OOP344-Jason Quan C/C++ Programs & notes-20102

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pointer to functions

A pointer can be used to point to anything. Therefore you can also use it to point to a function, here’s an simple c program that uses pointer to function:

#include<stdio.h>
void windows(char,int);
void mac(char,int);
int main(void) {
  void (*platform)(char,int); /* this a declaration of a function pointer with 
a argument of char and int*/
  char name[30];
  int option;
  printf("Please enter your name: ");
  scanf("%s", &name);
  do{
  printf("Which platform 1.Windows, 2.Mac:");
  scanf("%d", &option);
  platform = (option < 2) ? windows : mac; /* this line assign where the 
platform pointer should point to.*/  
  (option > 2||option<1) && printf("error: pick 1 or 2\n"); /*Lazy Evaculation*/
  }while(option<1||option>2);
  platform(name , option);
  
  return 0;
}
void windows(char* str,int n) {
  printf("%s you've choosen option %d, you are a Windows user.\n",str,n);
}
void mac(char* str,int m) {
  printf(" %s you've chosen Option %d, you are Mac user.\n",str, m);
}

In this program two functions are declared: void Windows(char *str,int n) and void Mac(char *str ,int m) they both return void. But the output a line. Within the main() a void pointer call platform is declared with two arugments( char, int) which are values types that will be pasted to the corrsponding functions which is determine by this line : platform = (option < 2) ? windows : mac;

If the user chooses option 1 platform will be set to point to the windows function else Mac fun ction otherwise. To call the function, you would call it using the pointer platform by use a line: platform(name , option); this line will call the function.

decimal to binary with bitwise operators

here's a example of dec to binary using bitwise operator


#include <stdio.h>

void binary(int v, int mask){

for(mask;mask>0;mask = mask >>1){

printf(“%d”,!!(v & mask));  /*prints 1 or  0, since bitwise operator “&”  means: 1 & 1= 1 anything else =0.*/

}

}

int main(){

int a;

int m;

printf(“number:”);

scanf(“%d”,&a);

m=a>32? 1024:32;

binary(a,m);

printf(“\n”);

return 0;

}

the Mask: The length of the mask can be determine by an simple intger for example 30= 100000 64 =1000000 1024= 10000000000

The number: the number is an plain integer number. But when used with an bitwise operator it become a binary number such as: 1 & mask 1= 000001 mask= 100000 Therefore in the loop shifts the mask right 1 to determine if the position contains 1 or 0. If zero output prints zero else one.

set and unset bits

While I was studying for the OOP344 test, I created a small program that demonstrates how to set a bit or unset a bit. For example if the number is 1 and the binary is 000001. Therefore if I choose to set the bit 2 the binary will become 000011 and the number will become 3. However if I choose to unset 1 the binary will become 000010. Thus a set and unset bit function has been created.

#include <stdio.h>
#define mask 32
void printdata(int v, int m){
  for(m;m>0;m = m >>1){
    printf("%d",!!(v & m));
  }
printf("\n");
}

/*set bit to one or zero and output the binary*/
void set(int* v, int num){
  *v=((*v)^num); /*0^0=0 and 1^0=1* therefore the operator will set the  bit to 1 or 0*/ 
   printdata(*v,mask);
}

int main(){
int a;
int m;
do{
  printf(" enter number(number>32 to quit):\n");
  scanf("%d",&a);
if(a<32){
  printdata(a,mask);
  printf("the current number is: %d\n",a);
  printf("set bit:\n");
  scanf("%d",&m);
  set(&a,m);
  printf("The new number: %d\n", a);
  printf("unset bit:\n");
  scanf("%d",&m);
  set(&a,m);
  printf("The new Number: %d\n", a);
				}
   }while(a<32);
}