## C Q&A #6: An interesting difference between the C and C++ conditional operator

```int main (void)
{
int a = 5, b = 10, c;

c = a > 3 ? b = 5 : a = 3;
printf ("%d %d %d\n", a, b, c);
//cout << a << " " << b << " " << c << endl;

return 0;
}
```

Have a look at the above code, what will be the outcome if the code was in C language and if in C++ Language (replace with printf with cout)?

Directly going to the solution. Compilation error for C, and works perfect (no warnings) with C++. I saw this problem is a C question and answer book which didn’t bother to explain, so here is the explanation. Continue reading “C Q&A #6: An interesting difference between the C and C++ conditional operator”

## Find pairs of numbers in an array with difference ‘k’

The problem statement is, an long array is given with n elements, we need to find all the pairs of numbers in this long array which have a constant difference k. I will post three methods. The first method is the brute force method and has a runtime complexity O (n2), the next method has runtime complexity O (n*log (n)), and the last one will have the runtime complexity O (n).

## Jumble word solver again

I have already posted a jumbled word solver written in C language, although what I posted is actually become old, as I have changed some of the things in the code. I will update the post with this (hope to update!) with the new changes, but before it I would like to post the the same stuff in other languages and with different datastructure. Recently I am learning Perl and brushing up C++, therefore I will post jumble word solver written in C++ and Perl in this post.
Continue reading “Jumble word solver again”

## Check if a string is rotation of another

There are two strings. We need to find if one string is a rotation of the other. If yes then how many places it was rotated. The solution is pretty straightforward. I will describe two ways in this post. Continue reading “Check if a string is rotation of another”

## Implement queue using stack

The puzzle is to implement basic queue operations with using only basic stack operations. That is, a stack object is given, we need construct a wrapper for the queue functions, insert, remove, which will only use the stack object as its storage, and naturally will have to use the stack operations. I have already posted the opposite task in the post Implement stack using a queue

This can be done using two stack objects. We call these the first stack and the second stack. Although either the insert or the remove complexity will no more be O(1).

I have discussed the process gradually. I added the last solution when it clicked in my mind while reviewing this post.

## Plot histogram in terminal

We had assignments to print “*”s in different formation in undergraduate class, which I never liked as they were pointless. Now I got a somewhat justifiable application, plot histogram in terminal. In the last post Generating random numbers from Normal distribution in C I posted the C code to generate random numbers from the Normal distribution using the Polar method. In this post I am posting a simple code to plot the histogram of generated random numbers from this or any other distribution. Let me first post the code and then explain what is going on. Continue reading “Plot histogram in terminal”

## Generating random numbers from Normal distribution in C

I needed to write a random number generator in C which will generate random numbers from Normal Distribution (Gaussian Distribution). Without this component I couldn’t proceed to finish writing a C code for Heuristic Kalman Algorithm by Lyonnet and Toscano for some experiments. I selected the Marsaglia and Bray method also known as the Polar method to generate Normal random variables. Here is how it is done. Continue reading “Generating random numbers from Normal distribution in C”

## C LANGUAGE UERS! Y U NO SEE STANDARDS!

I had to make this. There are people who give a damn to the standards and follow the stone age Turbo C 3.1 compiler, run programs compiled by it. In the cases for compiler dependent and undefined behaviours, they try to guess in some way why the output was like that and get into a conclusion. Continue reading “C LANGUAGE UERS! Y U NO SEE STANDARDS!”

## C Q&A #5: A question about assignment operation and evaluation

Here is another C code snippet question. Consider the following piece of code, and spot if there is a problem in it or not.

```#include <stdio.h>

int main (void)
{
int x = 5;
+x += 1;
printf ("%d\n", +x);
return 0;
}
```

## Dynamically allocating 2d array with adjacent rows in memory

In a previous post “Allocating multidimentional array at runtime in C” I have explained a technique to allocate multidimensional arrays on runtime. While playing around with OpenMPI, I came to know that while sending/receiving a buffer, it requires the elements of a 2d matrix (or any dimension) to be in adjacent. Basically it does not care what you send, or receive, what it cares is the number of elements to be send should be adjacent to one another. In the previous post, the process will allocate the 2d or n-d matrix, but the rows of the matrix may not be adjacent to each other, as each row was allocated separately with malloc and then inserted into another array of pointers, each of which location points to the base addresses of these memory block. Read the post for details.

In C language the 2d array/matrix are stored in a row-major order, that is the elements of the matrix are stored adjacent to each other in the memory row wise. The first row comes first then just after the first row the second row starts, and so on. In the previous method the rows of the matrix may be scattered throughout the memory, as they are allocated with seperate malloc calls, but each of these returned addresses to the memory blocks (used as rows) are assigned to another array of pointers, which holds the rows together, and allows the mat[i][j] syntax to work.

For the applications in which, we might need to allocate the matrix dynamically at runtime, also have the rows of the matrix requires to be adjacent in the memory, and also make the mat[i][j] syntax work can be fulfilled by the following approach.