DSA string operation

#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;

int i, j, k;

int str_len(char str[])
{
int length = 0;
for(i=0; str[i]!='\0'; i++)
length++;
return length;
}

void str_cpy(char str[])
{
int l = str_len(str);
char str_cp[l];
for(i=0; i<l; i++)
str_cp[i] = str[i];
    str_cp[l] = '\0';
cout<<"Copied string is "<<str_cp<<endl;
}

void str_cmp(char str1[], char str2[])
{
int count = 0, l1 = str_len(str1), l2 = str_len(str2);
if(l1 == l2)
{
for(i=0; i<l1; i++)
{
if(str1[i] == str2[i])
count++;
}
if(count == l1)
cout<<"Both strings are same";
else
cout<<"Both strings are not same";
}
else
{
cout<<"Both strings are not same";
return;
}
}

void str_cat(char str1[], char str2[])
{
j=0;
for(i=str_len(str1); str2[j]!='\0'; i++)
str1[i] = str2[j++];
str1[i] = '\0';
cout<<"Concatenation of strings is: "<<str1;
}

void str_rev(char str[])
{
int l = str_len(str), j=0;
char rev[l];
for(i=l-1; i>=0; i--)
rev[j++] = str[i];
rev[j] = '\0';
cout<<"Reverse of the string is: "<<rev;
}

void str_palin(char str[])
{
    int l = str_len(str);
char pal[l];
int j=0,count=0;
for(i=l-1; i>=0; i--)
  pal[j++] = str[i];
pal[j] = '\0';
for(i=0; i<l; i++)
{
  if(str[i] == pal[i])
count++;
  else
break;
}
(count == l)?cout<<"String is palindrome":cout<<"String is not a palindrome";
}

void sub_str(char str[], char sub[])
{
    j = 0;
for(i=0; str[i]; i++)
if(str[i] == sub[j])
for(k=i, j=0; str[k] && sub[j]; j++, k++)
if(str[k]!=sub[j])
break;
if(!sub[j])
{
cout<<"Substring";
return;
}
cout<<"Not a substring";
return;
}

int main()
{
char str1[100], str2[100];
int ch;
while(1)
{
cout<<"\n\n**********String Operations**********";
cout<<"\n\n1. Length of string";
cout<<"\n2. Copy the string";
cout<<"\n3. Compare the two strings";
cout<<"\n4. Concatenation of two strings";
cout<<"\n5. Reverse the string";
cout<<"\n6. Check if the string is palindrome or not";
cout<<"\n7. Check if one string is substring of another string or not";
cout<<"\n8. Exit";
cout<<"\nEnter your choice: ";
cin>>ch;
switch(ch)
{
case 1: cin.getline(str1, 100);
cout<<"\nEnter string: ";
cin.getline(str1, 100);
cout<<"Length of the string is "<<str_len(str1);
break;
case 2: cin.getline(str1, 100);
cout<<"\nEnter string: ";
cin.getline(str1, 100);
str_cpy(str1);
break;
case 3: cin.getline(str1, 100);
cout<<"\nEnter first string: ";
cin.getline(str1, 100);
cout<<"Enter second string: ";
cin.getline(str2,100);
str_cmp(str1, str2);
break;
case 4: cin.getline(str1, 100);
cout<<"\nEnter first string: ";
cin.getline(str1, 100);
cout<<"Enter second string: ";
cin.getline(str2,100);
str_cat(str1, str2);
break;
case 5: cin.getline(str1, 100);
cout<<"\nEnter string: ";
cin.getline(str1, 100);
str_rev(str1);
break;
case 6: cin.getline(str1, 100);
cout<<"\nEnter string: ";
cin.getline(str1, 100);
str_palin(str1);
break;
case 7: cin.getline(str1, 100);
cout<<"\nEnter first string: ";
cin.getline(str1, 100);
cout<<"Enter second string: ";
cin.getline(str2, 100);
if(str_len(str1)>=str_len(str2))
sub_str(str1, str2);
else
sub_str(str2, str1);
break;
case 8: exit(0); break;
default: cout<<"\nInvalid choice"; break;
}
}
return 0;
}