Algorithms and Programming Functions
Lecture 28
Summary of Previous Lecture
while statement for statement break statement Nested loops
Summary of C program
execution steps
We are using Turbo C for
editing source code
Our Source code is passed to the compiler
which checks Errors and translate your source
code into machine code
Object Code is formed after
compilation, which is computer
understandable code!
Linker Links Object Code formed with
the other Library Files..
Library Files path settings which you already configured!
All the header files including stdio.h are
placed here!
After Linking, executable file is formed , Loader
loads it into memory for further
processes…
Today’s Topics Algorithms
FunctionsUsing functions in top-down design
Functions in C LanguageUser defined FunctionsParametersReturn values
Functions
A named sequence of instructions Also known as: modules, procedures,
subroutines, ... Give a name to a standard, frequently
used sequence of actions Specify ("call") that sequence by name
Function Definition
Define a function as:
<functionname>
{
<sequence>
}
Example: Inviting Saad to a party
Function DefinitionInviteToParty { dial 9876-5432 say "Hello Saad, it's " sayMyName() say "Would you like to come to my party on 10
July?" say "It's at 1 Ravi Road." say "Great! See you then. Bye Saad" hangUp() }
Function Parameters
Functions may have parameters They specify variations from call to call So that the same function can do
different things Depending on the value of the
parameters
Function Parameters …
For example: √4 = 2 √36 = 6
Both the above can be thought of as “calls” to the square root function
But one returns 2, the other returns 6 Depending on the value of the parameter
Function Definition
Define a function with parameters as:
<functionname> ( <parameter>,<parameter>, ... ) { <sequence> }
Example: Inviting someone to a party
Function Definition
inviteToParty ( person, date, place){ ringUp(person) askToParty(date, place) sayGoodbye(person, date) }
Example: Inviting someone to a partyFunction Definition
ringUp( person ){ set number to lookUpNumber(person) dial(number) say "hello," say person say "it's" sayMyName() }
Example: Inviting someone to a party
Function Definition
askToParty(date, location) { say "Would you like to come to my party
on" say date say "It's at" say location }
Example: Inviting someone to a party
Function Definition
sayGoodbye ( person, date ) { say "Great! See you then. Bye" say person hangUp() }
Top Down Design and Functions Bottom Up Design
Determine what simple sequences you will need to solve the problem
Code those sequences from primitives Build more complex sequences using the
simpler ones as "pseudo-primitives" Continue building increasingly complex
sequences Stop when you have a sequence which solves
the entire problem
Build simple functions first Then use them as building blocks for more
complex functions Example: Juggling
Top Down Design and Functions
Top-Down and Bottom-Up Design are really two sides of the same coin
Example: Getting a Degree - Top-DownYou don’t just walk in and pick up the piece of
paperYou do first year, second year, third year
(maybe fourth year), then hopefully you can get your degree!
Top Down Design and Functions
But how do you do first year?First semester, second semester
How do you do first semester?4 different subjects...
How do you do a subject? ...
Top Down Design and Functions
Getting a degree - Bottom-Up Do an interesting-looking subject Do another... Keep doing them until you have enough
for a degree...
Top Down Design and Functions
Obviously you need direction Bottom-up degree-getting strategies might
never see you with the right combination of subjects to actually graduate!
So elements of Top-down guidance are needed - what are we aiming at?
Top Down Design and Functions
Functions in C Language Topics
FunctionsParametersReturn values
printf() printf and scanf are functions, declared in
the file stdio.hThe preprocessor directive (#) directs the
compiler that the function which you are looking for is declared in the stdio.h file.
#include<stdio.h>
User-Defined Functions Create your own functions, similar to
printf() or scanf() Recall a procedure in an algorithm - a
named collection of instructionsInviteToPartyRingUpMakeToParty
A function implements the procedure or function parts of an algorithm.
Writing User-defined Functions Need to specify:
the name of the function its parameterswhat it returnsblock of statements to be carried out when the
function is called The block of statements is called the
“function body”
Prints a simple greeting.
procedure sayHello{ output “Hello World!”}
Main Program{
do procedure sayHello
}
Example: hello1.c
#include <stdio.h>
/* * Print a simple greeting. */
void sayHello ( void ){ printf(“Hello World!\n”);}
/* * Call a function which * prints a simple greeting. */
int main(void){ sayHello(); return 0;}
Prints a simple greeting.
procedure sayHello{ output “Hello World!”}
Main Program{
do procedure sayHello
}
Example: hello1.c
Example: hello1.c
Function definition
Function call
#include <stdio.h>
/* * Print a simple greeting. */
void sayHello ( void ){ printf(“Hello World!\n”);}
/* * Call a function which * prints a simple greeting. */
int main(void){ sayHello(); return 0;}
Example: hello1.c
Function name
Function body
#include <stdio.h>
/* * Print a simple greeting. */
void sayHello ( void ){ printf(“Hello World!\n”);}
/* * Call a function which * prints a simple greeting. */
int main(void){ sayHello(); return 0;}
Example: hello1.c
Return type
Formal Parameter List
#include <stdio.h>
/* * Print a simple greeting. */
void sayHello ( void ){ printf(“Hello World!\n”);}
/* * Call a function which * prints a simple greeting. */
int main(void){ sayHello(); return 0;}
Parameters Information passed to a function “Formal” parameters are local variables
declared in the function declaration. “Actual” parameters are values passed to
the function when it is called.
/* Print two numbers in order. */
void badSort ( int a, int b ){ int temp;
if ( a > b ) { printf("%d %d\n", b, a); } else { printf("%d %d\n", a, b); }}
Example: badsort.c
Parameters (aka Arguments)
Example: badsort.c
/* Print two numbers in order. */
void badSort ( int a, int b ){ int temp;
if ( a > b ) { printf("%d %d\n", b, a); } else { printf("%d %d\n", a, b); }}
int main(void){ int x = 3, y = 5;
badSort ( 10, 9 ); badSort ( y, x+4 ); return 0;}
Example: badsort.c
/* Print two numbers in order. */
void badSort ( int a, int b ){ int temp;
if ( a > b ) { printf("%d %d\n", b, a); } else { printf("%d %d\n", a, b); }}
Formal parameters
Actual parameters
Parameters (cont.) Parameters are passed by copying the
value of the actual parameters to the formal parameters.
Changes to formal parameters do not affect the value of the actual parameters.
int main(void){ int a = 3, b = 5;
printf("%d %d\n",a,b); badSwap ( a, b ); printf("%d %d\n",a,b);
return 0;}
Example: badswap.c
/* Swap the values of two variables. */
void badSwap ( int a, int b ){ int temp;
temp = a; a = b; b = temp;
printf("%d %d\n", a, b);}
Example: badswap.c
Output: 3 5
int main(void){ int a = 3, b = 5;
printf("%d %d\n",a,b); badSwap ( a, b ); printf("%d %d\n",a,b);
return 0;}
/* Swap the values of two variables. */
void badSwap ( int a, int b ){ int temp;
temp = a; a = b; b = temp;
printf("%d %d\n", a, b);}
Example: badswap.c
Output: 3 5
5 3
int main(void){ int a = 3, b = 5;
printf("%d %d\n",a,b); badSwap ( a, b ); printf("%d %d\n",a,b);
return 0;}
/* Swap the values of two variables. */
void badSwap ( int a, int b ){ int temp;
temp = a; a = b; b = temp;
printf("%d %d\n", a, b);}
Example: badswap.c
Output: 3 5
5 3
3 5
int main(void){ int a = 3, b = 5;
printf("%d %d\n",a,b); badSwap ( a, b ); printf("%d %d\n",a,b);
return 0;}
/* Swap the values of two variables. */
void badSwap ( int a, int b ){ int temp;
temp = a; a = b; b = temp;
printf("%d %d\n", a, b);}
Example: badswap.c
Calling function’s environment:
a: 3
b: 5
Called function’s environment:
a: 5
b: 3
int main(void){ int a = 3, b = 5;
printf("%d %d\n",a,b); badSwap ( a, b ); printf("%d %d\n",a,b);
return 0;}
/* Swap the values of two variables. */
void badSwap ( int a, int b ){ int temp;
temp = a; a = b; b = temp;
printf("%d %d\n", a, b);}
Parameters (cont.) If a function does not take parameters,
declare its formal argument list void.
void sayHello ( void ){ printf(“Hello World!\n”);}
sayHello();Function call:
Declaration:
Return Values Values are returned by copying a value
specified after the return keyword
/* Returns the larger of two numbers. */
int max (int a, int b){ int result;
if (a > b) { result = a; } else { result = b; }
return result;}
Example: max.c
Return type
/* Returns the larger of two numbers. */
int max (int a, int b){ int result;
if (a > b) { result = a; } else { result = b; }
return result;}
Example: max.c
For example:
The value of the expression
max(7,5)
is the integer 7.
/* Returns the larger of two numbers. */
int max (int a, int b){ int result;
if (a > b) { result = a; } else { result = b; }
return result;}
Example: max.c
This style okay.
Return Values (cont.) If a function does not return a value,
declare its return type void.
void sayHello ( void ){ printf(“Hello World!\n”);}
sayHello();Function call:
Declaration:
Summary We have studied,
What is a Function?How to write algorithm for a function?C Programming functions
Parameters Return types Function Call