conventions
Indentation and spacing: While indentation in Python is a critical piece of syntax, indentation and spacing in C is more for easier reading and reducing possibilities of errors.
The following two pieces of code do the same.
int func(int a) {
if (a == 0)
return 4;
else
return a * 3 + 4; }
int func(int a) {if (a==0) return 4; else return a*3+4;}

5. C basic types and their ranges
int
INT_MIN and INT_MAX
insigned int
0 and UINT_MAX
float
- FLT_MIN to + FLT_MAX
double
- DBL_MIN to + DBL_MAX
char
Depending on the coding scheme

6. Implicit type conversion
If any value in a numeric expression is floating point, both operands are converted to floating point.
else, integer operations are used.
even if the result would be floating point.
e.g., int x = 4 / 5; // what is x?
e.g., What does it result in Python?
x = 4 / 5 #?
x = 4 // 5 #?

7. Explicit type conversion
Use (type) to force a type conversion.
x = (int) 3.5; // results in x == 3
Note, float->int truncates (doesn’t round).
(int)3.9999; //?
What if we want to round up?

8. String There is no native string data type in C
There is a character data type (char)
A string is a null-terminated sequence of chars
char test[] = “test”;
“test” occupies 5 bytes in memory (include the null terminator!)
Note: unlike Python, strings in C are mutable! t e s \0

9. Manipulating Strings Looping through arrays of char is tedious work...
#include <string.h>
Gives access to a number of useful functions (length, concatenate, copy, etc)
Go read the manual
man 3 string

10. #include <stdio.h>
man 3 printf
printf introduction
"Printf" by I, Surachit. Licensed under CC BY-SA 3.0 via Wikimedia Commons -
printf uses a format string the % character is a special character whose value will be provided by a variable in the variable list.

11. %[flags][width][.precision]type
d,i = integer
u = unsigned integer
f,F,e,E = double
x = hexadecimal unsigned int
s = null terminated string
c = character
p = pointer
% = print the % character

12. Result of executing cbasics

13. %[flags][width][.precision]type
+ = always include +/- for a numeric value
- = left align output (default is right aligned)
0 = use 0 instead of space to pad to a given width

14. %[flags][width][.precision]type
a number
the minimum number of characters to output
defaults to padding on the right with spaces

15. %[flags][width][.precision]type
a number
for floats
the number of digits to the right of the decimal
for strings
the maximum number of characters to output (truncate)

16. printf - example formats
printf( “%5.2f”, ); // _3.14
5-position output (including the decimal), 2 to the right of the decimal, padded on the left with spaces
printf( “%05.2f”, ); // 03.14
same as above but padded on the left with 0’s
printf( “%-5.2f”, ); // 3.14_
same as first, but padded on the right with spaces (cannot right pad with 0’s!)

17. Result of executing cbasics-pos

18. scanf - read input using format strings
int i;
scanf (“%d”, i);

19. scanf - read input using format strings
int i;
scanf (“%d”, i);
Parameters are passed by value, this can’t work!

20. scanf - read input using format strings
int i;
i = scanf (“%d”);

21. scanf - read input using format strings
int i;
i = scanf (“%d”);
There is a return code, it is the number of inputs read (zero means failure)

22. scanf - read input using format strings
int i;
scanf (“%d”, &i);
& is the address-of operator.
This gives the address of the local variable i to scanf
scanf reads an integer (%d) and stores it in the given memory address

23. Loops

24. Decisions

25. Avoid common bugs by ensuring each clause is in parens!
Decisions
Avoid common bugs by ensuring each clause is in parens!
( ) ( )

26. Decisions
warning: case blocks do not start a new scope block and fall through unless you use the break keyword

27. Conversion How many MiB is 2048 KiB? 1.0 2.0 2.048 1024 2048 Go to
socrative.com
Log in as student
Pick “MENG7820” as the classroom
How many MiB is 2048 KiB?
1.0
2.0
2.048
1024
2048

28. Conversion What is 5 KiB in KB? 1.024 4.8828125 5.0 5.120 5.256 Go to
socrative.com
Log in as student
Pick “MENG7820” as the classroom
What is 5 KiB in KB?
1.024
5.0
5.120
5.256