Lecture-3 Functions and Recursion

C Preprocessor Includes header files like stdio.h Expands macros defined Handles conditional compilations PreprocessorProcessor prog.c a.out

Example #include #define PI int main() { float rad=0.0; printf(“Enter the radius of Circle: “); scanf(“%f”, &rad); #ifdef chk_rad if(rad<0) {printf(“Error!\n”); return 1;} #endif printf(“Area of Circle= %f”, PI*rad*rad); return 0; }

Functions “Subprograms” with parameters, program statements, and a result Break code into simpler pieces Promote “reuse” of code in both the same and other programs Link to code written in other programming languages

Prototypes and Definitions Prototypes tell the compiler to expect a function with the specified signature Definition also includes the body of the function May have more than one parameter Follow this link to the program func.cfunc.c

Miscellaneous Libraries included in the C programming environment are a collection of header files, e.g. stdio.h, math.c, etc. Functions not taking any parameters should use keyword “void” in the parameter list Functions with no return type should use return type of “void”

Variable scope Only one function is active in the memory at any time Thus it may use only those variables that it declares Functions can re-declare the same variables within its scope

In-class exercise 3-1 Write a program which finds the largest number from three numbers given to it The main function will prompt the user for three numbers and pass them onto a function which computed the largest The function will return the largest number to the main, which will then print out the result

Call by Value C uses “call by value” to pass parameters between functions by duplicating the values Changing the originally passed parameter in the calling function, does not change the variable value in the called function

Recursion Recursion is when the function calls itself, either directly or indirectly Each recursion has a “base case” which will make the recursion stop. Some conditional statement, like an “if- else” is required to test for the base case for the recursion to stop Follow this link to an example of recursionrecursion

In-class exercise 3-2 Create a program which computes the Greatest Common Divisor for given two numbers Use the method of eigen values Pass the original values to a function The function computes (num1%num2) and recursively calls itself with num2, and the remainder as parameters till the remainder becomes zero(base case!). Then it returns the first parameter as the GCD.

Homework 3 Follow this link to Homework 3Homework 3