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EKT120 COMPUTER PROGRAMMING

EKT120 COMPUTER PROGRAMMING . Functions (Part 2) Dr. Nik Adilah Hanin Bt. Zahri adilahhanin@unimap.edu.my. Recaps… Functions Prototype. #include < stdio.h > /* function prototype */ double product(double x, double y); int main() { double var1 = 3.0, var2 = 5.0; double ans ;

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EKT120 COMPUTER PROGRAMMING

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  1. EKT120COMPUTER PROGRAMMING Functions (Part 2) Dr. NikAdilahHanin Bt. Zahri adilahhanin@unimap.edu.my

  2. Recaps… Functions Prototype #include <stdio.h> /* function prototype */ double product(double x, double y); int main() { double var1 = 3.0, var2 = 5.0; double ans; /*function call*/ ans= product(var1, var2); printf("var1 = %.2lf\n" "var2 = %.2lf\n",var1,var2); printf("var1*var2 = %lf\n", ans); } /* function definition */ double product(double x, double y) { double result; result = x * y; return result; } Function prototype • Function prototype is a declaration; indicates the function exists • Should have function name, return type and parameter • Placed before main () • Tells compiler that the function will be defined later

  3. Recaps… Functions Call #include <stdio.h> /* function prototype */ double product(double x, double y); int main() { double var1 = 3.0, var2 = 5.0; double ans; /*function call*/ ans= product(var1, var2); printf("var1 = %.2lf\n" "var2 = %.2lf\n",var1,var2); printf("var1*var2 = %lf\n", ans); } /* function definition */ double product(double x, double y) { double result; result = x * y; return result; } • Consists of a function name followed by an argument expression list enclosed in parentheses • Function call hasthe following form: <function_name> (exp, exp ...) • main is the calling function • product is the called function

  4. Recaps… Functions Definition #include <stdio.h> /* function prototype */ double product(double x, double y); int main() { double var1 = 3.0, var2 = 5.0; double ans; /*function call*/ ans= product(var1, var2); printf("var1 = %.2lf\n" "var2 = %.2lf\n",var1,var2); printf("var1*var2 = %lf\n", ans); } /* function definition */ double product(double x, double y) { double result; result = x * y; return result; } • Function definition includes the body of a function • Function definition hasthe following form: <return_type> <function_name> (arg_typearg_name, ...) { … statements … }

  5. Recaps… Number, order and type of parameter • Number, order and type of parameters in the argument list of a function call and function definitionMUST match. int sum(int, int);//function prototype int sum(int num1, int num2) //function definition sum(x,y);//function call

  6. Recaps … Functions that RETURN a value //This program sums up two numbers #include <stdio.h> int sum(int,int); //function prototype int main(){ intx,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; } intsum(int num1, int num2){ //function definition int add; add = num1+num2; return add; }

  7. Recaps… Functions that DO NOT RETURN a value //This program sums up two numbers #include <stdio.h> void sum_print(int, int); //function prototype int main(){ intx,y; 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); }

  8. Recaps… Global and Local Variables //Compute Area & Perimeter of a circle #include <stdio.h> float pi = 3.14159;/* Global*/ int main() { float rad; /* Local */ printf( “Enter the radius “ ); scanf(“%f” , &rad); if ( rad > 0.0 ) { float area = pi * rad * rad; float peri = 2 * pi * rad; printf( “Area = %f\n” , area ); printf( “Peri = %f\n” , peri ); } else printf( “Negative radius\n”); printf( “Area = %f\n” , area ); return 0; } • Global variable • These variables are declared outside all functions, at the top of a source file. • Declarations not placed in any functions • Life time of a global variable is the entire execution period of the program. • Can be accessed by any function defined below the declaration

  9. Recaps… Global and Local Variables //Compute Area & Perimeter of a circle #include <stdio.h> float pi = 3.14159; /* Global */ int main() { float rad; /* Local */ printf( “Enter the radius “ ); scanf(“%f” , &rad); if ( rad > 0.0 ) { float area = pi * rad * rad; float peri = 2 * pi * rad; printf( “Area = %f\n” , area ); printf( “Peri = %f\n” , peri ); } else printf( “Negative radius\n”); printf( “Area = %f\n” , area ); return 0; } • Local variables • These variables are declared inside some functions (in a block { … }) • Life time is the entire execution period of the function in which it is defined. • Cannot be accessed by any other function  scope is within its block • In general variables declared inside a block are accessible only in that block.

  10. Today’s Outline • Passing parameters in functions :- Pass by value • Functions that return more than one value and its sample application • Passing parameters in functions :- Pass by reference and its application • Recursive function

  11. Sample Application • Write a C program that reads item code and quantity, then calculates the payment. Use functions: • fnMenu – print item code menu • fnDeterminePrice – determine price based on item code • fnCalc-calculate payment • fnPrintResult– print payment What argument names do I want to feed in as parameters and what to return?? Think!! Which function returns no value and which function returns a value.

  12. Sample Application: Local Variables #include <stdio.h> void fnMenu(); float fnDeterminePrice(int); float fnCalc(float,int); void fnPrintResult(float); int main() { intiCode,iQty; float fPriceUnit,fPay; fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fPriceUnit = fnDeterminePrice(iCode); fPay = fnCalc(fPriceUnit,iQty); fnPrintResult(fPay); return 0; }

  13. Sample Application: Local Variables #include <stdio.h> void fnMenu(); float fnDeterminePrice(int); float fnCalc(float,int); void fnPrintResult(float); int main() { intiCode,iQty; float fPriceUnit,fPay; fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fPriceUnit = fnDeterminePrice(iCode); fPay = fnCalc(fPriceUnit,iQty); fnPrintResult(fPay); return 0; } void fnMenu() { printf("Code\tItem\tPrice\n"); printf("1\tPapaya\t1.00\n"); printf("2\tMelon\t2.00\n"); printf("3\tDurian\t3.00\n"); printf("\tOthers\t4.00\n"); }

  14. Sample Application: Local Variables #include <stdio.h> void fnMenu(); float fnDeterminePrice(int); float fnCalc(float,int); void fnPrintResult(float); int main() { intiCode,iQty; float fPriceUnit,fPay; fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fPriceUnit = fnDeterminePrice(iCode); fPay = fnCalc(fPriceUnit,iQty); fnPrintResult(fPay); return 0; } void fnMenu() { printf("Code\tItem\tPrice\n"); printf("1\tPapaya\t1.00\n"); printf("2\tMelon\t2.00\n"); printf("3\tDurian\t3.00\n"); printf("\tOthers\t4.00\n"); } OUTPUT: Code Item Price 1 Papaya 1.00 2 Melon 2.00 3 Durian 3.00 Others 4.00

  15. Sample Application: Local Variables #include <stdio.h> void fnMenu(); float fnDeterminePrice(int); float fnCalc(float,int); void fnPrintResult(float); int main() { intiCode,iQty; float fPriceUnit,fPay; fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fPriceUnit = fnDeterminePrice(iCode); fPay = fnCalc(fPriceUnit,iQty); fnPrintResult(fPay); return 0; } OUTPUT: Code Item Price 1 Papaya 1.00 2 Melon 2.00 3 Durian 3.00 Others 4.00 Enter item code and quantity: 1 3

  16. Sample Application: Local Variables float fnDeterminePrice(intiItemCode) { float fPricing; switch(iItemCode) { case 1: fPricing = 1.00;break; case 2: fPricing = 2.00;break; case 3: fPricing = 3.00;break; default:fPricing = 4.00; } return fPricing; } #include <stdio.h> void fnMenu(); float fnDeterminePrice(int); float fnCalc(float,int); void fnPrintResult(float); int main() { intiCode,iQty; float fPriceUnit,fPay; fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fPriceUnit = fnDeterminePrice(iCode); fPay = fnCalc(fPriceUnit,iQty); fnPrintResult(fPay); return 0; }

  17. Sample Application: Local Variables #include <stdio.h> void fnMenu(); float fnDeterminePrice(int); float fnCalc(float,int); void fnPrintResult(float); int main() { intiCode,iQty; float fPriceUnit,fPay; fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fPriceUnit = fnDeterminePrice(iCode); fPay = fnCalc(fPriceUnit,iQty); fnPrintResult(fPay); return 0; } float fCalc(float fItemPrice, intiQuality) { float fTotal; fTotal = fItemPrice*iQuantity; return fTotal; }

  18. Sample Application Local Variables #include <stdio.h> void fnMenu(); float fnDeterminePrice(int); float fnCalc(float,int); void fnPrintResult(float); int main() { intiCode,iQty; float fPriceUnit,fPay; fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fPriceUnit = fnDeterminePrice(iCode); fPay = fnCalc(fPriceUnit,iQty); fnPrintResult(fPay); return 0; } void fnPrintResult(float fPayment) { printf("Payment is %.2f\n", fPayment); } OUTPUT: Code Item Price 1 Papaya 1.00 2 Melon 2.00 3 Durian 3.00 Others 4.00 Enter item code and quantity: 1 3 Payment is 3.00

  19. Sample Application: Global Variables void fnDeterminePrice() { switch(iCode) { case 1: fPriceUnit=1.00; break; case 2: fPriceUnit=2.00; break; case 3: fPriceUnit=3.00; break; default:fPriceUnit=4.00; } } #include <stdio.h> void fnMenu(); void fnDeterminePrice(); void fnCalc(); void fnPrintResult(); intiCode,iQty; float fPriceUnit,fPay; int main() { fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fnDeterminePrice(); fnCalc(); fnPrintResult(); return 0; }

  20. Sample Application: Global Variables #include <stdio.h> void fnMenu(); void fnDeterminePrice(); void fnCalc(); void fnPrintResult(); intiCode,iQty; float fPriceUnit,fPay; int main() { fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fnDeterminePrice(); fnCalc(); fnPrintResult(); return 0; } void fCalc() { fPay = fPriceUnit*iQty; }

  21. Sample Application: Global Variables #include <stdio.h> void fnMenu(); void fnDeterminePrice(); void fnCalc(); void fnPrintResult(); intiCode,iQty; float fPriceUnit,fPay; int main() { fnMenu(); printf("Enter item code and quantity:"); scanf("%d %d", &iCode,&iQty); fnDeterminePrice(); fnCalc(); fnPrintResult(); return 0; } void fnPrintResult() { printf("Payment is %.2f\n", fPay); } OUTPUT: Code Item Price 1 Papaya 1.00 2 Melon 2.00 3 Durian 3.00 Others 4.00 Enter item code and quantity: 1 3 Payment is 3.00

  22. Pass by Value • If a parameter is passed by value, then the value of the original data is copied into the function’s parameter (scope: local variable(s)) • In other words, it (i.e. local variable) has its own copy of the data • Changes to copy do not change original data • During program execution, it (i.e. local variable) will only manipulate the data stored in its own memory space

  23. Pass by Value (Example) #include <stdio.h> void fnFun1(int,int); //function prototype int main() { intiA=5, iB=10; printf("Before function1\n“); printf(" iA = %d iB = %d\n”, iA,iB); fnFun1(iA, iB); //function call printf("\nAfter function1\n“); printf(" iA = %d iB = %d\n”, iA,iB); return 0; } void fnFun1(intiAA,intiBB) //function definition { ++iAA; --iBB; printf("\n\nInside fnFun1\n)"; printf(“iAA = %d iBB = %d\n”, iAA,iBB); }

  24. OUTPUT Before fnFun 1 iA = 5 iB = 10 Inside fnFun 1 iAA = 6 iBB = 9 After fnFun 1 iA = 5 iB = 10 Pass by Value (Example) #include <stdio.h> void fnFun1(int,int); //function prototype int main() { intiA=5, iB=10; printf("Before fnFun1\n“); printf(" iA = %d iB = %d\n”, iA,iB); fnFun1(iA, iB); //function call printf("\nAfter fnFun1\n“); printf(" iA = %d iB = %d\n”, iA,iB); return 0; } void fnFun1(intiAA,intiBB) //function definition { ++iAA; --iBB; printf("\n\nInside fnFun1\n)"; printf(“iAA = %d iBB = %d\n”, iAA,iBB); }

  25. Functions that Return More than One Value • When we talk about functions that return more than one value it refers to passing arguments by reference • passes addresses (references), NOT value or data • allows direct manipulation • changes will affectoriginal data • There are cases where you need to manipulate the value of an external variable from inside a function, thus we pass the value by reference

  26. Pass by Reference • A function’s parameter that receives the location (memory address) of the corresponding actual variables • When we attach * (star) after the arg_type in the parameter list of a function, then the variable following that arg_type is passed by reference • It stores the addressof the actual variable, NOT the value • During program execution to manipulate the data, the address stored will have direct control to the memory space of the actual variable • Syntax: • In function protoype and function definition, put the * (star) after the data type Example : void fnReadMarks(float *,float *); • In function call, put the &(ampersand) before the argument name to be passed by reference Example : fnReadMarks(&fMarks1,&fMarks2);

  27. Pass by Reference • Pass by reference is useful in two situations: • when you want to return more than one value from a function • when the value of the actual parameter needs to be changed

  28. Pass by Reference (Example) #include <stdio.h> void fnFun1(int, int*); //function prototype int main(void) { intiA=5,iB=10; printf("Before fun 1\n”); printf(“iA = %d iB = %d”,iA,iB); fnFun1(iA, &iB); //function call printf(“\n\nAfter fun 1\n”); printf(“iA = %d iB = %d\n”,iA,iB); return 0; } void fnFun1(intiAA,int*iBB)//function definition { ++iAA; --*iBB; printf("\n\nInside fnFun1\n”); printf(“iAA = %d iBB = %d”,iAA,*iBB); }

  29. OUTPUT Output Before fnFun1 iA=5 iB = 10 Inside fnFun1 iAA = 6 iBB = 9 After fnFun1 iA = 5 iB = 9 Pass by Reference (Example) #include <stdio.h> void fnFun1(int, int*); //function prototype int main(void) { intiA=5,iB=10; printf("Before fun 1\n”); printf(“iA = %d iB = %d”,iA,iB); fnFun1(iA, &iB); //function call printf(“\n\nAfter fun 1\n”); printf(“iA = %d iB = %d\n”,iA,iB); return 0; } void fnFun1(intiAA,int*iBB)//function definition { ++iAA; --*iBB; printf("\n\nInside fnFun1\n”); printf(“iAA = %d iBB = %d”,iAA,*iBB); }

  30. Sample Application • Write a C program that calculates and prints average of 2 test marks. • Your program should have functions: • fnReadMarks – read 2 test marks • fnCalcAvg – calculate average of two test marks • fnPrint - print average

  31. #include <stdio.h> void fnReadMarks(float*,float*); float fnCalcAvg(float,float); void fnPrint(float); int main(void) { float fMarks1, fMarks2, fAvg; fnReadMarks(&fMarks1,&fMarks2); fAvg = fnCalcAvg(fMarks1,fMarks2); fnPrint(fAvg); return 0; } void fnReadMarks(float *fM1,float *fM2) { printf("Enter marks for test1 and test2 : "); scanf("%f %f", fM1,fM2); //notice no & } float fnCalcAvg(float fM1, float fM2) { return((fM1 + fM2)/2); } void fnPrint(float fAverage) { printf("\nAverage marks are :%.2f\n",fAverage); } Sample Application Function that returns more than one value - arguments are passed by reference

  32. #include <stdio.h> void fnReadMarks(float*,float*); float fnCalcAvg(float,float); void fnPrint(float); int main(void) { float fMarks1, fMarks2, fAvg; fnReadMarks(&fMarks1,&fMarks2); fAvg = fnCalcAvg(fMarks1,fMarks2); fnPrint(fAvg); return 0; } void fnReadMarks(float *fM1,float *fM2) { printf("Enter marks for test1 and test2 : "); scanf("%f %f", fM1,fM2); //notice no & } float fnCalcAvg(float fM1, float fM2) { return((fM1 + fM2)/2); } void fnPrint(float fAverage) { printf("\nAverage marks are :%.2f\n",fAverage); } Sample Application Function that returns more than one value - arguments are passed by reference Enter marks for test1 and test2 : 70 80 Average marks are : 75.00

  33. Recursive Functions • Recursion is a term describing functions which are called by themselves (functions that call themselves) • Recursive function has two parts i.e.base case and not base case • If not base case, the function breaks the problem into a slightly smaller, slightly simpler, problem that resembles the original problem and • Launches a new copy of itself to work on the smaller problem, slowly converging towards the base case • Makes a call to itself inside the returnstatement • Eventually the base case gets solved and then that value works its way back up to solve the whole problem • Useful in mathematical calculations and in sorting of lists

  34. Recursive Functions: Factorial • Example: factorial n! = n * ( n – 1 ) * ( n – 2 ) * … * 1 • Recursive relationship: ( n! = n * ( n – 1 )! ) • Example: 4! 4! = 4 * 3! 3! = 3 * 2! 2!=2*1! 1!=1*0! • Base case (1! = 0! = 1)

  35. Recursive Functions: Factorial • Factorial of 4 4 * 6 = 24 is returned Factorial(4) 3 * 2 = 6 is returned 4 * Factorial(3) 3 * Factorial(2) 2 * 1 = 2 is returned 2 * Factorial(1) Value 1 is returned 1

  36. Recursive Functions: Factorial • #include <stdio.h> • intfnFactorial(int); • void main() • { • intiN=4; • printf(“Factorial %d is %d“,n, fnFactorial(n)); • } • intfnFactorial(intiN) • { • if(iN <= 1) //base case • return 1; • else • return ( iN * fnFactorial(iN-1)); • } • Call function name itself

  37. Recursive Functions(Fibonacci Series) • Example : Fibonacci series 0, 1, 1, 2, 3, 5, 8... • Each number is the sum of two previous numbers • Example of a recursive formula: fib(n) = fib(n-1) + fib(n-2) Fibonacci series of 3: fib(3) = fib(2) + fib(1) fib(2) = fib(1) + fib(0) fib(1) = 1 fib(0) = 0

  38. f( 3 ) return f( 2 ) + f( 1 ) return f( 1 ) f( 0 ) return 1 + return 1 return 0 Recursive Functions(Example) • Diagram of Fibonacci function: = 2 = 1 = 1

  39. Recursive Functions(Example) • Sample code for fibonacci function long fnFibonacci( long lN ) { if ( lN == 0 || lN == 1 ) //base case return lN; else return fnFibonacci(lN–1)+ fnFibonacci(lN–2); }

  40. End Functions (2) Q & A!

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