COM 241 Programming Languages Concepts Assoc Prof Dr

COM 241 Programming Languages Concepts Assoc. Prof. Dr. Mehmet Serdar Güzel Slides are mainly adapted from the following course page: http: //www. cs. utexas. edu/~shmat/courses/cs 345/ • slid e 1

COM 241 Functions slide 2

Functional Abstraction A function is a block of organized, reusable code that is used to perform a single, related action. Functions provide better modularity for your application and a high degree of code reusing. You have already seen various functions like printf() and main(). These are called built-in functions provided by the language itself, but we can write our own functions as well and this tutorial will teach you how to write and use those functions in C programming language. Value-returning functions Example: m = sqrt(4*a*c))/2 Non-value returning functions Called “procedures” (Ada), “subroutines” (Fortran), “void functions/methods” (C, C++, Java, C#) Have a visible side effect: change the state of some data value not defined in the function definition Example: strcpy(a 1, a 2) slide 3

System Calls A system call is a way for programs to interact with the operating system. A computer program makes a system call when it makes a request to the operating system's kernel. slide 4

Arguments && Parameters Argument: expression appearing in a function call Parameter: identifier appeared in function declaration Parameter-argument matches by considering number and position Exception: Perl. slide 5

Parameter Passing Mechanisms Call By value Call By reference Call By value-result Call By name slide 6

Pass by Value vs Reference Pass by value means you are making a copy in memory of the actual parameter's value that is passed in, a copy of the contents of the actual parameter. Pass-by-reference means to pass the reference of an argument in the calling function to the corresponding formal parameter of the called function slide 7

Two Ways To Pass By Reference C or C++ only void swap (int *a, int *b) { int temp = *a; *a = *b; *b = temp; } void swap (int& a, int& b) { int temp = a; a = b; b = temp; } int a=13, b=14; swap(&a, &b); int a=13, b=14; swap(a, b); Which one is better? slide 8

Pass by Value-Result Pass by value at the time of the call and/or copy the result back to the argument at the end of the call (copy -in-copy-out) Example: “in out” parameters in Ada slide 9

Pass by Value-Result Refered by http: //courses. cs. vt. edu/cs 3304/Fall 16/meng/lecture_notes/cs 3304 -16. pdf slide 10

Pass by Name Textually substitute the argument for every instance of its corresponding parameter in the function body Originated with Algol 60 but dropped by Algol’s successors -- Pascal, Ada, Modula slide 11

Pass by Name Refered by http: //courses. cs. vt. edu/cs 3304/Fall 16/meng/lecture_notes/cs 3304 -16. pdf slide 12