reverse function is out of scope in my cpp program

Question

#include <iostream>
#include <bits/stdc++.h>
#include <cstring>
using namespace std;

int LCS(string x, string y, int n, int m)
{
    int t[n + 1][m + 1];
    for (int i = 0; i <= n; i++)
        for (int j = 0; j <= m; j++)
        {
            if (i == 0 || j == 0)
                t[i][j] = 0;
        }
    for (int i = 1; i <= n; i++)
        for (int j = 1; j <= m; j++)
        {
            if (x[i - 1] == y[j - 1])
                t[i][j] = 1 + t[i - 1][j - 1];
            else
                t[i][j] = max(t[i - 1][j], t[i][j - 1]);
        }
    return t[n][m];
}

int main()
{
    string x;
    string y = reverse(x.begin(), x.end());
    cin >> x;
    cout >> LCS(x, y, x.length(), y.length());
    return 0;
}

op shows that the C:\Users\sagar\Videos\cpp_work\longest pallindromic subsequence LPA\main.cpp|29|error: conversion from 'void' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested|

anastaciu · Accepted Answer · 2020-07-01T11:24:22.577

You should ask for string before you reverse it, cin >> x; should be before you use std::reverse, because it's empty.

This line

cout>>LCS(x,y,x.length(),y.length());

has a typo, it should be cout << ....

std::reverse does not return the reversed string, it reverses it in place, you can't assign it to another std::string. This is the source of the error you show.

The string x will be reversed.

You may want something like:

string x;
string y;
cin >> x; //input x
y = x; //make a copy of x
reverse(y.begin(), y.end()); // reverse y
cout << LCS(x, y, x.length(), y.length());

Other notes:

The C++ standard does not allow for variable length arrays, int t[n + 1][m + 1]; is not valid C++, though some compilers allow its use.

using namespace std; is not recommended.

As is not #include <bits/stdc++.h>.

reverse function is out of scope in my cpp program

1 Answers1