LAB 6 FUNCTION PART 1 School of Computer and Communication Engineering Universiti Malaysia Perlis

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1 Laboratory Module [Updated October 2017] LAB 6 FUNCTION PART 1 School of Computer and Communication Engineering Universiti Malaysia Perlis 1

2 OBJECTIVES 1. To differentiate between predefined function and user-defined function. 2. To identify different components in a C program function. 3. To identify types of arguments and return value. 4. To differentiate call by value and call by reference. NOTES Part 1 Introduction to function 1. A C program is generally formed by a set of functions, which subsequently consists of many programming statements. Using functions, large computing tasks can be broken into smaller ones. The core concepts of C functions are reusability i.e. dividing a big task into small pieces to achieve the functionality and to improve understandability of a very large program. 2. C functions can be categorized into predefined functions and user defined functions. i. Library functions are those functions which are already defined in C library, example printf(), scanf(), strcat() etc. You just need to include appropriate header files to use these functions e.g. stdio.h, string.h and math.h. These are already declared and defined in C libraries. ii. User-defined functions are those functions which are defined by the user at the time of writing program. Functions are made for code reusability and for saving time and space. 2

3. The benefits of using functions are:- i. It provides modularity to the program. ii. It helps in code reusability. You just have to call the function by its name to use it. iii.

3 3. The benefits of using functions are:- i. It provides modularity to the program. ii. It helps in code reusability. You just have to call the function by its name to use it. iii. In case of large programs with thousands of code lines, debugging and editing becomes easier if you use functions. iv. It makes the program easier to design and understand. Part 2 User-defined function i. There are 3 components in a user-defined function:- i. Function declaration or prototype This informs compiler about the function name, function parameters (arguments) and return value s data type. ii. Function call This calls the actual function iii. Function definition This contains all the statements to be executed. Figure 1 Components of a C function (Source: 3

$h> int a = 10, b = 5, c; int main() c = a * b; //product printf("a * b = %i\n",c); c = a + b; //sum printf("a + b = %i\n",c); return 0; #include <stdio.$

4 Figure 2 Function definition (Source: Table 1 Comparison of a program with and without function A program without function A program with a function #include <stdio.h> int a = 10, b = 5, c; int main() c = a * b; //product printf("a * b = %i\n",c); c = a + b; //sum printf("a + b = %i\n",c); return 0; #include <stdio.h> int a = 10, b = 5, c; int product(int, int); int main() c = product(a,b); printf("a * b = %i\n",c); c = sum(a,b); printf("a + b = %i\n",c); return 0; int product(int x,int y) return x * y; int sum(int x,int y) return x + y; 4

5 [Updated October 2017] Laboratory Module Part 3 Function arguments and return value All C functions can be called either with arguments or without arguments in a C program. These functions may or may not return values to the calling function. There are:- i. C function with arguments (parameters) and with return value. ii. C function with arguments (parameters) and without return value. iii. C function without arguments (parameters) and without return value. iv. C function without arguments (parameters) and with return value. Table 2 Different types of arguments and return value Types Syntax example 1. With arguments and return value //function declaration int function ( int ); 2. With arguments and without return value //function call function ( a ); //function definition int function( int a ) statements; return a; //function declaration void function ( int ); //function call function( a ); //function definition void function( int a ) statements; int square(int); //function declaration void main() int result, num = 9; result = square(num); //function call printf("square of %d is %d\n",num,result); int square(int x) //function definition return x*x; void square(int); //function declaration void main() int num = 9; square(num); //function call void square(int x) //function definition int result = x*x; printf("square of %d is %d\n",x,result); 5

6 3. Without arguments and without return value 4. Without arguments and with return value //function declaration void function(); //function call function(); //function definition void function() statements; //function declaration int function ( ); //function call function ( ); //function definition int function( ) statements; return a; void square(void); //function declaration void main() square(); //function call void square(void) //function definition int x = 9; int result = x*x; printf("square of %d is %d\n",x,result); int square(void); //function declaration int x = 9;//global variable void main() int result = square(); //function call printf("square of %d is %d\n",x,result); int square(void) //function definition return x*x; NOTE: If the return data type of a function is void, then, it can t return any values to the calling function. If the return data type of the function is other than void such as int, float, double etc, then, it can return values to the calling function. 6

7 Laboratory Module [Updated October 2017] Part 4 Call by value vs. call by reference There are two ways that a C function can be called from a program. i. Call by value - the value of the variable is passed to the function as parameter. //function declaration or prototype void swap(int, int); int main() int x = 20, y = 5; printf("\nvalues before swap x = %d and y = %d\n", x,y); swap(x,y); //function call return 0; void swap(int a, int b) //function definition int tmp; tmp = a; a = b; b = tmp; printf("\nvalues after swap x = %d and y = %d\n", a,b); Sample output: Values before swap x = 20 and y = 5 Values after swap x = 5 and y = 20 7

8 ii. Call by reference - the address of the variable is passed to the function as parameter. //function declaration or prototype Sample void swap(int output: *, int *); int main() int x = 20, y = 5; printf("\nvalues before swap x = %d and y = %d\n", x,y); swap(&x,&y); //function call return 0; void swap(int *a, int *b)//function definition int tmp; tmp = *a; *a = *b; *b = tmp; printf("\nvalues after swap x = %d and y = %d\n", *a,*b); Sample output: Values before swap x = 20 and y = 5 Values after swap x = 5 and y = 20 8

9 EKT 120 Introduction to Computer Programming Laboratory Module PART 1- ERRORS TRACING Identify and correct errors in the following program segments:- i. int fun(double x); //function prototype int fun(int x)) //function definition return 5 * x; ii. float fun(float x) //function definition return 3*3; fun(3,3); //function call iii. void fun1(float x); //function prototype int fun1(int x) //function definition float y; y = 3 * x; return y; iv. int total(int x, int y) //function definition return x + y; void fun(int x, int y) //function definition int total; total = total(x,y); 9

10 EKT 120 Introduction to Computer Programming Laboratory Module PART 2-DISPLAY OUTPUT i. Predict and write the output for the program shown in Figure 3. #include <stdio.h> int fnsubstitute (int this, int that); void main() int ix = 3, iy = 7; ix =fnsubstitute (ix, iy); printf("%4d%4d\n", ix, iy); int fnsubstitute(int this, int that) int iz = 5; that = 3 + iz; this = iz * that; return(this); Figure 3 ii. Write the output after executing the program segment in Figure 4. int func (int a, int b) a -= 1; printf("a = %d, b = %d.\n", a, b); return a-- * ++b; int sub (int *a, int *b) *a += 9; printf("a = %d, b = %d.\n", *a, *b); return ++*a + --*b; int main() int x = 6, y = 8; y = func(x, y); printf("x = %d, y = %d.\n", x, y); y = sub(&x, &y); printf("x = %d, y = %d.\n", x, y); return 0; Figure 4 10

11 EKT 120 Introduction to Computer Programming Laboratory Module iii. Consider the program given in Figure 5, write the output of the program. #include <stdio.h> void function1(int Num1, int Num2) printf("\ninside Function 1\n"); Num1=Num1+Num2; Num2=Num2+Num1; printf ("Num1=%d\tNum2=%d\n\n",Num1,Num2); void function2(int *Num1, int* Num2) printf("\ninside Function 2\n"); *Num1=*Num1+*Num2; *Num2=*Num2+*Num1; printf ("Num1=%d\tNum2=%d\n\n",*Num1,*Num2); int main () int A=10, B=20; printf ("A=%d\tB=%d",A,B); function1(a,b); printf("in main\n"); printf ("A=%d\tB=%d",A,B); function2(&a,&b); printf("in main\n"); printf ("A=%d\tB=%d",A,B); Figure 5 PART 3 i. Consider a function definition of fnsum in the program segment given in Figure 6. int fnsum (int inum1,int inum2) int iadd; iadd = inum1 + inum2; return(iadd); Figure 6 11

12 EKT 120 Introduction to Computer Programming Laboratory Module (a) Identify and write the function name (b) Identify and write the function prototype (c) Write the function call assuming that Num1 and Num2 were already declared as integer. (d) Identify and write the data type of what the function returned. ii. Complete the function in Figure 7 which passes the parameters by reference. void fninput ( int, int ) printf( Please input two integer numbers\n ); scanf( %d, ); scanf( %d, ); Figure 7 iii. A program computes volume of a cylinder by requesting user to enter radius in cm and height in cm. The formula to calculate volume of a cylinder is volume = π * radius * radius * height Write a function definition calcvolume : accepts radius and height in order to calculate volume by passing those two arguments by value and return calculation of volume. iv. A program computes perimeter of a parallelogram by requesting user to enter length in cm and width in cm. The formula to calculate perimeter of a parallelogram is perimeter = 2 * (length + width) You are required to write two functions definition as follows: (a) readinput: read input of length and width and pass by reference those two inputs. 12

13 EKT 120 Introduction to Computer Programming Laboratory Module (b) calcperimeter : accepts length and width in order to calculate perimeter by passing those two arguments by value and, return calculation of perimeter by reference. PROGRAMMING QUESTIONS 1. The power consumption of a heater is calculated by the equation p = vi where p = power (watts) v = voltage (volts) i = current (amperes) R = v/i where R = resistance (ohms) Write a C program that computes power and resistance of a heater with inputs of voltage and current. You are required to write three (3) functions as follows: (a) read_vc : read voltage and current and pass both arguments by reference (b) calc_power_resistance : compute power and resistance; receives arguments voltage and current and pass arguments power and resistance by reference (c) display_power_resistance : print voltage, current, power and resistance Sample output is described in Figure 8. Enter voltage and current: Input voltage = volts, current = 5.50 amperes Power consumed by the heater = watts Heater resistance = ohms Figure 8 2. Write a program of function to return the volume of a sphere with the input argument for the radius of the sphere. The formula for the volume of sphere is πr3, where r is the radius of the sphere. Test your program with a radius of 5 meters. 3. Write a program that calculates the area and perimeter of a rectangle. The area and perimeter are calculated using two separated functions, which both take two arguments of a float type for the width and length of the rectangle. Calculate the area and perimeter using these two functions in the main program for a rectangle with width and length of 2.5 cm and 5.5 cm, respectively. 13

LAB 6 FUNCTIONS I School of Computer and Communication Engineering

LAB 6 FUNCTIONS I School of Computer and Communication Engineering 1 Universiti Malaysia Perlis 1. OBJECTIVES: 1.1 To apply functions as building blocks of programs. 1.2 To write C programs using functions.