UniMAP SemI-09/10EKT120: Computer Programming1 Week 5 – Functions (1)

UniMAP SemI-09/10EKT120: Computer Programming2 Outline Why use functions? Functions in C Pre-defined functions User-defined functions Function prototype Function definition Function call What about number, order and type of parameter? Functions that do not return a value Functions that return a value Miscellaneous about functions Sample application Scope and mechanics of passing values to functions

UniMAP SemI-09/10EKT120: Computer Programming3 Why use functions? Let say you want to print one row of number 8 and one row of number 9 #include int main() {int i, j; //print one row of number 8 for(i=1; i<=10; i++) printf(“8"); printf("\n"); //go to new line //print one row of number 9 for(j=1; j<=10; j++) printf(“9“); printf("\n"); //go to new line return 0; }

UniMAP SemI-09/10EKT120: Computer Programming4 Why use functions?(cont) It seems that you are doing the same thing twice!!(i.e. printing two rows of numbers) This is wasting time and not flexible!! So need to use function

UniMAP SemI-09/10EKT120: Computer Programming5 Why use functions?(cont) #include void display(int); //function prototype int main() { display(8); //function call display(9); //function call return 0; } void display(int value) //function definition { int i; for(i=1; i<=10; i++) printf("%d", value); printf("\n"); //go to new line }

UniMAP SemI-09/10EKT120: Computer Programming6 Functions in C Functions can be created to execute small, frequently-used tasks In C, there are predefined functions or sometimes called standard functions, and there are user- defined functions. Predefined functions are already available functions that can be used, called library The usage is like stdio.h, in which the library name must be #included at the top of the source code (preprocessor directive)

UniMAP SemI-09/10EKT120: Computer Programming7 Predefined function (Library) Common libraries are stdio.h, math.h, string.h, and stdlib.h stdio.h related functions: printf, scanf,etc math.h related functions: sin, cos, exp, pow, sqrt, etc. string.h related functions: strcmp, strcpy, strlen, etc. stdlib.h related functions: abs, fabs

UniMAP SemI-09/10EKT120: Computer Programming8 Predefined function (Library)- example #include void main() { string name; int vol1, vol2, n, R, kTemp, length; strcpy(name, “Marina”); vol2 = vol1 * exp(n * R * kTemp); length = strlen(“Mahathir”); }

UniMAP SemI-09/10EKT120: Computer Programming9 User-defined function What do we need to define and make use of user-defined function? Function prototype Function definition Function call

UniMAP SemI-09/10EKT120: Computer Programming10 Function prototype Function prototype is a declaration; indicates the function exists Should have function name, return type and parameter Argument name is not compulsory in function header Function prototype has the following form: (arg_type arg_name,...); int sum (int num1,int num2); int sum (int,int); //is also acceptable semicolon

UniMAP SemI-09/10EKT120: Computer Programming11 Function definition Function definition includes the body of a function Function definition has the following form: (arg_type arg_name,...) { … statements … } int sum (int num1,int num2) { int add; add = num1 + num2; return(add); }  Notice that argument name is used in the function body  Unlike function prototype, argument name in function definition must be included in function header no semicolon function header

UniMAP SemI-09/10EKT120: Computer Programming12 Function call Consists of a function name followed by an argument expression list enclosed in parentheses Function call has the following form: (exp, exp...) exp is an expression – can be variable or constant result = sum(x,y);

UniMAP SemI-09/10EKT120: Computer Programming13 Example of function in program //This program sums up two numbers #include int sum(int, int); //function prototype int main() { int x,y, result; printf( “Enter x and y : ”); scanf(“%d %d”, &x, &y); result = sum(x,y); //function call printf(“Sum is : %d”, result); return 0; } int sum(int num1, int num2) //function definition { int add; add = num1+num2; return(add);} } function header

UniMAP SemI-09/10EKT120: Computer Programming14 What about number, order and type of parameter? Number, order and type of parameters in the argument list of a function call and function definition MUST match. If function prototype and definition have three parameters then the function call must have three parameters. If the types are int, float and double in the prototype, the types in the function call should be int, float and double, respectively.

UniMAP SemI-09/10EKT120: Computer Programming15 What about number, order and type of parameter?(e.g1) Note that there are two arguments for function prototype, function definition and function call; the first is int and the second is double. With these three we have met the number, order and type requirements.

UniMAP SemI-09/10EKT120: Computer Programming16 What about number, order and type of parameter?(e.g2) int sum(int, int); //function prototype int sum(int num1, int num2) //function definition sum(x,y); //function call Refer to program in slide 13 Number, order and type parameter are met because: there are two parameters, the parameters are listed in order i.e respectively and first parameter is int and second parameter is int.

UniMAP SemI-09/10EKT120: Computer Programming17 Functions that do not return a value //This program sums up two numbers #include void sum_print(int, int); //function prototype void function1(); //function prototype int main() { int x,y; function1(); //function call printf(“Enter x and y: ”); scanf(“%d %d”, &x, &y); sum_print(x,y); //function call return 0; } void sum_print(int num1, int num2) //function definition { int add; add = num1+num2; printf(“Sum is: %d”,add); } void function1() {printf(“Welcome to this program\n”); }

UniMAP SemI-09/10EKT120: Computer Programming18 Functions that return one value //This program sums up two numbers #include int sum(int,int); //function prototype int main() { int x,y,result; printf(“Enter x and y: ”); scanf(“%d %d”, &x, &y); result = sum(x,y); //function call printf(“Sum is : %d”,result); return 0; } int sum(int num1, int num2) //function definition { int add; add = num1+num2; return(add); }

UniMAP SemI-09/10EKT120: Computer Programming19 Miscellaneous about functions Function call used as logical expression int calc(int,int); //function prototype int main(void) {int num1, num2; scanf(“%d %d”,&num1,&num2); if(calc(num1,num2)>100) //function call used as logical expression printf(“result greater than 100”); else printf(“result less than 100”); return 0; } int calc(int n1,int n2) {int answer; answer=n1+n2; return(answer); }

UniMAP SemI-09/10EKT120: Computer Programming20 Miscellaneous about functions Function call used in printf statement int calc(int,int); // function prototype int main(void) {int num1,num2; scanf(“%d %d”,&num1,&num2); printf(“Jawapan : %d”,calc(num1, num2)); //function call returns a //value and puts in printf return 0; } int calc(int n1,int n2) {int answer; answer=n1+n2; return(answer); }

UniMAP SemI-09/10EKT120: Computer Programming21 Miscellaneous about functions Rules regarding naming convention for variables num1 passes value to n1, num2 passes value to n2 Better use different variable names for parameters in main AND parameters in function definition int calc(int,int); //prototype function int main(void) {int num1,num2,result; //declare like this scanf(“%d %d”,&num1,&num2); result = calc(num1,num2); //function call printf(“jawapan : %d“,result); return 0; } //function definition int calc(int n1,int n2) //simply declare like this {int answer; answer=n1+n2; return(answer); }

UniMAP SemI-09/10EKT120: Computer Programming22 Sample application Write a C program that calculates and prints addition and subtraction of numbers. Your program should have functions: add : adds two numbers subtract : subtracts two numbers print_result : prints results from calculation

UniMAP SemI-09/10EKT120: Computer Programming23 Sample application(cont) #include int add(int,int); int subtract(int,int); void print_result(int); int main() {int num1,num2,answer; char op; printf(“Enter two numbers and operator:”); scanf(“%d %d %c”, &num1,&num2,&op); switch(op) {case ‘+’ :answer=add(num1,num2);break; case ‘-’ :answer=subtract(num1,num2);break; default: printf(“Invalid operator”); exit(0); } print_result(answer); return 0; } int add(int x,int y) { int sum; sum = x+y; return(sum); } int subtract(int x,int y) { int sub; sub=x-y; return(sub); } void print_result(int ans) { printf(“Answer is %d”, ans); }

UniMAP SemI-09/10EKT120: Computer Programming24 1. Function prototype (3 parameters)‏ 2. Function call 3. Function definition Program Output 1/* Fig. 5.4: fig05_04.c 2 Finding the maximum of three integers */ 3#include 4 5int maximum(int, int, int); /* function prototype */ 6 7int main()‏ 8{8{ 9 int a, b, c; printf( "Enter three integers: " ); 12 scanf( "%d %d %d", &a, &b, &c ); 13 printf( "Maximum is: %d\n", maximum( a, b, c ) ); return 0; 16} 17 18/* Function maximum definition */ 19int maximum(int x, int y, int z)‏ 20{ 21 int max = x; if ( y > max )‏ 24 max = y; if ( z > max )‏ 27 max = z; return max; 30} Enter three integers: Maximum is: 85

UniMAP SemI-09/10EKT120: Computer Programming25 Scope and Mechanics of Passing Values to Functions Scope refers to the region in which a declaration is active File scope is also called global variable declared at the top of a source file declarations not placed in any functions can be used by any statements that are being executed in the system Function scope is also called local variable declared in a block { … } scope is within its block – lifetime while the block is executed

UniMAP SemI-09/10EKT120: Computer Programming26 Scope and Mechanics of Passing Values to Functions

UniMAP SemI-09/10EKT120: Computer Programming27

UniMAP SemI-09/10EKT120: Computer Programming28 Scope and Mechanics of Passing Values to Functions

UniMAP SemI-09/10EKT120: Computer Programming29 End Week 5 – Functions (1) Q & A!