Most of the programs are meant to be compiled, run and to be explained for their behaviour. The puzzles/questions can be broadly put into the following categories:
I have used Gnu/Linux/gcc for all of them.
The order in which the programs appear doesn't have
any relation with the level of difficulty.
Please feel free to contact me if you need any help in solving the problems.
My contact info. is available here
And you might be interested in a few references for C programming,
which I personally found very interesting.
If you are preparing for campus interviews, you might find the following
link interesting:
http://placementsindia.blogspot.com
http://www.interviewmantra.net/category/interview-questions/c
Regards,
Gowri Kumar
#include<stdio.h>
#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))
int array[] = {23,34,12,17,204,99,16};
int main()
{
int d;
for(d=-1;d <= (TOTAL_ELEMENTS-2);d++)
printf("%d\n",array[d+1]);
return 0;
}
Find out what's going wrong.
#include<stdio.h>
void OS_Solaris_print()
{
printf("Solaris - Sun Microsystems\n");
}
void OS_Windows_print()
{
printf("Windows - Microsoft\n");
}
void OS_HP-UX_print()
{
printf("HP-UX - Hewlett Packard\n");
}
int main()
{
int num;
printf("Enter the number (1-3):\n");
scanf("%d",&num);
switch(num)
{
case 1:
OS_Solaris_print();
break;
case 2:
OS_Windows_print();
break;
case 3:
OS_HP-UX_print();
break;
default:
printf("Hmm! only 1-3 :-)\n");
break;
}
return 0;
}
hint
What's the expected output for the following program and why?
enum {false,true};
int main()
{
int i=1;
do
{
printf("%d\n",i);
i++;
if(i < 15)
continue;
}while(false);
return 0;
}
hintThe following program doesn't "seem" to print "hello-out". (Try executing it) #include <stdio.h> #include <unistd.h> int main()What could be the reason? |
#include <stdio.h> #define f(a,b) a##b #define g(a) #a #define h(a) g(a) int main()Just by looking at the program one "might" expect the output to be, the same for both the printf statements. But on running the program you get it as:
{
printf("%s\n",h(f(1,2)));
printf("%s\n",g(f(1,2)));
return 0;
}
#include<stdio.h> int main()If you expect the output of the above program to be NONE, I would request you to check it out!!
{
int a=10;
switch(a)
{
case '1':
printf("ONE\n");
break;
case '2':
printf("TWO\n");
break;
defa1ut:
printf("NONE\n");
}
return 0;
}
int main()Why does it happen so?
{
int* p;
p = (int*)malloc(sizeof(int));
*p = 10;
return 0;
}
| Input | Output |
| 0 | 0(0000000) |
| 5 | 2(0000101) |
| 7 | 3(0000111) |
int CountBits (unsigned int x )Find out the logic used in the above program.
{
static unsigned int mask[] = { 0x55555555,
0x33333333,
0x0F0F0F0F,
0x00FF00FF,
0x0000FFFF } ;
int i ;
int shift ; /* Number of positions to shift to right*/ for ( i =0, shift =1; i < 5; i ++, shift *= 2)
x = (x & mask[i ])+ ( ( x >> shift) & mask[i]);
return x;
}
#include <stdio.h>
int main()
{
float f=0.0f;
int i;
for(i=0;i<10;i++)
f = f + 0.1f;
if(f == 1.0f)
printf("f is 1.0 \n");
else
printf("f is NOT 1.0\n");
return 0;
}
#include <stdio.h>
int main()
{
int a = 1,2;
printf("a : %d\n",a);
return 0;
}
#include <stdio.h>
int main()
{
int i=43;
printf("%d\n",printf("%d",printf("%d",i)));
return 0;
}
void duff(register char *to, register char *from, register int count)Is the above valid C code? If so, what is it trying to acheive and why would anyone do something like the above?
{
register int n=(count+7)/8;
switch(count%8){
case 0: do{ *to++ = *from++;
case 7: *to++ = *from++;
case 6: *to++ = *from++;
case 5: *to++ = *from++;
case 4: *to++ = *from++;
case 3: *to++ = *from++;
case 2: *to++ = *from++;
case 1: *to++ = *from++;
}while( --n >0);
}
}
int CountBits(unsigned int x)
{
int count=0;
while(x)
{
count++;
x = x&(x-1);
}
return count;
}
int foobar(void);The following programs should be of some help in finding the answer: (Compile and run both the programs and see what happens)
int foobar();
#include <stdio.h> void foobar1(void)Program 2:
{
printf("In foobar1\n");
}
void foobar2()
{
printf("In foobar2\n");
}
int main()
{
char ch = 'a';
foobar1();
foobar2(33, ch);
return 0;
}
#include <stdio.h> void foobar1(void)
{
printf("In foobar1\n");
}
void foobar2()
{
printf("In foobar2\n");
}
int main()
{
char ch = 'a';
foobar1(33, ch);
foobar2();
return 0;
}
#include <stdio.h> int main()
{
float a = 12.5;
printf("%d\n", a);
printf("%d\n", *(int *)&a);
return 0;
}
int arr[80];File2.c
extern int *arr;
int main()
{
arr[1] = 100;
return 0;
}
#include<stdio.h> int main()
{
int a=1;
switch(a)
{ int b=20;
case 1: printf("b is %d\n",b);
break;
default:printf("b is %d\n",b);
break;
}
return 0;
}
#define SIZE 10 void size(int arr[SIZE])
{
printf("size of array is:%d\n",sizeof(arr));
}
int main()
{
int arr[SIZE];
size(arr);
return 0;
}
#include <stdlib.h> #include <stdio.h> void Error(char* s)
{
printf(s);
return;
}
int main()
{
int *p;
p = malloc(sizeof(int));
if(p == NULL)
{
Error("Could not allocate the memory\n");
Error("Quitting....\n");
exit(1);
}
else {
/*some stuff to use p*/ }
return 0;
}
#include <stdio.h> int main()
{
char c;
scanf("%c",&c);
printf("%c\n",c);
scanf(" %c",&c);
printf("%c\n",c);
return 0;
}
#include <stdio.h> int main()
{
char str[80];
printf("Enter the string:");
scanf("%s",str);
printf("You entered:%s\n",str);
return 0;
}
#include <stdio.h> int main()
{
int i;
i = 10;
printf("i : %d\n",i);
printf("sizeof(i++) is: %d\n",sizeof(i++));
printf("i : %d\n",i);
return 0;
}
#include <stdio.h>
void foo(const char **p) { }
int main(int argc, char **argv)
{
foo(argv);
return 0;
}
#include <stdio.h> int main()
{
int i;
i = 1,2,3;
printf("i:%d\n",i);
return 0;
}
#include <stdio.h> #include <stdlib.h> #define MAX 80 #define NUMBER '0' int getop(char[]);
void push(double);
double pop(void);
int main()
{
int type;
char s[MAX];
while((type = getop(s)) != EOF)
{
switch(type)
{
case NUMBER:
push(atof(s));
break;
case '+':
push(pop() + pop());
break;
case '*':
push(pop() * pop());
break;
case '-':
push(pop() - pop());
break;
case '/':
push(pop() / pop());
break;
/* ... * ... * ... */ }
}
}
#include<stdio.h>
#include<ctype.h>
char t[]={
0,0,0,0,0,0,12,18,33,63,
33,33,62,32,62,33,33,62,30,33,
32,32,33,30,62,33,33,33,33,62,
63,32,62,32,32,63,63,32,62,32,
32,32,30,33,32,39,33,30,33,33,
63,33,33,33,4,4,4,4,4,4,
1,1,1,1,33,30,33,34,60,36,
34,33,32,32,32,32,32,63,33,51,
45,33,33,33,33,49,41,37,35,33,
30,33,33,33,33,30,62,33,33,62,
32,32,30,33,33,37,34,29,62,33,
33,62,34,33,30,32,30,1,33,30,
31,4,4,4,4,4,33,33,33,33,
33,30,33,33,33,33,18,12,33,33,
33,45,51,33,33,18,12,12,18,33,
17,10,4,4,4,4,63,2,4,8,
16,63
};
int main(int argc,char** argv)
{
int r,pr;
for(r=0;r<6;++r)
{
char *p=argv[1];
while(pr&&*p)
{
int o=(toupper(*p++)-'A')*6+6+r;
o=(o<0||o>=sizeof(t))?0:o;
for(pr=5;pr>=-1;--pr)
{
printf("%c",( ( (pr>=0) && (t[o]&(1<<pr)))?'#':' '));
}
}
printf("\n");
}
return 0;
}
#include <stdio.h>
#include <stdlib.h>
#define SIZEOF(arr) (sizeof(arr)/sizeof(arr[0]))
#define PrintInt(expr) printf("%s:%d\n",#expr,(expr))
int main()
{
/* The powers of 10 */
int pot[] = {
0001,
0010,
0100,
1000
};
int i;
for(i=0;i<SIZEOF(pot);i++)
PrintInt(pot[i]);
return 0;
}
#include <stdio.h> int gcd(int u,int v)Also implement a C function similar to the above to find the GCD of 4 integers.
{
int t;
while(v > 0)
{
if(u > v)
{
t = u;
u = v;
v = t;
}
v = v-u;
}
return u;
}
int main()
{
int x,y;
printf("Enter x y to find their gcd:");
while(scanf("%d%d",&x, &y) != EOF)
{
if(x >0 && y>0)
printf("%d %d %d\n",x,y,gcd(x,y));
printf("Enter x y to find their gcd:");
}
printf("\n");
return 0;
}
#include <stdio.h>
#define PrintInt(expr) printf("%s : %d\n",#expr,(expr))
int main()
{
int y = 100;
int *p;
p = malloc(sizeof(int));
*p = 10;
y = y/*p; /*dividing y by *p */;
PrintInt(y);
return 0;
}
#include <stdio.h> int main()
{
int day,month,year;
printf("Enter the date (dd-mm-yyyy) format including -'s:");
scanf("%d-%d-%d",&day,&month,&year);
printf("The date you have entered is %d-%d-%d\n",day,month,year);
return 0;
}
#include <stdio.h> int main()
{
int n;
printf("Enter a number:\n");
scanf("%d\n",n);
printf("You entered %d \n",n);
return 0;
}
#include <stdio.h>
#define PrintInt(expr) printf("%s : %d\n",#expr,(expr))
int FiveTimes(int a)
{
int t;
t = a<<2 + a;
return t;
}
int main()
{
int a = 1, b = 2,c = 3;
PrintInt(FiveTimes(a));
PrintInt(FiveTimes(b));
PrintInt(FiveTimes(c));
return 0;
}
#include <stdio.h>
#define PrintInt(expr) printf("%s : %d\n",#expr,(expr))
int max(int x, int y)
{
(x > y) ? return x : return y;
}
int main()
{
int a = 10, b = 20;
PrintInt(a);
PrintInt(b);
PrintInt(max(a,b));
}
#include <stdio.h> int main()Well fixing the above code is straight-forward. To make the problem interesting, you have to fix the above code, by changing exactly one character. There are three known solutions. See if you can get all those three.
{
int i;
int n = 20;
for( i = 0; i < n; i-- )
printf("-");
return 0;
}
#include <stdio.h> int main()
{
int* ptr1,ptr2;
ptr1 = malloc(sizeof(int));
ptr2 = ptr1;
*ptr2 = 10;
return 0;
}
#include <stdio.h> int main()
{
int cnt = 5, a;
do {
a /= cnt;
} while (cnt --);
printf ("%d\n", a);
return 0;
}
#include <stdio.h> int main()
{
int i = 6;
if( ((++i < 7) && ( i++/6)) || (++i <= 9))
;
printf("%d\n",i);
return 0;
}
#include <stdlib.h> #include <stdio.h> #define SIZE 15 int main()
{
int *a, i;
a = malloc(SIZE*sizeof(int));
for (i=0; i<SIZE; i++)
*(a + i) = i * i;
for (i=0; i<SIZE; i++)
printf("%d\n", *a++);
free(a);
return 0;
}
#include <stdio.h> int main()
{
int a=3, b = 5;
printf(&a["Ya!Hello! how is this? %s\n"], &b["junk/super"]);
printf(&a["WHAT%c%c%c %c%c %c !\n"], 1["this"],
2["beauty"],0["tool"],0["is"],3["sensitive"],4["CCCCCC"]);
return 0;
}
#include <stdio.h> int main()
{
char dummy[80];
printf("Enter a string:\n");
scanf("%[^a]",dummy);
printf("%s\n",dummy);
return 0;
}
int a;b.c
int a = 10;main.c
extern int a;
int main()
{
printf("a = %d\n",a);
return 0;
}
Let's see what happens, when the files are compiled together:
bash$ gcc a.c b.c main.c bash$ ./a.out a = 10Hmm!! no compilation/linker error!!! Why is it so??
#define offsetof(a,b) ((int)(&(((a*)(0))->b)))
#define SWAP(a,b) ((a) ^= (b) ^= (a) ^= (b))What are the potential problems with the above macro?
#define DPRINTF(x) printf("%s:%d\n",#x,x)
int IAddOverFlow(int* result,int a,int b)So, how do you code the above function? (To put in a nutshell, what is the logic you use for overflow detection?)
{
/* ... */ }
#define ROUNDUP(x,n) ((x+n-1)&(~(n-1)))
#define isupper(c) (((c) >= 'A') && ((c) <= 'Z'))But there would be a serious problem with the above definition of macro, if it is used as follows (what is the problem??)
char c;But most of the libraries implement the isupper (declared in ctypes.h) as a macro (without any side effects). Find out how isupper() is implemented on your system.
/* ... */ if(isupper(c++))
{
/* ... */ }
int VarArguments(...)
{
/*....*/ return 0;
}
const char *p;
char* const p;
This work
by CH Gowri Kumar is licensed under a
Creative Commons Attribution-ShareAlike 3.0 Unported License.