使用递归 function 将小写转换为大写并执行 while

Question

#include<iostream>
using namespace std;


void recursiveToLower(char str[])
{
  do  {
    str[0] = toupper( str[0] ); 
    recursiveToLower( str+1 ); 
  }
  while ( str[0] != '\0' );
}

int main()
 {
 
  char str[];
 cin.get(str,80)
 cout<<str;
   recursivetoLower(str);
 
}

I have been trying to convert lower case to upper case using recursive function and do while loop as far as I know the syntax is fine but code is not working need help to compile it while compiling the code it is giving me some errors.

Answer 1

There is no use of the 'do while' loop if you want to use recursion. Either of them can be used to solve the problem. Also, there are few other errors as well, like you have not provided the size of the char array, which is required at the time of array declaration. And also you might have mistakenly called for the wrong function 'recursivetoLower(str)' though the actual function you have created is 'recursiveToLower(char str[])'. Remove the loop and insert a base condition and it should work. See the following code for reference.

void recursiveToLower(char str[])
{
    if(str[0] == '\0'){
        return;
    }
    str[0] = toupper( str[0] );
    recursiveToLower( str+1 );
}

int main(){
    char str[80];
    cin.get(str,80);
    cout<<str << endl;
    recursiveToLower(str);
    cout << str;
}

Answer 2

You either need iteration or recursion but not both!

Recursive:

void recursiveToLower(char str[])
{
 
   if(str[0] == '\0') return; //Base Case
    str[0] = tolower( str[0] ); 
    recursiveToLower( str+1 ); 
 
}

Iterative:

void iterativeToLower(char str[])
{
  do  {
    str[0] = tolower( str[0] ); 
    str += 1;
 }  while ( str[0] != '\0' );
}

Answer 3

You don't need to use a while loop. Just need to keep track of the state and call it recursively.

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

string recursive(string x, int i){
    if(i >= x.size()) return x;
    
    x[i] = toupper(x[i]);
    x = recursive(x, i+1);
    
    return x;
}

int main() {
    // your code goes here
    string x = "Convert to Upper";
    
    cout<<recursive(x, 0);
    return 0;
}

Answer 4

Let's see one by one the things that are wrong with your code. Here's the fixed code,

#include <iostream>
#include <cctype>
using namespace std;

void recursiveToLower(char str[])   
{
    if(str[0] != '\0')  //replaced while loop with simple if 
    {
        str[0] = tolower(str[0]);   //probably should be tolower as the function name suggests
        recursiveToLower(str + 1);
    }
    else 
    {
        return; //break condition for recursion
    }
}

int main()
{
    const unsigned SZ = 100;
    char str[SZ];   //In C++ array size cannot be dynamic , you did not specify array size
    cin >> str;
    recursiveToLower(str);
    cout << str <<endl;
}

Let's start with, loop and recursion don't go together for a task like this. This task could be done with loop or recursion, their combination which you have used don't make much sense, think about it.

Second, in C/C++, array size should be predefined.

I have added some helpful comments in the corrected code, if you are having problem in some part, you may ask in the comments.