Theory

Post-fix expressions have a very special place in computer science. Most of the computations are performed using stacks. In-fact a very simple calculator works on the principle of post-fix evaluation to get the answer. A post-fix notation is also known as the reverse Polish notation. The steps involved in evaluating a post-fix expression can be defined as follows. We use the concept of stacks to evaluate the same. ALGORITHM: Scan the post-fix string from left to right. Initialize an empty stack. Repeat the below steps 4 and 5 till all …

Stacks can be used to implement algorithms involving Infix, postfix and prefix expressions. So let us learn about them:- INFIX:- An infix expression is a single letter, or an operator, proceeded by one infix string and followed by another infix string. A A + B (A + B) + (C – D) PREFIX:- A prefix expression is a single letter, or an operator, followed by two prefix strings. Every prefix string longer than a single variable contains an operator, first operand and second operand A + A B + + …

A stack is a linear data structure that maintains the order in which elements are added. It only has one point to add and remove data.

From Wikipedia: A segmentation fault occurs when a program attempts to access a memory location that it is not allowed to access, or attempts to access a memory location in a way that is not allowed (for example, attempting to write to a read-only location, or to overwrite part of the operating system). Segmentation is one approach to memory management and protection in the operating system. It has been superseded by paging for most purposes, but much of the terminology of segmentation is still used, “segmentation fault” being an example. …

Question: What is the difference between doing:         ptr = (char **) malloc (MAXELEMS * sizeof(char *)); or:         ptr = (char **) calloc (MAXELEMS, sizeof(char*)); When is it a good idea to use calloc and when to use malloc ? There are two differences:- Firstly it is in the number of arguments, malloc() takes a single argument (memory required in bytes), while calloc() needs two arguments. Secondly, malloc() does not initialize the memory allocated, while calloc() initializes the allocated memory to ZERO. calloc() allocates a memory area, the length …

Question: In C, what is an unsigned char used for? How is this different from a regular char? In C, there are three distinct character types: char signed char unsigned char If you are using character types for text, use the unqualified char: it is the type of character literals like ‘a’ or ‘0’. it is the type that makes up C strings like “abcde” It also works out as a number value, but it is unspecified whether that value is treated as signed or unsigned. Beware character comparisons through …

Question: In C, what is the difference between using ++i and i++, and which should be used in the incrementation block of a for loop ? i++ is known as Post Increment whereas ++i is called Pre Increment. ++i will increment the value of i, and then return the incremented value. i++ will increment the value of i, but return the original value that i held before being incremented. For a for loop, either works. ++i seems more common, perhaps because that is what is used in Dennis Ritchie. In …

So if you supply n = 4 in the function what you get as the output is this. 0000 1000 0100 1100 0010 1010 0110 1110 0001 1001 0101 1101 0011 1011 0111 1111 You can download the code here.

Backtracking is the method of exhaustive search using divide and conquer. Sometimes the best algorithm for a problem is to try all the possibilities. This is always slow, but there are standard tools that can be used for help. Tools: algorithms for generating basic objects, such as binary strings [2n possibilities for n-bit string], permutations [n!], combinations [n!/r!(n-r)!], general strings [k-ary strings of length  n has kn possibilities], etc… Backtracking speeds the exhaustive search by pruning. Example Algorithms of Backtracking Binary Strings: generating all binary strings Generating k-ary Strings. The …

The tower of Hanoi is a mathematical puzzle. It consists of three rods, and a number of disks of different sizes which can slide onto any rod. The puzzle starts with the disks on one rod in ascending order of size, the smallest at the top, thus making a conical shape. The objective of the puzzle is to move the entire stack to another rod, satisfying the following rules:- Only one disk can be moved at a time. Each move consists of taking the upper disk from one of the …