C++ Programming Code Examples
C++ > Strings Code Examples
Program to Implement String Matching Using Vectors
/* Program to Implement String Matching Using Vectors
This C++ program implements string matching using vectors. A text and a pattern is given as input. The pattern is searched for in the text and all instances of the pattern are given as output. */
#include<iostream>
#include<string.h>
#include<vector>
using namespace std;
void input_string(vector<char>& str)
{
char a;
while (1)
{
a = getchar();
if (a == '\n')
break;
str.push_back(a);
}
return;
}
void print_string(vector<char> strn)
{
for (std::vector<char>::iterator it = strn.begin();it != strn.end();++it)
{
cout<<*it;
}
return;
}
int match_string(vector<char>& original, vector<char> match)
{
vector<char>::iterator p,q, r;
int i = 0;
p = original. begin();
while (r <= match.end() && p <= original.end())
{
r = match.begin();
while (*p != *r && p < original.end())
{
p++;
i++;
}
q = p;
while (*p == *r && r <= match.end() && p<=original.end())
{
p++; i++;
r++;
}
if (r >= match.end())
{
original.erase(original.begin(), q + 1);
return (i - match.size() + 1);
}
if (p >= original.end())
return 0;
p = ++q;
}
}
int main()
{
std::vector<char> original,match;
int i,result,k=0,sum=0;
cout<<"Enter String:";
input_string(original);
cout<<"Enter Search Pattern:";
input_string(match);
if (match.size() > original.size())
{
cout<<"Error:Original string too small.";
}
do
{
result = match_string(original, match);
sum += result; //to store previous found position
if (result > 0)
{
k++;
cout<<"\nMatch found from Position = "<<sum;
}
} while (result > 0); //loop to find all patterns
if (k == 0)
cout<<"Error:Match Not Found";
return 0;
}
In while loop, condition is evaluated first and if it returns true then the statements inside while loop execute, this happens repeatedly until the condition returns false. When condition returns false, the control comes out of loop and jumps to the next statement in the program after while loop. The important point to note when using while loop is that we need to use increment or decrement statement inside while loop so that the loop variable gets changed on each iteration, and at some point condition returns false. This way we can end the execution of while loop otherwise the loop would execute indefinitely. A while loop that never stops is said to be the infinite while loop, when we give the condition in such a way so that it never returns false, then the loops becomes infinite and repeats itself indefinitely.
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program.
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In computer programming, loops are used to repeat a block of code. For example, when you are displaying number from 1 to 100 you may want set the value of a variable to 1 and display it 100 times, increasing its value by 1 on each loop iteration. When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop. A for loop is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.
Consider a situation, when we have two persons with the same name, jhon, in the same class. Whenever we need to differentiate them definitely we would have to use some additional information along with their name, like either the area, if they live in different area or their mother's or father's name, etc. Same situation can arise in your C++ applications. For example, you might be writing some code that has a function called xyz() and there is another library available which is also having same function xyz(). Now the compiler has no way of knowing which version of xyz() function you are referring to within your code.
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Get character from stdin. Returns the next character from the standard input (stdin). It is equivalent to calling getc with stdin as argument. The getchar() function is equivalent to a call to getc(stdin). It reads the next character from stdin which is usually the keyboard. getc() can read from any input stream, but getchar() reads from standard input. So getchar() is equivalent to getc(stdin). This function does not accept any parameter. On success, the character read is returned (promoted to an int value).
Logical Operators are used to compare and connect two or more expressions or variables, such that the value of the expression is completely dependent on the original expression or value or variable. We use logical operators to check whether an expression is true or false. If the expression is true, it returns 1 whereas if the expression is false, it returns 0. Assume variable A holds 1 and variable B holds 0:
Return iterator to beginning. Returns an iterator pointing to the first element in the vector. Notice that, unlike member vector::front, which returns a reference to the first element, this function returns a random access iterator pointing to it. If the container is empty, the returned iterator value shall not be dereferenced. The C++ function std::vector::begin() returns a random access iterator pointing to the first element of the vector. This function does not accept any parameter.
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Return iterator to end. Returns an iterator referring to the past-the-end element in the vector container. The past-the-end element is the theoretical element that would follow the last element in the vector. It does not point to any element, and thus shall not be dereferenced. Because the ranges used by functions of the standard library do not include the element pointed by their closing iterator, this function is often used in combination with vector::begin to specify a range including all the elements in the container. If the container is empty, this function returns the same as vector::begin. This function does not accept any parameter.
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Erase elements. Removes from the vector either a single element (position) or a range of elements ([first,last)). This effectively reduces the container size by the number of elements removed, which are destroyed. Because vectors use an array as their underlying storage, erasing elements in positions other than the vector end causes the container to relocate all the elements after the segment erased to their new positions. This is generally an inefficient operation compared to the one performed for the same operation by other kinds of sequence containers (such as list or forward_list).
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Return size. Returns the number of elements in the vector. This is the number of actual objects held in the vector, which is not necessarily equal to its storage capacity. vector::size() is a library function of "vector" header, it is used to get the size of a vector, it returns the total number of elements in the vector. The dynamic array can be created by using a vector in C++. One or more elements can be inserted into or removed from the vector at the run time that increases or decreases the size of the vector. The size or length of the vector can be counted using any loop or the built-in function named size(). This function does not accept any parameter.
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