Af Functions [21_01]

8/8/2019 Af Functions [21_01]

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21-01-03 P.P.Chakrabarti, IIT Kharagpur1

Functions

P. P. Chakrabarti

8/8/2019 Af Functions [21_01]



Query onswitch:

int main(){ char choice;

switch (choice = getchar()) {

case ‘r’ :case ‘R’: printf(“Red\n”);break;

case ‘b’ : printf(“small b\n”);case ‘B’ : printf(“Blue\n”);

break;case ‘g’ :case ‘G’: printf(“Green\n”);

break;default: printf(“Black\n”);

}}

[ppchak]$ ./a.outR

Red[ppchak]$ ./a.outBBlue[ppchak]$ ./a.out

rRed[ppchak]$ ./a.outbsmall b

Blue[ppchak]$ ./a.outkBlack

8/8/2019 Af Functions [21_01]



Library functions

#include<math.h>int main()

{ float x,y,z;scanf(“%f”, &x);printf(“tan(asine(%f/2) = %f \n”, x, tan(asine(x/2.0)));scanf(“%f%f%f”, &x,&y,&z);printf(“pow(%f, pow(%f, pow(%f, 1.0/3.0))) = %f\n”,

x,y,z, pow(x, pow(y, pow (z, 1.0/3.0))));}

How many of them arehere?

compile with –lm option

8/8/2019 Af Functions [21_01]



User defined functions: Ex 1

main(){ float cent, fahr;

scanf(“%f”,&cent);fahr = cent2fahr(cent);printf(“%fC = %fF\n”,

cent, fahr);}

float cent2fahr(float data){

float result;result = data*9/5 + 32;return result;

}

8/8/2019 Af Functions [21_01]



How it runs:float cent2fahr(float data){

float result;

printf(“data = %f\n”, data);result = data*9/5 + 32;return result;printf(“result = %f\n”, result);

}main(){ float cent, fahr;

scanf(“%f”,&cent);printf(“Input is %f\n”, cent);fahr = cent2fahr(cent);printf(“%fC = %fF\n”, cent, fahr);

}

[ppchak]$ gcc test20.c[ppchak]$ ./a.out32

Input is 32.000000data = 32.00000032.000000C = 89.599998F[ppchak]$./a.out-45.6Input is -45.599998data = -45.599998-45.599998C = -50.079998F[ppchak]$

8/8/2019 Af Functions [21_01]



Function Control Flow /* print banner line */ void print_banner (){

printf(“**************\n”);}

int main (){

. . .print_banner ();. . .print_banner ();

}

main (){

print_banner ();

print_banner ();

}

print_banner {

}

print_banner {

}

8/8/2019 Af Functions [21_01]



Function Type and Value? A function can return a value.? Like all values in C, a function return value has a type.?

The function has the type of its returned value.

/* Get number from user */ int get_input (void){

int num;printf (“Enter a number:”);scanf (“%d”, &num);return (num );

}

function type

return statement

returned value

8/8/2019 Af Functions [21_01]



Calling a function

? A value-returning function is called byincluding it in an expression.

int main (){

int x, y;x = get_input() ;y = get_input() ;printf (“ %d + %d = %d\n”,

x, y, x+y);}

Note : A value returningfunction can be usedanywhere an expression of the same type can be used.

8/8/2019 Af Functions [21_01]



return

? In a value-returning function (result type is not void)return does two distinct things :

?

1. specify the value returned by the execution of thefunction? 2. terminate that execution of the function.

? In a void function:?

return is optional at the end of the function body.? return may also be used to terminate execution of the

function explicitly.? No return value should appear following return.

8/8/2019 Af Functions [21_01]



void compute_and_print_itax (){

double income;scanf (“%f”, &income);if (income < 50000) {

printf (“Income tax = Nil\n”);return;

}if (income < 60000) {

printf (“Income tax = %f\n”, 0.1*(income-50000));return ;

}

if (income < 150000) {printf (“Income tax = %f\n”, 0.2*(income-60000)+1000);return ;

}printf (“Income tax = %f\n”, 0.3*(income-150000)+19000);

}

Terminate functionexecution beforereaching the end

8/8/2019 Af Functions [21_01]



Function parameters? It is very often useful if a function can operate

on different data values each time it is called.Such values are function (input) parameters.

? The function specifies its inputs as parametersin the function declaration.

/* Find area of a circle with radius r */ double area ( double r ){

return (3.14159*r*r) ;}

parameter

8/8/2019 Af Functions [21_01]



Arguments? The function call must include a matching

argument for each parameter.?

When the function is executed, the value of theargument is substituted for the parameter.

int main (void){ . . .

double circum;. . .area1 = area (circum/2.0 );. . .

}

double area ( double r ){

return (3.14*r*r);}

parameter passing

8/8/2019 Af Functions [21_01]



Another Example

main(){

int numb, flag, j=3;scanf(“%d”,&numb);while (j <=numb)

{flag = prime(j);

if (flag==0) printf(“%d isprime\n”,j); j++;}

}

int prime(int x){

int i, test;i=2, test =0;while ((i <= sqrt(x)) && (test==0))

{ if (x%i==0) test = 1;

i++;}return test;

}

8/8/2019 Af Functions [21_01]



Tracking the flow of controlmain(){

int numb, flag, j=3;scanf(“%d”,&numb);printf(“numb = %d \n”,numb);while (j <=numb){ printf(“Main, j = %d\n”,j);

flag = prime(j);printf(“Main, flag = %d\n”,flag);

if (flag==0) printf(“%d isprime\n”,j);

j++;}

}

int prime(int x){

int i, test;

i=2, test =0;printf(“In function, x = %d \n”,x);while ((i <= sqrt(x)) && (test ==0)){ if (x%i==0) test = 1;

i++;

}printf(“Returning, test = %d \n”,test);return test;

}

8/8/2019 Af Functions [21_01]



The run

[ppchak]$ gcc -lm test22.c[ppchak]$ ./a.out5numb = 5Main, j = 3In function, x = 3Returning, test = 0

Main, flag = 03 is primeMain, j = 4In function, x = 4

Returning, test = 1Main, flag = 1Main, j = 5In function, x = 5Returning, test = 0Main, flag = 05 is prime[ppchak]$

Af Functions [21_01]

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