1. Week 6 – Functions (2)
PGT C Programming

2. Outline Recall - sample application functions that do not return value
functions that return a value
Recall – global variable vs. local variable
Passing parameters in functions :- Pass by value
Functions that return more than one value
Sample application-functions that return more than one value
Passing parameters in functions :- Pass by reference
Sample application
Recursive function
PGT C Programming

3. 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
Think!! Which function returns no value and which function returns a value.
What argument names do I want to feed in as parameters and what to return??

4. Sample application #include <stdio.h> void fnMenu();
float fnDeterminePrice(int);
float fnCalc(float,int);
void fnPrintResult(float);
int main()
{ int iCode,iQty;
float fPrice,fPay;
fnMenu();
printf("Enter item code and quantity: ");
scanf("%d %d", &iCode,&iQty);
fPrice = fnDeterminePrice(iCode);
fPay = fnCalc(fPrice,iQty);
fnPrintResult(fPay);
return 0; }
PGT C Programming

5. Enter item code and quantity: 1 3 Payment is 3.00
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"); }
float fnDeterminePrice(int iItemCode)
{ 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);
float fCalc(float fItemPrice, int iQuality)
{ float fTotal;
fTotal = fItemPrice*iQuantity;
return(fTotal);
void fnPrintResult(float fPayment)
{ printf("Payment is %.2f\n", fPayment);
Code Item Price
Papaya
Melon
Durian
Others
Enter item code and quantity: 1 3
Payment is 3.00
***************************
Enter item code and quantity: 9 3
Payment is 12.00

6. Global Variable vs. Local Variable
#include <stdio.h>
void fnMenu();
float fnDeterminePrice(int);
float fnCalc(float,int);
void fnPrintResult(float);
int iCode,iQty; float fPrice,fPay;
int main() {
fnmenu();
printf("Enter item code and quantity:");
scanf("%d %d", &iCode,&iQty);
fPrice= fnDeterminePrice(iCode);
fPay=fnCalc(fPrice,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");
modification
float fnDeterminePrice(int iCode) {
iCode--;
switch(iCode)
case 1:fPrice=1.00;break;
case 2:fPrice=2.00;break;
case 3:fPrice=3.00;break;
default:fPrice=4.00; }
return(fPrice);
float fnCalc(float fPrice,int iQuantity)
fPay=fPay+1;
fPay=fPrice*iQuantity;
return(fPay);
void fnPrintResult(float fPay)
{ printf("Payment is %.2f\n", fPay);
Output:
Code Item Price
Papaya
Melon
Durian
Others
Enter item code and quantity: 1 4
Payment is 16.00
Enter item code and quantity: 3 1
Payment is 2.00
However, sometimes we need to do some modifications from inside a function; using global variable will make things worse!!!
PGT C Programming

7. 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 manipulate the data stored in its own memory space
PGT C Programming

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

9. Functions that return more than one value
When we talk about functions that return more than one value it also means that we want to pass arguments by reference
passes addresses (references), NOT value or data
allows direct manipulation
changes will affect original data
PGT C Programming

10. Functions that return more than one value
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
PGT C Programming

11. 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
PGT C Programming

12. Sample application
Function that returns more than one value - arguments are passed by reference
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);
#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; }
Output
Enter marks for test1 and test2 : 70 80
Average marks are : 75.00
PGT C Programming

13. 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 address of the actual variable, NOT the value
During program execution to manipulate the data, the address stored will 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);
PGT C Programming

14. 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
PGT C Programming

15. Sample application
Write a C program that reads character and calculates numbers of vowel and consonant
Your program should have function:
fnRead – read character
fnFindCountVC – determine and calculate number of vowel or consonant
fnPrint - print number of vowel or consonant
PGT C Programming

16. Sample application #include <stdio.h> #include <string.h>
Enter character : f
Do you want to continue?y
Enter character : I
Enter character : k
Do you want to continue?n
Number of vowel : 1
Number of consonant : 2
#include <stdio.h>
#include <string.h>
char fnRead();
void fnFindCountVC(char, int*, int*);
void fnPrint(int,int);
int main()
{ char cCh, cChoice; int iCountV=0, iCountC=0; do
{ cCh = fnRead();
fnFindCountVC(cCh, &iCountV, &iCountC);
printf("Do you want to continue? ");
scanf("%c", &cChoice);
getchar();
}while((cChoice == 'y') ||(cChoice =='Y'));
fnPrint(iCountV,iCountC);
return 0; }
char fnRead()
{ char cCh1;
printf("Enter character : ");
scanf("%c", &cCh1);
return(cCh1);
void fnFindCountVC(char cCh1, int *iVowel, int *iConsonant) {
switch(cCh1)
{ case 'A':
case 'a':
case 'E':
case 'e':
case 'I':
case 'i':
case 'O':
case 'o':
case 'U':
case 'u': *iVowel = *iVowel +1;break;
default: *iConsonant = *iConsonant + 1; }
void fnPrint(int iVowel, int iConsonant)
printf("Number of vowel : %d\n", iVowel);
printf("Number of consonant : %d\n", iConsonant);
Functions that “return” more than one value i.e. arguments are passed by reference

17. Pass by Reference (Example)
#include <stdio.h>
void fnFun1(int, int*); //function prototype
int main(void) {
int iA=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(int iAA, int * iBB)//function definition
iAA++;
*iBB--;
printf("\n\nInside fun 1\n”);
printf(“iAA = %d iBB = %d”,iAA,iBB);
Output
Before fun 1
iA=5 iB = 10
Inside fun 1
iAA = 6 iBB = 9
After fun 1
iA = 5 iB = 9
PGT C Programming

18. 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 return statement
Eventually the base case gets solved and then that value works its way back up to solve the whole problem
Recursion is very useful in mathematical calculations and in sorting of lists
PGT C Programming

19. Recursive Functions Example: factorial Recursive relationship:
n! = n * ( n – 1 ) * ( n – 2 ) * … * 1
Recursive relationship:
( n! = n * ( n – 1 )! )
5! = 5 * 4!
4! = 4 * 3!…
Base case (1! = 0! = 1)
PGT C Programming

20. Recursive Functions(Example)
Factorial
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
PGT C Programming

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

22. Recursive Functions (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)
PGT C Programming

23. Recursive Functions (Example)
Diagram of Fibonacci function:
f( 3 )
f( 1 )
f( 2 )
f( 0 )
return 1
return 0
return +
PGT C Programming

24. 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 ); }
PGT C Programming

25. End Week 6 – Functions (2)
Q & A!
PGT C Programming