Reverse words in a given string

Problem

https://practice.geeksforgeeks.org/problems/reverse-words-in-a-given-string/0

Solution

 

Key Pair
Problem :
 https://practice.geeksforgeeks.org/problems/key-pair/0
Solution

Count pairs with given sum

Problem :

http://practice.geeksforgeeks.org/problems/count-pairs-with-given-sum/0

Solution :

Matrix Transpose

Given a 2D array A, your task is to convert all rows to columns and columns to rows.
Input:
First line contains 2 space separated integers, N - total rows, M - total columns.
Each of the next N lines will contain M space separated integers.
Output:
Print M lines each containing N space separated integers.
Constraints:
$1\le N\le 10$
$1\le M\le 10$
$0\le A\left[i\right]\left[j\right]\le 100$ where $1\le i\le N$ and $1\le j\le M$

$\mathrm{Solution}$

Count frequency of each element in array

Write a program to count the frequency of each element in array , as example if we have 
int a[10]={5, 10, 2, 5, 50, 5, 10, 1, 2, 2};
the output should be 
number     frequency
5          3
10         2
2          3
50         1
1          1

Monk and Lucky Minimum

Problem
https://www.hackerearth.com/practice/data-structures/arrays/1-d/practice-problems/algorithm/monk-and-lucky-minimum-3/

Solution

Micro and Array Update

Problem 
https://www.hackerearth.com/practice/data-structures/arrays/1-d/practice-problems/algorithm/micro-and-array-update/

Solution

Maximum AND

Problem
https://www.hackerearth.com/practice/basic-programming/bit-manipulation/basics-of-bit-manipulation/practice-problems/algorithm/maximum-and/

Solution

Toggle bits given range

Problem 
http://practice.geeksforgeeks.org/problems/toggle-bits-given-range/0

Solution

Monk and his Friend

Problem 

https://www.hackerearth.com/practice/basic-programming/bit-manipulation/basics-of-bit-manipulation/practice-problems/algorithm/monk-and-his-friend/

Solution

Monk and the box of cookies

Problem

https://www.hackerearth.com/practice/basic-programming/bit-manipulation/basics-of-bit-manipulation/practice-problems/algorithm/monk-and-the-box-of-cookies/

Solution

The Great Kian

Problem
https://www.hackerearth.com/practice/basic-programming/implementation/basics-of-implementation/practice-problems/algorithm/the-great-kian/

Solution

Little Jhool and psychic powers

Problem

https://www.hackerearth.com/practice/basic-programming/implementation/basics-of-implementation/practice-problems/algorithm/psychic-powers/

Solution

Count Digits

Problem 

https://www.hackerearth.com/practice/basic-programming/implementation/basics-of-implementation/practice-problems/algorithm/count-digits-1/

Solution

C program to left rotate an array

Write a program to left rotate an array by n position

Example

Input

Input 10 elements in array: 1 2 3 4 5 6 7 8 9 10
Input number of times to rotate: 3

Output

Array after left rotation: 4 5 6 7 8 9 10 1 2 3
Solution

Count Set bits in an array of integers

assume you have an array of 5 integers and you want to count the numbers of set bits in all array elements , write a function to do that

Solution

Circular Bit Shift

Write two functions RL(data,n) which performs circular left shift on variable data by n bits , RR(data,n) which performs circular right shift on variable data by n bits
note: data is 1 byte variable

refer to this video to know more about circular bit shifts

Solution

Beautiful Matrix

Problem 
codeforces.com/problemset/problem/263/A

Solution

Teams Problem

Problem 
http://codeforces.com/contest/231/problem/A

Solution

What is dangling pointer

The following code snippet illustrate the idea of dangling pointers

Reverse Two Arrays Of The Same Size

write a C program to reverse two array elements of the same size 
as example if we have int a[]={1,2,3,4},int b[]={5,6,7,8}
after reversing we would have int a[]={5,6,7,8},int b[]={1,2,3,4}

Find the output of the following code

Output 

1    1    0    0

Explanation

Find the output of the following code

Answer

2147483647

Explanation

i is an uninitialized static variable so its default value is zero
also i automatically promoted to unsigned int (because we did not specify if its signed or unsigned)
then 0<=10 condition true 
inside while loop 0>2 false , i-- executed 
second iteration i becomes 2147483647 (int size on my machine is 4 bytes)
2147483647 <=10 false , while loop is bypassed and 2147483647 is printed.

Complicated Declaration

what does the following declaration mean 

void (*abc(int,void(*def)()))();

Answer & Explanation 

Find the output of the following code

Answer
i

Explanation 

char c=++*p++
this statement will be parsed as follow 
1)p++ p which is a char pointer is post incremented so p still points to 'h'
2)*p++ p is dereferenced to get value 'h'
3)++'h' is i

note:this result is highly compiler dependent , some compilers may fail to compile this code and others may get you this output

advise : never write a code which seems to be ambiguous and compiler dependent

Find the output of the following code

Output
20
C is sea

Explanation
in this question I introduce the concept of preprocessor operators 
concat(x,y) x##y this operator concatenate x and y 
string(a) #a #operator convert any macro constant into string
so after preprocessing this code you will have the following code

int myvar=20;
printf("%d\n",myvar);
printf("%s","C is sea");

Find the output of the following code

Output
lvalue required as increment operand

Explanation
after reading the code for the first time you may get tricked and say the output will be
c 
c++
python
java 
but this not the output , because you will get compiler error in line 6 when you try to modify the base address of an array which is already a constant pointer

Find the output of the following code

Output 
linker error (undefined symbol x)

Explanation 
extern keyword tells the compiler that the value of the variable x is not in this scope so the compiler does not know variable x memory location so he will not assign x memory location , otherwise during linking time if x is defined in another scope or file , its value will be printed

Find the output of the following code

Output

h h 
e e
l l
l l
o o

Explanation
message[i]=i[message]
because compilers convert message[i] into *(message+i)
where message is the array base address ,also i[message] is converted into
 *(i+message)
so the two expressions are the same

Big endian VS little endian

Write a C program to check if your processor is big endian or little endian 

solution

What is the output of the following C code

output 

4  2
6  2
2  0

Reverse bits of Byte

write a C function to reverse the bits of a Byte as example if we have variable unsigned char x=0x07=0b00000111 as input parameter after reversing its bits it would return 11100000

solution 

Palindrome String

Write a C code to check a String is palindrome or not , Some palindrome strings examples are "a", dad", "radar", "madam", "abcba" etc.

solution

From decimal to binary

Write a C program to convert an integer from decimal to binary , using logical bitwise operators

solution

what is the output

what is the output of this C code 
output:
66    B
4
Explanation:
union temp t={66,'A'};
this statement will initialize only the first member of the union x with 66 and the compiler will ignore the second value 'A', as one element is sufficient to initialize all union members as they share the same memory locations
sizeof(t) =4 size of largest element in memory location

what is the output of this C code

output :
compilation error in line 19 , as you can not assign two structures of different types
also there is a compilation error in line 21 as rational operators can not be applied on structures

compute occurrence of character in a string

write C Program print the frequency of a certain character in a string 

what is the output of this program

output
10 segmentation fault

explanation

find the output

what will be the output of the following code 


output will be 
8  8  8  4
size of a pointer to any data type is type independent , size of pointer depends on your machine address bus.
sizeof("clu")  here "clu" is treated as array of characters ={'c','l','u','\0'}
so sizeof("clu") is 4 bytes

palindrome number

Write A program to check if a positive integer is palindrome or not

Number of words in a string

Write a C function words(string) that accepts a string as input parameter and returns the number of words in this string 
as example
words("my name is mohamed") will return 4

What will be the output of the following program

the output is 
Egypt 
explanation 
string name is the base address of the string variable which is an array of characters

Even or Odd

Write a C program to check if any entered number is even or odd without the use of conditional statements (if,else)

No loops

Write a C program to print the numbers from 1 to 10 without using any looping statements (for/while/do while)
also do not write printf() 10 times

convert to uppercase

Write a function upper() that accepts a string and converts all its characters into uppercase characters 
as example upper("c programming")=C PROGRAMMING

reverse a string

Write a function reverse() that accepts a string and reverses it 

as example reverse("hello") would return "olleh"

string of numbers

write a function that accepts string of numbers and converts it to digits 
as example convert("123")=123

Remove all blank spaces in a string

Write a C program to remove all the blank spaces from a string.

as example if string is "hello world , C programming" then the output will be "helloworld,Cprogramming"

What will be the output of the following program

output

in this program we perform math operations on the base addresses of the functions , so the output is compiler dependant 
assume the base address of sub() is 4199876 and add() 4199856 and main() is 4199894
so the output will be 4199914

What will be the output of the following code 

Output
var1=0    var2=10    var3=1

Explanation 

Pointers and bitfields

what will be the output of the following code

the code creates compilation error , as you can not create a pointer to bit fields , simply because bit fields may not start at byte boundry

Swap structure values

Assume that you have a structure defined as follow 
struct two_integers {int n1;int n2;};
and this structure is initialized as follow
struct two_integers x={100,-100}; 
Write a C function that returns the same structure x but n1 and n2 are swapped

Structures

In the following code , assume that the base address of the structure is 2424384 (in decimal form) , what will be the output of the program 

Solution
2424384
2424384
2424388
2424392

Sorting 2D array

Assume you have 2D array of integers , int a[3][4]={8,7,6,5,
                                                                                                            -2,800,19,-40,
                                                                                                             1,-23,600,-500};

Write a C program to sort it in ascending order (from low to high)

Solution

Increment all array values using pointers

Write C function INC(int array[5],int n) that accepts two parameters array of five integers and integer, and adds the integer n to all array elements , then it returns the new array , as example if array[5]={1,5,7,0,2} and n =5 after function call we have  array[]={6,10,12,5,7}

Pointers and 2D arrays

Assume you have 2D array S[2][4]={{1234,56},
{1212,33},
{1434,80},
{1312,78}};
write a C program to print all the values and their corresponding addresses of this array
using pointers

Pointer Arithmetic

What will be the output of the following program 

2424388
2424392
2424428
2424416

size of double data type

Write a program to calculate the size of a double data type in terms of Bytes , Do not use the sizeof() operator

Solution

what will be the output of the following program

output will be garbage values
uninitialized array elements have garbage values

What will be the output of the following program

j=12
k=49

From C file to exe file

Describe in detail how a C program is compiled and executed 

Answer

1) The preprocessor code searches for preprocessor directives (mainly #include or #define) and substitute them with their codes,the output of this step creates an expanded file (.I file)

2) the compiler takes .I file and coverts the high level code into assembly then into machine language (binary format) and generate .obj file

3) the linker takes .obj file and link it with C standard library functions in your code 

and generates the executable version of your C code

what will be the output of the following program

x=4.5
y=14.8

What will be the output of the following program

output is
count=4
count=3
count=2
count=1
count=0

what is the output of the following program

output=110 
by default C functions return int values in case you did not specify the return type

what is the output of the following program

10
10
garbage value
if your function does not return any value , it must be declared as void