why is a function-definition isn't allowed before "{"? - c++

Question

We we're tasked to write a program that
Display the inputted strings,
Count the number of characters in the string(s),
Count the number of vowels in the string(s),
Count the number of consonants in the string(s),
Convert the string(s) to uppercase,
Convert the string(s) to lowercase,
Compare the two strings and Combine the two strings
Now, I'm facing a problem where everytime I try to run a program it gets an error that says function-definition is not allowed here before { token and error expected } at end of input.
Code below:
#include <cstring>
#include <string>
#include <iostream>
#include <stdio.h>
using namespace std;
void Display_Inputted_Strings()
{
string str1,str2;
cin >> str1;
cin >> str2;
cout << str1 << endl;
cout << str2 << endl;
return;
}
void The_Number_Of_Character()
{
char str1[10];
cout << "Input you're First String: ";
cin >> str1;
char str2[10];
cout << "Input you're Second String: ";
cin >> str2;
cout << "Lenght of string 1: " << strlen(str1) << endl;
cout << "Lenght of string 2: " << strlen(str2) << endl;
}
void The_Number_Of_Vowels()
{
bool isVowel(char ch)
{
{
ch = toupper(ch);
return (ch=='A' || ch=='E' || ch=='I' ||
ch=='O' || ch=='U');
}
}
}
int countVowels(int str)
{
int isVowel;
int count = 0;
for (int i=0; i<str.length(); i++)
if (isVowel(str[i]))
++count;
return count;
int str;
cout << "Enter a string: ";
cin >> str;
cout << "There are " << countVowels(str) << " Vowels in this string" << endl;
return 0;
}
void The_Number_Of_Consonants()
{
bool isConsonant(char ch)
{
ch = toupper(ch);
return !(ch == 'A' || ch == 'E' ||
ch == 'I' || ch == 'O' ||
ch == 'U') && ch >= 65 && ch <= 90;
}
int totalConsonants(string str)
{
int count = 0;
for (int i = 0; i < str.length(); i++)
if (isConsonant(str[i]))
++count;
return count;
string str;
cout << "Enter a string: ";
cin >> str;
cout << "There are a total of " << totalConsonants(str) << " Consonant";
}
}
void Convert_Strings_To_Uppercase()
{
void convert(string & s1)
{
for(int i = 0; i<s1.length(); i++)
{
s1[i] = toupper(s1[i]);
}
}
{
string s1;
cout << "Enter a string: " << endl;
getline(cin, s1);
convert(s1);
cout << s1 << endl;
return 0;
}
}
void Convert_Strings_To_Lowercase()
{
void convert(string & s1)
{
for(int i = 0; i<s1.length(); i++)
{
s1[i] = tolower(s1[i]);
}
}
{
string s1;
cout << "Enter a string: " << endl;
getline(cin, s1);
convert(s1);
cout << s1 << endl;
return 0;
}
}
void Compare_Two_Strings()
{
{
char str1[10] = "String";
char str2[10] = "Strings";
int result;
result=strcmp(str1,str2);
if(result==0)
cout << "String are equal" << endl;
else
cout << "String are not equal" << endl;
return 0;
}
}
void Combine_Two_Strings()
{
{
string s1, s2, result;
cout << "Enter string s1: ";
getline(cin,s1);
cout << "Enter string s2: ";
getline(cin,s2);
result = s1+s2;
cout << result << endl;
return 0;
}
}
void Input_String()
{
string str1;
cout << "Input a String: ";
cin >> str1;
cout << "The String You Inputted: " << str1;
}
void Exit_Program()
{
cout << "Thank You.\n";
}
int main()
{
int str1,str2;
{
cout << "Input Two Strings: ";
getline(cin, str1);
getline(cin, str2)
}
int selected
do
{
std::cout << "A.(0) Display Inputted Strings\n";
std::cout << "B.(1) Count the number of characters in the string(s)\n";
std::cout << "C.(2) Count the number of vowels in the string(s)\n";
std::cout << "D.(3) Count the number of consonants in the string(s)\n";
std::cout << "E.(4) Convert the string(s) to uppercase\n";
std::cout << "F.(5) Convert the string(s) to lowercase\n";
std::cout << "G.(6) Compare the two strings\n";
std::cout << "H.(7) Combine the two strings\n";
std::cout << "I.(8) Input another\n";
std::cout << "J.(9) Exit Program\n";
std::cin >> selected;
switch (selected)
{
case 0:
Display_Inputted_Strings();
break;
case 1:
The_Number_Of_Character();
break;
case 2:
The_Number_Of_Vowels();
break;
case 3:
The_Number_Of_Consonants();
break;
case 4:
Convert_Strings_To_Uppercase();
break;
case 5:
Convert_Strings_To_Lowercase();
break;
case 6:
Compare_Two_Strings();
break;
case 7:
Combine_Two_Strings();
break;
case 8:
Input_String();
break;
case 9:
Exit_Program();
break;
default:
std::cout << "You have entered an invalid option\n";
}
} while (selected != 9);
}
}

Answer 1

You probably come to the world of C++ from the world of another language like Python. It is not allowed to define a nested function within another function in C++. However you may define a lambda that may have the same semantics. For example:
void Convert_Strings_To_Lowercase()
{
auto convert = [](string & s1)
{
for(int i = 0; i<s1.length(); i++)
{
s1[i] = tolower(s1[i]);
}
};
{
string s1;
cout << "Enter a string: " << endl;
getline(cin, s1);
convert(s1);
cout << s1 << endl;
}
}
P.S. I've just converted your function into something compilable, without checking whether the code has any meaning. For example, I removed the return 0; statement as your function has the void return type.