Answer to Question #157865 in C++ for M uzair shafiq

Question

Write a C++ program in which, read three c-string str, pat and rpat from user. Now your task is to find pat in str, replace pat with rpat in str if pat is found else display a message pat not found. Example 1 Example 2 Example 3 Example 4 Input: Str: abcdefabcdkuiyh Pat: abcd Rpat: xyz Output: After replace: Str: xyzefxyzkuiyh Input: Str: abcdefabcdkuiyh Pat: ab Rpat: xyz Output: After replace: Str: xyzcdefxyzcdkuiyh Input: Str: abcdefabcdkuiyh Pat: abc Rpat: xyz Output: After replace: Str: xyzdefxyzdkuiyh Input: Str: abcdefabcdkuiyh Pat: abcdefg Rpat: xyz Output: Pat not found Str: abcdefabcdkuiyh

Answer 1

#include <iostream>
#include <cstring>

#define MAXLENGTH 2555
using namespace std;

int main() {
    char *str = new char[MAXLENGTH];
    char *pat = new char[MAXLENGTH];
    char *rpat = new char[MAXLENGTH];

    //read all necessary data
    cout << "Input:" << endl << "Str:";
    cin.getline(str, MAXLENGTH);
    cout << "Pat:";
    cin.getline(pat, MAXLENGTH);
    cout << "Rpat:";
    cin.getline(rpat, MAXLENGTH);

    char *pch; //substring starting from pat
    bool checkPat = false; //check whether pat is in the string
    while (true) {
        pch = strstr(str, pat);
        if (pch == NULL) //if pat is not found
            break;
        else {
            //shift part of the string after pat occurrence
            char *leftover = pch + strlen(pat);
            char *copy = new char[MAXLENGTH];
            strncpy(copy, leftover, strlen(leftover));
            char *rightover = pch + strlen(rpat);
            strncpy(rightover, copy, strlen(leftover));
            //change pat to rpat
            strncpy(pch, rpat, strlen(rpat));
            //put null symbol to fix problem of c copy
            if (strlen(rpat) < strlen(pat))
                pch[strlen(pch) + strlen(pat) - strlen(rpat) - 2] = 0;
            checkPat = true;
        }
    }
    //Printing output
    cout << "Output:\n";
    if (checkPat)
        cout << "After replace:\nStr: " << str;
    else
        cout << "Pat not found\nStr: " << str;
    return 0;
}