C++ - does string contain a word - with simple loop? - c++

Question

//EDIT
the code below works only in case that str1 has only 1 beginning letter of str2; how to fix it?
for ex. if str1 / 2 = overflow / flo it works.
but if str1 is overflowfabc (has two "f"s) --> it doesn't work
//
I need to check for a word in a string using simple loop. The idea is:
find an element in str1 that is equal to 1. element of str2
if it exists, we set flag = 1, and it remains 1 if following elements are also equal. If they are not, flag is set to 0.
.
#include <iostream>
using namespace std;
int main() {
string str1, str2;
int flag;
cout << "Enter a string 1: ";
getline(cin, str1);
cout << "Enter a string 2: ";
getline(cin, str2);
for(int i = 0; i < str1.size(); i++)
{
if (str1[i] == str2[0]) // find element in str1 that is equal to first element of str2
{
flag = 1; //
for(int j = i+1; j < i + str2.size(); j++)
if (str1[j] != str2[j-i]) // checking if following elements are also equal
{
flag = 0; // if any of them is not equal
break;
}
if (flag==1)
cout << "str2 is Substring of str1" ;
else
cout << "str2 is NOT Substring" ;
}
}
return 0;
}

Answer 1

bool isSubStr(const string& parent, const string& child)
{
// Check each starting position
for (int i=0; i<(parent.size()-child.size()+1); ++i)
{
// Check if the substring starts at this position
// TODO make this a helper method to avoid the need for a flag
bool isSubString = true;
for (int j=0; j<child.size(); ++j)
{
if (parent[i + j] != child[j])
{
isSubString = false;
break;
}
}
if (isSubString)
{
return true;
}
}
return false;
}

Answer 2

The string class in C++ contains a function named find, and in my opinion you should use that.
The documentation can be found here.
An excerpt about the Return value:
The position of the first character of the first match.If no matches
were found, the function returns string::npos.
#include <iostream>
using namespace std;
int main() {
string str1, str2;
cout << "Enter a string 1: ";
getline(cin, str1);
cout << "Enter a string 2: ";
getline(cin, str2);
size_t found = str1.find(str2);
if (found != string::npos)
cout << "str2 is Substring of str1" << endl;
else
cout << "str2 is NOT Substring" << endl;
return 0;
}
It is shorter and easier to understand. So why not going with that ?
Otherwise I believe your code is not correct in more than one aspect; e.g.
you print out the text depending on the flag variable within the for loop. This does not look right to me.
the second for loop looks strange to me. I believe you are trying to program something that you believe might be considered sophisticated and well thought. To be honest with you, I suggest that do not try to do that. Do simple and clear.
Following your comment I took the time to try to improve your code.
#include <iostream>
using namespace std;
int main() {
string str1, str2;
int flag = 0;
cout << "Enter a string 1: ";
getline(cin, str1);
cout << "Enter a string 2: ";
getline(cin, str2);
for(unsigned int i = 0; i < str1.size(); i++) {
if (str1[i] == str2[0]) { // find element in str1 that is equal to first element of str2
unsigned int j = 0;
for( ; j < str2.size(); j++) {
if ( str1[i+j] != str2[j] ) { // checking if following elements are also equal
break;
}
}
if ( j == str2.size() ) { // if j equals the size of substring then all chars seem equal
flag = 1;
break;
}
}
}
if ( flag )
cout << "str2 is Substring of str1" ;
else
cout << "str2 is NOT Substring" ;
return 0;
}