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==Array of function pointer==

<source lang="cpp">
#include <stdio.h>
int sum(int a, int b);
int subtract(int a, int b);
int mul(int a, int b);
int div(int a, int b);
int (*p[4]) (int x, int y);
int main(void)
{
int result;
int i, j, op;
p[0] = sum; /* address of sum() */
p[1] = subtract; /* address of subtract() */
p[2] = mul; /* address of mul() */
p[3] = div; /* address of div() */
printf("Enter two numbers: ");
scanf("%d %d", &i, &j);

printf("0: Add, 1: Subtract, 2: Multiply, 3: Divide\n");
do {
printf("Enter number of operation: ");
scanf("%d", &op);
} while(op<0 || op>3);
result = (*p[op]) (i, j);
printf("%d", result);
return 0;
}
int sum(int a, int b)
{
return a + b;
}
int subtract(int a, int b)
{
return a - b;
}
int mul(int a, int b)
{
return a * b;
}
int div(int a, int b)
{
if(b)
return a / b;
else
return 0;
}

</source>

==Arrays of Pointers to functions==

<source lang="cpp">
#include <stdio.h>
int sum(int, int);
int product(int, int);
int subtract(int, int);
int main()
{
int i = 0;
int a = 10;
int b = 5;
int result = 0;
int (*pfun[3])(int, int);
pfun[0] = sum;
pfun[1] = product;
pfun[2] = subtract;
for( i = 0 ; i < 3 ; i++)
{
result = pfun[i](a, b);
printf("\nresult = %d", result);
}
result = pfun[1](pfun[0](a, b), pfun[2](a, b));
printf("\n\nThe product of the sum and the subtract = %d\n",result);
}
int sum(int x, int y)
{
return x + y;
}
int product(int x, int y)
{
return x * y;
}
int subtract(int x, int y)
{
return x - y;
}

</source>

==Function pointer==

<source lang="cpp">
#include <stdio.h>
#include <string.h>
void check(char *a, char *b,int (*cmp)(const char *, const char *));
int main(void)
{
char s1[80]= "asdf", s2[80]="asdf";
int (*p)(const char *, const char *);
p = strcmp;

check(s1, s2, p);
return 0;
}
void check(char *a, char *b,int (*cmp)(const char *, const char *))
{
printf("Testing for equality.\n");
if(!(*cmp)(a, b)) {
printf("Equal");
}else {
printf("Not Equal");
}
}

</source>

==Function pointer 2==

<source lang="cpp">
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
int compvalues(const char *a, const char *b);
void check(char *a, char *b,int (*cmp)(const char *, const char *));
int main(void)
{
char s1[80]="123", s2[80]="123";
printf("Testing values for equality.\n");
check(s1, s2, compvalues);

return 0;
}
void check(char *a, char *b,int (*cmp)(const char *, const char *))
{
if(!(*cmp)(a, b))
printf("Equal");
else
printf("Not Equal");
}
int compvalues(const char *a, const char *b)
{
if(atoi(a)==atoi(b))
return 0;
else
return 1;
}

</source>

==Function pointer and use it call a function==

<source lang="cpp">
#include <stdio.h>
int sum(int a, int b);
int main(void)
{
int (*p) (int x, int y);
int result;
p = sum; /* get address of sum() */
result = (*p) (10, 20);
printf("%d", result);
return 0;
}
int sum(int a, int b)
{
return a+b;
}

</source>

==Function pointer: function call==

<source lang="cpp">

#include <stdio.h>
int *f(int x);
int count;
int main(void)
{
int *p;
p = f(110); /* return pointer */
printf("count (through p) is %d", *p);
return 0;
}
int *f(int x)
{
count = x;
return &count; /* return a pointer */
}

</source>

==Implementing arithmetic and array functions==

<source lang="cpp">
#include <stdio.h>

double add(double a, double b)
{
return a+b;
}
double subtract(double a, double b)
{
return a-b;
}
double multiply(double a, double b)
{
return a*b;
}
double array_op(double array[], int size, double (*pfun)(double,double))
{
double result = array[size-1];
int i = 0;
for(i = size-1 ; i>0 ; i--)
result = pfun(array[i-1], result);
return result;
}

int main()
{
double array[] = {11.0, 10.0, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.0, 1.0};
int i = 0;
int length = sizeof array/sizeof(double);
printf("The value of:\n");
for(i = 0 ; i< length ; i++)
{
printf("%.2f%s\n", array[i]);
}
printf(" is %.2lf\n", array_op(array,length,add));
printf("\nThe value of:\n");
for(i = 0 ; i< length ; i++)
{
printf("%.2lf%s\n", array[i]);
}
printf(" is %.2lf\n", array_op(array, length, subtract));
printf("\nThe value of:\n");
for(i = 0 ; i< length ; i++)
{
printf("%.2lf%s\n", array[i]);
}
printf(" is %.2lf\n", array_op(array, length, multiply));
}

</source>

==Initialize the function pointer array==

<source lang="cpp">
#include <stdio.h>
int sum(int a, int b);
int subtract(int a, int b);
int mul(int a, int b);
int div(int a, int b);
/* initialize the pointer array */
int (*p[4]) (int x, int y) = {
sum, subtract, mul, div
} ;
int main(void)
{
int result;
int i = 2, j = 2, op;

printf("0: Add, 1: Subtract, 2: Multiply, 3: Divide\n");
do {
printf("Enter number of operation: ");
scanf("%d", &op);
} while(op<0 || op>3);
result = (*p[op]) (i, j);
printf("%d", result);
return 0;
}
int sum(int a, int b)
{
return a + b;
}
int subtract(int a, int b)
{
return a - b;
}
int mul(int a, int b)
{
return a * b;
}
int div(int a, int b)
{
if(b)
return a / b;
else
return 0;
}

</source>

==Passing a Pointer to a function==

<source lang="cpp">
#include <stdio.h>
int sum(int,int);
int product(int,int);
int difference(int,int);
int any_function(int(*pfun)(int, int), int x, int y);
int main()
{
int a = 13;
int b = 51;
int result = 0;
int (*pf)(int, int) = sum;
result = any_function(pf, a, b);
printf("\nresult = %d", result );
result = any_function(product,a, b);
printf("\nresult = %d", result );
printf("\nresult = %d\n", any_function(difference, a, b));
}
int any_function(int(*pfun)(int, int), int x, int y){
return pfun(x, y);
}
int sum(int x, int y){
return x + y;
}
int product(int x, int y){
return x * y;
}
int difference(int x, int y){
return x - y;
}

</source>

==Pointing to functions==

<source lang="cpp">
#include <stdio.h>
int sum(int x, int y)
{
return x + y;
}
int product(int x, int y)
{
return x * y;
}

int main()
{
int a = 13;
int b = 5;
int result = 0;
int (*pfun)(int, int);
pfun = sum;
result = pfun(a, b);
printf("\npfun = sum result = %d", result);
pfun = product;
result = pfun(a, b);
printf("\npfun = product result = %d", result);
}

</source>

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