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The C Language

The C Language. B. Ramamurthy University at Buffalo bina@buffalo.edu. 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.

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The C Language

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  1. The C Language B. Ramamurthy University at Buffalo bina@buffalo.edu cse321-2013-3

  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. cse321-2013-3

  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; } cse321-2013-3

  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 cse321-2013-3

  5. C program structure Program Directives (#include libraries) functions statements Variables/constants Different types of statements Sequential, assignment, selection, iterative, input/output cse321-2013-3

  6. Variables and arithmetic expressions #include <stdio.h> /* print Fahrenheit-Celsius table for fahr = 0, 20, ..., 300 */ main() { intfahr, 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; } } cse321-2013-3

  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 cse321-2013-3

  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 cse321-2013-3

  9. Variable names A sequence of characters used for identifying an entity/item used in the program Example: partNum voltage portNum myName ECUNum cse321-2013-3

  10. Assignment statement Assignment operator = Syntax Variable = expresion; partNum = 84560; double temp = 89.5; int age = 78; pay = salary + bonus; cse321-2013-3

  11. Arithmetic operators • Addition + • Subtraction – • Multiplication * • Division / • Modulus % • Precedence of operators: • *, /, % • + - • Left to right associavity • Override precedence using ( ) cse321-2013-3

  12. Arithmetic expression • celsius = 5 * (fahr-32) / 9; • 3 + 5 – 10 * 2 / 3 % 4 =3 + 5 -20 /3 % 4 = 3 + 5 – 6% 4 = 3+5 – 2 = 8 – 2 = 6 cse321-2013-3

  13. Iteration/repetition While loop Syntax: Initialize condition; while (condition) { statements; update condition; } Execution semantics cse321-2013-3

  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 cse321-2013-3

  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”); } cse321-2013-3

  16. Putting it all together Lets solve the problem below using C. Consider the number game shown in the next few slides. cse321-2013-3

  17. The Number Game (1) cse321-2013-3

  18. The Number Game (2) cse321-2013-3

  19. The Number Game (4) cse321-2013-3

  20. The Number Game (8) cse321-2013-3

  21. The Number Game (16) cse321-2013-3

  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. cse321-2013-3

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  24. C Language: Functions Ch.4 in Kernighan and Ritchie C textbook cse321-2013-3

  25. Topics Purpose of functions Function design Function definition Function call cse321-2013-3

  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 cse321-2013-3

  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 F Converted value in C cse321-2013-3

  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 - 32.0); return celsius; } cse321-2013-3

  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); cse321-2013-3

  30. Complete Example Lets write another function for Celsius to Farenheit. float celf (float celsi) { float fahr = celsi * 9.0/5.0 + 32.0; return fahr; } Call: float fa = celf (35.0); cse321-2013-3

  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 cse321-2013-3

  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.) cse321-2013-3

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