trciky programs

#define just do the copy and not doing any evaluations:

• at first look it gives output like 1 but see carefully


example:



1)


#define square(x) x*x



int main()


{


  int x = 36/square(6); // Expended as 36/6*6


  printf("%d", x);


  return 0;


}

2)






#include <stdio.h>




#define MULTIPLY(a, b) a*b




int main()

{

    // The macro is expended as 2 + 3 * 3 + 5, not as 5*8

    printf("%d", MULTIPLY(2+3, 3+5));

    return 0;

}

// Output: 16







3)
root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# cat dptr.c 
#include<stdio.h>
int func(int **pointer_to_pointer);
int main()
{
 int a=10;
 int *ptr,**pptr;
 ptr = (int *) &a;
 pptr = &ptr;
 printf("\nvalue in *ptr =%d\n",*ptr);
 func(&ptr);
 printf("\nvalue in *ptr after func call =%d\n",*ptr);
 return 0;
}
int func(int **pointer_to_pointer) 
// to hold the address of another pointer
{
 printf("\nvalue in pointer_to_pointer =%d\n",**pointer_to_pointer);
 **pointer_to_pointer = 20;
}
root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# gcc dptr.c 
root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# ./a.out 

value in *ptr =10

value in pointer_to_pointer =10

value in *ptr after func call =20
root@selvakumar-Lenovo-B460e:/C_pgms/double_pointer# 

4)









root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# cat func1.c 


#include<stdio.h>

int add(int a,int b)
{
 return (a+b);
}

int main()
{
 //function pointer declaration
 int (*addptr)(int,int);
 //assinging address to function pointer
 addptr=&add;
 //calling via function pointer
 printf("\n%d\n",addptr(10,20));
 return 0;
}
root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# gcc func1.c 
root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# ./a.out 

30
root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# 
























root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# cat func2.c 
#include<stdio.h>
void function_a(void);
void function_b(void);
void main() {

     void (*fp)();

    fp = &function_a;

    (*fp)();  //prints "a"

    fp = &function_b;

    (*fp)();  //prints "b"

}

void function_a(void) {
      printf("a \n");
}

void function_b(void) {
     printf("b\n");
}

























root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# gcc func2.c 
root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# ./a.out 
a 
b
root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# 






















root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# cat calculator_using_fptr.c 
#include<stdio.h>
float Plus    (float a, float b) { return a+b; }
float Minus   (float a, float b) { return a-b; }
float Multiply(float a, float b) { return a*b; }
float Divide  (float a, float b) { return a/b; }

// Solution with a switch-statement -  specifies which operation to execute
void Switch(float a, float b, char opCode)
{
   float result;

   // execute operation
   switch(opCode)
   {
      case '+' : result = Plus     (a, b); break;
      case '-' : result = Minus    (a, b); break;
      case '*' : result = Multiply (a, b); break;
      case '/' : result = Divide   (a, b); break;
   }
   printf("\n result=%f",result);
}

// Solution with a function pointer
// a function which takes two floats and returns a float. The function pointer
// "specifies" which operation shall be executed.
void Switch_With_Function_Pointer(float a, float b, float (*pt2Func)(float, float))
{
   float result = pt2Func(a, b);    // call using function pointer
   printf("\n result=%f",result);
}

// Execute example code
int main()
{
   Switch(2, 5, /* '+' specifies function 'Plus' to be executed */ '+');
   Switch_With_Function_Pointer(2, 5, /* pointer to function 'Minus' */ &Minus);
   return 0;
}
root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# 

























root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# gcc calculator_using_fptr.c 
root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# ./a.out 

 result=7.000000
 result=-3.000000root@selvakumar-Lenovo-B460e:/C_pgms/function_pointer# 

root@selvakumar-Lenovo-B460e:/C_pgms/memory# cat last_byte.c 
#include<stdio.h>
/* program to mask last one byte of the given number*/
int main()
{
short a=0x0101; // two byte integer in hex format
short b;
printf("\n%d\n",a);
b = a & 0xff; // this mask last 1 byte
printf("\n%d\n",b);
return 0;
}
root@selvakumar-Lenovo-B460e:/C_pgms/memory# gcc last_byte.c 
root@selvakumar-Lenovo-B460e:/C_pgms/memory# ./a.out 

257

1
root@selvakumar-Lenovo-B460e:/C_pgms/memory# 

root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# cat void2.c 
#include<stdio.h>
 
struct Something
{
char *name;
int a;
};

int main()
{
 
int nValue =10;
float fValue =20.2;
char *name1 = "god";
char name2[] = "help";
struct Something sValue;
sValue.name="selva";
sValue.a=20;
 
void *pVoid;

//to showcase no error thrown
pVoid = &nValue; // valid
printf("nValue=%d\n",*((int *)pVoid));

pVoid = &fValue; // valid
printf("nValue=%f\n",*((float *)pVoid));

pVoid = name1; // note than not giving the address since its already pointer *name1
printf("name1=%s\n",((char *)(pVoid)));

pVoid = name2; // note than not giving the address since its already array name2[]
printf("name2=%s\n",((char *)(pVoid)));

pVoid = (sValue.name); // valid
printf("name=%s\n",((char *)(pVoid)));

pVoid = &(sValue); 
printf("struct something sValue->a =%d\n",(((struct Something *)(pVoid))->a));

return 0;
}
root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# gcc void2.c 
root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# ./a.out 
nValue=10
nValue=20.200001
name1=god
name2=help
name=selva
struct something sValue->a =20
root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# 

root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# cat voidptr.c 
#include<stdio.h> 
enum Type
{
    INT,
    FLOAT,
    STRING,
};

void Print(void *pValue, enum Type eType)
{
    int i;float f;char *c;
    switch (eType)
    {
        case INT:
     i = * ((int *)pValue);
     printf("\n%d\n",i);
            break;
        case FLOAT:
     f = *((float *)pValue);
     printf("\n%f\n",f);
            break;
        case STRING:
     c = (char *)pValue;
     printf("\n%s\n",c);
            break;
    }
}
 
int main()
{
    int nValue = 5;
    float fValue = 7.5;
    char *szValue = "Mollie";
 
    Print(&nValue, INT);
    Print(&fValue, FLOAT);
    Print(szValue, STRING); // note here no & symbol useed for char pointer
    return 0;
}
root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# gcc voidptr.c 
root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# ./a.out 

5

7.500000

Mollie
root@selvakumar-Lenovo-B460e:/C_pgms/voidptr# 

root@selvakumar-Lenovo-B460e:/C_pgms/sizeof# cat size.c 
#include<stdio.h>
/* */
int main()
{
printf("size of char * = %d\n",sizeof(char *));
printf("size of void * = %d\n",sizeof(void *));
return 0;
}
root@selvakumar-Lenovo-B460e:/C_pgms/sizeof# gcc size.c 
root@selvakumar-Lenovo-B460e:/C_pgms/sizeof# ./a.out 
size of char * = 4
size of void * = 4
root@selvakumar-Lenovo-B460e:/C_pgms/sizeof# 

#include <stdio.h>
#include <stdarg.h>

double average(int num,...)
{

    va_list valist;
    double sum = 0.0;
    int i;

    /* initialize valist for num number of arguments */
    va_start(valist, num);

    /* access all the arguments assigned to valist */
    for (i = 0; i < num; i++)
    {
       sum += va_arg(valist, int);
    }
    /* clean memory reserved for valist */
    va_end(valist);

    return sum/num;
}

int main()
{
   printf("Average of 2, 3, 4, 5 = %f\n", average(4, 2,3,4,5));
   printf("Average of 5, 10, 15 = %f\n", average(3, 5,10,15));
}