implement few functions of cstring library

#include <iostream>
#include <cstring>
using namespace std;
 
 
//Function to find string length
int strLen(char*);
 
 
//Copies the second string to the first and also returns the first string after copy
char* strCpy(char*, char*);
 
 
//Concatenates the strings. The first string will now have concatenated string. It will also return the same.
char* strCat(char*, char*);
 
 
 
int strLen(char* str)
{
  //for loop to find the lenght of a string. '\0' used for identifying end of the string.
  int i;
  for (i=0; str[i]!='\0'; i++);
  return i;
}
 
 
char* strCpy(char* dest, char* src)
{
  
  int i;
  for (i=0; src[i]!='\0'; i++)
      dest[i] = src[i];
  dest[i] = '\0';
  return dest;
}
 
char* strCat(char* dest, char* src)
{
  
  int len, i, j;
  len = strLen(dest);
  for (i=len, j=0; src[j]!='\0'; i++, j++)
      dest[i] = src[j];
  dest[i] = '\0'; 
  return dest; 
}
 
int main()
{
 
    
    char * str1;
    char * str2;
    
    char s1[20];
    char s2[20];
    
    str1 = s1;
    str2 = s2;
 
    cout << "Please enter your 1st string : ";
    cin >> s1;
    cout << "Please enter your 2nd string : ";
    cin >> s2;
    
    cout << "\nThe length of " << str1 << " is " << strLen(str1) << ".\n";
    cout << "The length of " << str2 << " is " << strLen(str2) << ".\n";
    str1 = strCat(str1, str2);
    cout << "\nString Concatenation Result : " << str1 << "\n";
    str1 = strCpy(str1, str2);
    cout << "String Copy Result : " << str1 << "\n\n";
    system("pause");
    return 0;
}