1. B. Ramamurthy University at Buffalo bina@buffalo.edu
The C Language
B. Ramamurthy
University at Buffalo
cse
9/18/2018

2. Introduction
About C language: “.. features economy of expression..”; written for Unix Operating system (1978)
The C Language since then has taken a life of it own and has become the foundation for many modern languages.
It has also become a language of choice for RTOS.
Reference: The C Programming Language by Kernighan & Ritchie (available online)
We will learn C by repeated spiral mode hands-on exposure to various elements of the language
We will also try to work on the Linux system and another system called Nexos (Next generation embedded operating system) at the CSE department.
cse
9/18/2018

3. Program Structure
A C program is a collection of functions with at least one function called “main”
Here is the classical example that has become a metaphor for a first program in any language.
Hello World: lets compile it and see what happens.
#include <stdio.h>
int main () {
printf(“Hello World \n”);
return 0; }
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4. Processing the C program
Save the program in a file called “hello.c”
Compile it using an appropriate compiler
CC or cc or gcc or g++ (where G/g stands for “gnu” organization)
Compiler parses the input, checks for syntax correctness and if syntax is correct generates code;
This code is further linked and loaded to generate the executable.
Source code  Compile  loader/linker  executable code
Object code
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5. C program structure Program Directives (#include libraries) functions
statements
Variables/constants
Different types of statements
Sequential, assignment, selection,
iterative, input/output
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6. Variables and arithmetic expressions
#include <stdio.h>
/* print Fahrenheit-Celsius table
for fahr = 0, 20, ..., 300 */
main() {
int fahr, celsius;
int lower, upper, step;
lower = 0; /* lower limit of temperature scale */
upper = 300; /* upper limit */
step = 20; /* step size */
fahr = lower;
while (fahr <= upper) {
celsius = 5 * (fahr-32) / 9;
printf("%d\t%d\n", fahr, celsius);
fahr = fahr + step; }
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9/18/2018

7. Lets analyze the program
#include directive
Comment // single line comment
/* multiple line
comment */
3. Main function
4. Variable declarations {variable type, variable name}
int step;
5. Initialization: step= 20;
6. Statements: computations; arithmetic operations {+, -, *, /, %}
7. Repeat computation using a “while loop”
8. Condition for repetition
9. Output results using “printf”
10. Semicolon (;) as a terminator for statements
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8. Variable types int: integer; for representing whole numbers
float : floating point or real numbers; for representing fractional numbers, vary large and very small numbers (32 bits)
double: double precision real number; double the size of float (64 bits)
char: single ASCII (American Standard Code of Information Interchange) character
long: longer integer
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9. Variable names
A sequence of characters used for identifying an entity/item used in the program
Example:
partNum
voltage
portNum
myName
ECUNum
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10. Assignment statement Assignment operator = Syntax
Variable = expresion;
partNum = 84560;
double temp = 89.5;
int age = 78;
pay = salary + bonus;
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9/18/2018

11. Arithmetic operators Addition + Subtraction – Multiplication *
Division /
Modulus %
Precedence of operators:
*, /, %
+ -
Left to right associavity
Override precedence using ( )
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9/18/2018

12. Arithmetic expression
celsius = 5 * (fahr-32) / 9;
3 + 5 – 10 * 2 / 3 % 4
= /3 % 4
= – 6% 4
= 3+5 – 2
= 8 – 2
= 6
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13. Iteration/repetition
While loop
Syntax:
Initialize condition;
while (condition)
{ statements;
update condition; }
Execution semantics
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9/18/2018

14. If..else: selection
Often we need to make choices in the execution path.
If ..else statement
if (sensedTemp > refTemp)
//cool the room
else
if (sensedTemp < refTemp)
// heat the room
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9/18/2018

15. Multi-way selection Case or switch statement: switch (grade) {
case ‘A’ : printf (“Very good \n”); break;
case ‘B’ : printf (“Good\n”); break;
case ‘C’ : printf(“not bad\n”); break;
case ‘F’: printf(“Bad\n”);
default: printf(“Grade out of range \n”); }
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9/18/2018

16. Putting it all together
Lets solve the problem below using C.
Consider the number game shown in the next few slides.
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17. The Number Game (1) 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
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18. The Number Game (2) 2 3 6 7 10 11 14 15 18 19 22 23 26 27 30 31
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19. The Number Game (4) 4 5 6 7 12 13 14 15 20 21 22 23 28 29 30 31
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20. The Number Game (8) 8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31
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21. The Number Game (16) 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
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22. Analysis What is theory /concept behind this game?
How did I arrive at the number you guessed?
How can I automate this process?
What is the data and what is the algorithm?
How can we convey these to a computing machine?
While a computer talks binary, we humans write programs in languages such as Java, C#, C++, Basic etc.
Binary numbers (1’s and 0’s) is the number system used by the computer systems.
We humans use decimal number system that has 10 distinct symbols (0,1,2,3,4,5,6,7,8,9)
Your task: Write a C program to computerize this game.
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23. 2 3 6 7 10 11 14 15 18 19 22 23 26 27 30 31 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 4 5 6 7 12 13 14 15 20 21 22 23 28 29 30 31 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 8 9 10 11 12 13 14 15 24 25 26 27 28 29 30 31
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24. Ch.4 in Kernighan and Ritchie C textbook
C Language: Functions
Ch.4 in Kernighan and Ritchie C textbook
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25. Topics Purpose of functions Function design Function definition
Function call
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26. Functions
Functions are modular units that perform a specific operation
It provides the ability to divide the program into coherent modules
Functions can be parameterized providing a general solution that can be customized with specific parameters
Functions offers a method for spreading the code around many files, thus providing a method for organization of code (into libraries, say)
Once defined, a function can be called from anywhere accessible and any number of times resulting in reusability, standardization and uniform application of operations
cse
9/18/2018

27. Function Design
Lets say you want to turn Fahrenheit to Celsius converter into a function rather than dumping all the code in the main function.
Value in C
Value in F
celf
fcel
Converted value in C
Converted value in F
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9/18/2018

28. Function Definition Define the prototype
Type function name (parameter type, parameter type…);
Define the header
Return type function name (param type name, param type name…)
Define the body of the function
{ local variable
statements
one or more return statements}
Example:
float fcel (float);
float fcel (float fah) {
float celsius = (5.0/9.0) * (fah );
return celsius; }
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9/18/2018

29. Function Call
It is not enough defining the function: it needs to be activated.
This is done by calling the function.
Calling a function involves specifying its name and actual parameter values. If there is a return value the call needs to be assigned to a variable.
Example
float fahren = 35.0;
float celsius = fcel(fahren);
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30. Complete Example Lets write another function for Celsius to Farenheit.
float celf (float celsi) {
float fahr = celsi * 9.0/ ;
return fahr; }
Call:
float fa = celf (35.0);
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9/18/2018

31. Demos
Lets add an input statement to the functions and complete the example.
Scanf is the input statement. You provide the format(type) as well as the location (address) with name the input will be loaded into.
Example:
scanf(“%f”, &celsi);
scanf(“%f”, &fahr);
celsi
fahr
cse
9/18/2018

32. Summary We studied basics of a function design.
We learned function definition and function call.
Standard IO using printf and scanf was also illustrated.
Parameter passing by value and reference was introduced. We will discuss this in detail later.
There is lot more C language: pointers, memory management (allocation, deallocation, etc.) memory leaks, struct, separate compilation, makefile… ( we will discuss all these.)
cse
9/18/2018