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  • Begin the session by explaining the objectives of the session.
  • Give an example where you need to use a function for reusability.
  • Tell the students that a parameter is a means by which functions pass information.
  • Use this slide to test the student’s understanding on parameters.
  • Tell the students that calling a function is termed as invoking a function. A function is invoked or called by writing the function name with parameters, if any. Also discuss actual parameters and formal parameters. What is implemented in C is not a true call by reference. A call by reference actually involves providing an alias for the original variable being referenced. There should be no difference in the way the original variable and the referencing variable is used (even in the syntax). What happens in C is that the address of the variable is passed. This address is received into a pointer and the pointer is dereferenced. Here a local variable (the pointer) is created in the called function. In a true call by reference , a variable is not created.
  • Use this slide to test the student’s understanding on call by value and call by reference.
  • As parameters are used to pass the required information to the called function, similarly, the return statement is used to pass the result back to the calling function.
  • Use this slide to test the student’s understanding on returning values from a function.
  • Explain command-line arguments to the students. Give the example of the copy command in MS DOS. Tell the students that copy is the command and the name of the source and the target file are the arguments to the copy command. The command-line arguments are separated by a space.
  • Use this slide to test the student’s understanding on command-line arguments.
  • Tell the students that if they want to ignore case while comparing two strings, they can use the strcmpi() function.
  • Use this slide to test the student’s understanding on string-handling functions.
  • Use this slide to test the student’s understanding on string to numeric conversion functions.
  • Use this slide to test the student’s understanding on sscanf() and sscanf() functions.
  • Use this slide to test the student’s understanding on data storage types .
  • Use this slide to test the student’s understanding on data storage types .
  • Use this and the next 2 slides to summarize the session.

C programming session 08 Presentation Transcript

  • 1. Programming in CObjectives In this session, you will learn to: Implement modular approach in C programs Use library functions for string manipulation Work with data storage types Ver. 1.0 Slide 1 of 44
  • 2. Programming in CImplementing Modular Approach in C Programs • Functions are the building blocks of C. • Every C program must consist of at least one function, main(). • The main() function is the entry point of a C program. Ver. 1.0 Slide 2 of 44
  • 3. Programming in CAdvantages of Functions Functions: Allow reusability of code and structuring of programs. Provide programmers a convenient way of designing programs. Ver. 1.0 Slide 3 of 44
  • 4. Programming in CParameters of Functions A parameter: Is the data that the function must receive when called from another function. May or may not be present in a function. Of a user-defined function is declared outside the {} of that function. Ver. 1.0 Slide 4 of 44
  • 5. Programming in CPractice: 5.1 • From the following program, identify the functions invoked from main(), and state which functions have parameters. Also state the parameters. Microsoft Office Word 97 - 2003 Document Ver. 1.0 Slide 5 of 44
  • 6. Programming in CPractice: 5.1 (Contd.) Solution: – The standard functions used in this program within main() are as follows: scanf() – parameters are format of input, and pointers to the variable(s) in which the input must be stored fflush() – parameter is stdin The user-defined functions are: output() – no parameters calc() – one parameter, g, an int type data Ver. 1.0 Slide 6 of 44
  • 7. Programming in CInvoking Functions Functions that have parameters are invoked in one of the following ways: Call by value: In call by value, the called function cannot refer to the variables of the caller function directly, but creates its own copy of the values in different variables. Call by reference: In call by reference, the called function should be able to refer to the variables of the caller function directly, and does not create its own copy of the values in different variables. It is possible only if the addresses of the variables are passed as parameters to a function. Ver. 1.0 Slide 7 of 44
  • 8. Programming in CPassing Arrays to Functions Arrays are inherently passed to functions through call by reference method. An array can be passed to a function in the following way: Function name (array name); Ver. 1.0 Slide 8 of 44
  • 9. Programming in CPractice: 5.2 • If the variable avar is passed to a function by a call by reference, can the value of the variable avar be modified in the called function? Give reasons for your answer. • State whether True or False: When an array is passed to a function, the array elements are copied into the parameter of the function. 3. Consider the program code given in the following file. Microsoft Office Word 97 - 2003 Document Ver. 1.0 Slide 9 of 44
  • 10. Programming in CPractice: 5.2 (Contd.) Based on the code, answer the following questions: a. The function (max() / min()) is invoked by a call by value. b. The function (max() / min()) is invoked by a call by reference. c. After the function max() is executed, where does the control go to: i. The min() function. ii. The first line of the main() function. iii. The first line of the main() following the line on which max() was invoked. d. After execution of the function min(), program execution: i. Stops without returning to main(). ii. Goes back to the main() function. – If the values of i and j were to be printed after the function max() and again after the function min(), what values would be displayed? Ver. 1.0 Slide 10 of 44
  • 11. Programming in CPractice: 5.2 (Contd.) • Write a program that calls a function called power(m,n), which displays the nth power of the integer m (m and n are parameters). The function must be invoked by a call by reference. Ver. 1.0 Slide 11 of 44
  • 12. Programming in CPractice: 5.2 (Contd.) Solution: – Yes, because the addresses of the variables are passed in by using call by reference, the memory locations of the variables are known to the function. Using pointers to the variables, their values can be modified. – False. Values of variables are copied into the parameters only in the case of a call by value. – a. max() b. min() c. iii d. ii e. After max() is executed, the values of i and j printed out would be the same as those entered during execution. After min() is executed, the value of i would still be the same, but j would increase by 5 (since b is a pointer to the variable j). Ver. 1.0 Slide 12 of 44
  • 13. Programming in CPractice: 5.2 (Contd.) 1.main() { int x, y; printf(“Enter Number: ”); scanf(“%d”, &x); fflush(stdin); printf(“Enter power raise to : “); scanf(“%d”, &y); fflush(stdin); power(&x, &y); } power(m,n) int *m, *n; /* power is pointed to by n, value is pointed to by m */ { int i=1,val=1; while(i++<= *n) val = val ** m; printf(“%d the power of %d is %dn”, *n,*m, val);} Ver. 1.0 Slide 13 of 44
  • 14. Programming in CReturning Values from a Function • A function can return a value to the caller function. • The return statement is used to send back a value to the caller function. • The return statement also transfers control back to calling function. • The default return value is int type. • The return statement can return only one value. • The syntax for the return statement is: return[expression] A function can also return an array. This could be done by: return [array name] Ver. 1.0 Slide 14 of 44
  • 15. Programming in CPractice: 5.3 1. Point out the error(s), if any, in the functions given in the following file: Microsoft Word Document 5. The following program should calculate the square of any float value, using a function called square(). The float value is an input to the program. The program is incomplete. Put in the appropriate statements in the program given in the following file: Microsoft Word Document Ver. 1.0 Slide 15 of 44
  • 16. Programming in CPractice: 5.3 (Contd.) • The function, makeint(), was coded to convert any number entered into a char array to integer type. The function takes the string as parameter and returns the value, as given in the following file: Microsoft Word Document Ver. 1.0 Slide 16 of 44
  • 17. Programming in CPractice: 5.3 (Contd.) Solution: Microsoft Word Document Ver. 1.0 Slide 17 of 44
  • 18. Programming in CCommand-Line Arguments Command-line arguments: – Are the parameters that the main() function can receive from the command line. – Are passed as information from the OS prompt to a program. • The main() function has 2 arguments, argc and argv. The format of the main() function with parameters is as follows: main(argc, argv) int argc; char *argv[]; { : } Here, argc is integer and argv is a character array of unlimited size (hence [ ] in the declaration). Ver. 1.0 Slide 18 of 44
  • 19. Programming in CPractice: 5.4 1. Given that a C program called temp is executed by the following command: temp start 6 match the following: a. value of argc 1. points to array "6" b. argv [0] 2. points to arrm/ "start" c. argv [1] 3. 3 d. argv[2] 4. points to array "temp" 2. Modify the program upper so that it first checks the number of arguments entered on the command line. The program should display an error message if no arguments have been entered and also allow conversion of as many strings to upper-case as have been specified as arguments on the command line. Ver. 1.0 Slide 19 of 44
  • 20. Programming in CPractice: 5.4 (Contd.) 3. Consider the following program to calculate the sum of 2 integers specified on the command line: main (argc, argv) int argc; char *argv [ ];{ sum (argv [1], argv [2]); } sum (num1, num2) int numl, num2;{ return numl + num2; } The program has some logical errors. Point out the errors and correct the code. Ver. 1.0 Slide 20 of 44
  • 21. Programming in CPractice: 5.4 (Contd.) Solution: Microsoft Word Document Ver. 1.0 Slide 21 of 44
  • 22. Programming in CUsing Library Functions for String Manipulation Library functions: Are also known as built-in functions. Can be used by including the concerned header files. Ver. 1.0 Slide 22 of 44
  • 23. Programming in CStandard String-Handling Functions Some of the standard string-handling functions are: – strcmp(): Compares 2 strings (its parameters) character by character (ASCII comparison). – strcpy(): Copies the second string to the first string named in the strcpy() parameters. – strcat(): Appends the second string passed at the end of the first string passed to it . – strlen(): Returns the number of characters in the string passed to it. Ver. 1.0 Slide 23 of 44
  • 24. Programming in CPractice: 5.5 1. What will the following function call return? x = strcmp(“Cada”, “CADA”); What should the declaration of x be? 4. Assume that array contains the string 846*. What will array contain when the following statement is executed? strcat(array,”>”); 7. State whether True or False: The following statement returns a value of 4 to x. x = strlen ("abc"); Ver. 1.0 Slide 24 of 44
  • 25. Programming in CPractice: 5.5 (Contd.) Solution: 1. Value returned - 32 Declaration - int x; 3. 846*> 4. False Ver. 1.0 Slide 25 of 44
  • 26. Programming in CString to Numeric Conversion Functions Conversion functions: Are available as a part of the standard library. Are used to convert one data type into another. The following functions are used to convert a string to a numeric value: – atoi(): Returns the int type value of a string passed to it and the value 0 in the case the string does not begin with a digit. – atof(): Returns the double type value of a string passed to it and the value 0 in the case the string does not begin with a digit or a decimal point. Ver. 1.0 Slide 26 of 44
  • 27. Programming in CPractice: 5.6 • What value will the variable val contain in each of the following situations? a. val = atoi ("A345"); /* val is int type */ b. val = atof ("345A"); /* val is double type */ Ver. 1.0 Slide 27 of 44
  • 28. Programming in CPractice: 5.6 (Contd.) Solution: 1. a. 0 b. 345.000000 Ver. 1.0 Slide 28 of 44
  • 29. Programming in CFunctions for Formatting Data in Memory The formatting functions are available as a part of the standard library. The following functions are used to format data in memory: sprintf(): Writes to a variable in the memory and stores the data in different variables specified. Are used for transferring data between variables in a specific format. Has the following syntax: sprintf(string, format-specification, data, ….); sscanf(): Performs formatted input from a string. Has the following syntax: sscanf(string, format-specification, data, ….); Ver. 1.0 Slide 29 of 44
  • 30. Programming in CPractice: 5.7 1. What data is assigned to the variable string by each of the following? a. sprintf(string,"%04d%3.2f%2s",21,4.576, "Hi“); b. sprintf (string, "%10s", "ABC"); c. sscanf ("0987APZ", "%4d%s", &num, string); 2. What is the error, if any, in the instructions given below against each purpose? Give the correct instruction in case of an error. Purpose Instruction Accept a name from keyboard printf(“%s”, name); Format the contents of variables printf (string,"%d%f, i_num,f_num) i_num(int) and f_num(float), and store them into a character array called string. Ver. 1.0 Slide 30 of 44
  • 31. Programming in CPractice: 5.7 (Contd.) Solution: Microsoft Word Document Ver. 1.0 Slide 31 of 44
  • 32. Programming in CWorking with Data Storage Types C language provides the following data storage types: – auto: Variables of this type retain their value only as long as the function is in the stage of execution. – static: Variables of this type retain its value even after the function to which it belongs has been executed. – extern: Variables of this type are declared at the start of the program and can be accessed from any function. Ver. 1.0 Slide 32 of 44
  • 33. Programming in CPractice: 5.8 1. Given the following declarations: float area; static float val; auto char number; State which variable(s) will be: a. Created each tune the function is invoked. b. Created only once. 2. A numeric array has to store 4 values - 2.5, 6,3, 7.0 and 8.0. This array is to be declared and used in a function called compute(). Which of the following is/are correct declarations of this array? a. static int values[4] = {2.5,6.3,7.0,8.0}; b. auto float values[4] = {2.5,6.3,7.0,8.0 }; c. float values [4]= {2.5,6.3,7.0,8.0}; d. static float values [4] = {2.5,6.3,7.0,8.0}; Ver. 1.0 Slide 33 of 44
  • 34. Programming in CPractice: 5.8 (Contd.) Solution: 1. a. area, number b. val 3. (a) Is invalid because the array should be float or double type. (b) Is invalid because it is declared as auto type. (c) Is invalid because it is declared as auto type. (d) Is correct. . Ver. 1.0 Slide 34 of 44
  • 35. Programming in CPractice: 5.9 • If the variable val is declared as global in the program B, just illustrated, how would program A be modified? Give the appropriate declarations required in both programs. • Consider the following 2 program files: Program A float x; calc() { int i; : } printout() { static char z; : } Program B char numarray[5]; main() { char c ; : } Ver. 1.0 Slide 35 of 44
  • 36. Programming in CPractice: 5.9 (Contd.) Based on this code, answer the following: a. The variable z can be accessed in the function(s) ____________________. b. The variable(s) that can be accessed from functions of both program files is/are ___________. c. Slate whether True or False: The variable i can be used in the function printout(). d. Memory for variable z is reserved each time the function printout() is invoked. State whether true or false. e. If the function printout() has to access the variable x, does x have to be declared within the function printout()? If so, give the declaration. f. The auto variable(s) in these programs is/are _________________. Ver. 1.0 Slide 36 of 44
  • 37. Programming in CPractice: 5.9 (Contd.) Solution: 1. In program B, val would be declared as follows: int val; calc(){ :} In program A, the declaration would be as follows: main() { extern int val; :} – a. printout() only (Since it is declared within the function printout() and hence is not global) x and numarray (if proper extern statements are coded). b. False (Since it is declared within the function calc(), and hence it is not global) Ver. 1.0 Slide 37 of 44
  • 38. Programming in CPractice: 5.9 (Contd.) c. False (Since z is a static variable, it is created only once – the function printout() is invoked.) d. No (Since x is declared as global in program A, and printout() is defined in the same program file. However, declaring it as extern while within printout() is wrong.) e. The variable i defined in calc() and the variable c defined in main(). Ver. 1.0 Slide 38 of 44
  • 39. Programming in CPractice: 5.10 • The following file contains a C program called remdigit.c and a list of errors in the program indicated by the compiler. Go through the error list and correct the program. Since the C compiler does not always give very meaningful error messages, go through the program given in the following file carefully. Microsoft Office Word 97 - 2003 Document Ver. 1.0 Slide 39 of 44
  • 40. Programming in CPractice: 5.10 (Contd.) • Write a program to display all the positions at which a character occurs in a string. Both the character to be located and the string to be searched should be passed to a function called nextpos (findchar, searchstr). Each time the function locates the diameter, it should pass back the position. After searching the entire string, the function should return the value -1. Ver. 1.0 Slide 40 of 44
  • 41. Programming in CPractice: 5.10 (Contd.) Solution: Work out your answers. A discussion on these follows in the Classroom. Ver. 1.0 Slide 41 of 44
  • 42. Programming in CSummary In this session, you learned that: Functions provide advantages of reusability and structuring of programs. A parameter of a function is the data that the function must receive when called or invoked from another function. Functions that have parameters are invoked in one of the following two ways: • Call by value • Call by reference – Call by value means that the called function creates its own copy of the values in different variables. – Call by reference means that the called function should be able to refer to the variables of the caller function directly, and does not create its own copy of the values in different variables. Ver. 1.0 Slide 42 of 44
  • 43. Programming in CSummary (Contd.) – Arrays are passed to functions by the call by reference method. – Functions can return values by using the return statement. – The main() function can have parameters, argc and argv. argc is integer type while argv is a string. – The information that is passed to a program from the OS prompt is known as command-line arguments. – Some of the standard string-handling functions are: • strcmp(): Compares two strings. • strcpy(): Copies the second string to the first string. • strcat(): Appends the second string passed at the end of the first string passed as parameters. • strlen(): Returns the number of characters in the string passed as a parameter. Ver. 1.0 Slide 43 of 44
  • 44. Programming in CSummary (Contd.) • atoi(): Returns the int type value of a string passed to it. • aof(): Returns the double type value of a string passed to it. – The following functions are used to format data in memory: sprintf() sscanf() – C language provides the following data storage types: • auto: Variables of this type retain their value only as long as the function is in the stage of execution. • static: Variables of this type retain its value even after the function to which it belongs has been executed. • extern: Variables of this type are declared at the start of the program and can be accessed from any function. Ver. 1.0 Slide 44 of 44