Display String From Backward

#define _CRT_SECURE_NO_WARNINGS
#include "iostream"
#include "string.h"

using namespace std;
void menu(int &num)
{
	
	cout << "------------------- 
";
	cout << "1.String length 
";
	cout << "2.Stringbackward 
";
	cout << "3.Numb of words  
";
	cout << "4.String Concatenating 
";
	cout << "5.String Comparing (Incomplete) 
";
	cout << "6.Palindrome Checking(Incomplete) 
";
	cout << "7.Substring finding (Incomplete)
";
	cout << "8.Reserve String (Incomplete)
";
	cout << "9.Lowercase 
";
	cout << "10.Uppercase 
";
	cout << "--------------------- 
";
	cout << "What do u want ? 
";
	cin >> num;


}
void nhapxau( char a[100])
{
	cout << "Nhap xau A : ";
	cin.get(a,100);
	cout << "Xau vua nhap : ";
	cout << a;
	cout << "
";

}
void strlght(char a[100])
{
	int i = 0;
	i=strlen(a);
	cout << i;
	cout << "
";
}
void HoanVi(char &x, char &y)
{
	char temp = x;
	x = y;
	y = temp;
}
void strbw(char a[])
{
	for (int i = 0; i < strlen(a)/2; i++)
	{
		HoanVi(a[i], a[strlen(a) - 1 - i]);
	}
	cout << a << "
";
}
void count(char a[100])
{
	char p;
	int cnt=0;
	cout << "Look for ? ";
	cin >>p;
	for (int i = 0; i < strlen(a); i++)
	{
		if (a[i] == p)
		cnt++;
	}
	cout << "
";
	cout << "The Word '"<<p<<"' Show up " << cnt << " Times 
";

}
void lowercase(char *a)
{
	for (int i = 0; i<strlen(a); i++)
	if (a[i] >= 65 && a[i] <= 90)
		a[i] = a[i] + 32;
	puts(a);
}
void uppercase(char *a)
{
	for (int i = 0; i<strlen(a); i++)
		a[i] = toupper(a[i]); //if(a[i]>=97 && a[i]<=122)
	puts(a);						//a[i]=a[i]-32;

}

void concatenate(char *a)
{
	
	strcat(a, "-day la chuoi ky tu duoc them vao");
	puts(a);
}




void main()
{
	char a[100], b[100];
	int i,num;
	/////////////////////////////////////////////////////////
	nhapxau(a);
	menu(num);
	////////////////////////////////////////////////////////
	switch (num)
	{
	case 1: cout << "String length : 
"; strlght(a); break;
	case 2: cout << "Stringbackward : 
"; strbw(a);   break;
	case 3: cout << "Numb of words :  
"; count(a); break;
	case 4: cout << "Concatenating String 
"; concatenate(a); break;
	case 9: cout << "Lowercase : 
"; lowercase(a); break;
	case 10: cout << "Uppercase : 
"; uppercase(a); break;
	default: break;
	}
}