arrays - Check a string in another string in C++ -

#include <iostream> #include <string> using namespace std;  int main() {     string str_1 = "gandalf";     string str_2 = "dal";     (int = 0; <= str_1.length() - 2; i++)         (int j = 0; j <= str_2.length(); j++) {             if (str_2[j] == str_1[i]) {                 if (str_2[j + 1] == str_1[i + 1]) {                     if (str_2[j + 2] == str_1[i + 2])                         cout << "true";                 }             }         }     return 0; } 

i can if length of str_2 4 characters, program doesn't work. want program can work every length of string how?

the function find below reproduces behaviour of std::string::find (without starting position parameter). need to:

• loop through outer string, , @ each step:
• loop through second string checking each character.
• if of these fail, drop outer loop.
• if make way through inner loop, second string there, , return current position in outer loop.
• if run out of space in first string, skip rest.

hopefully comments make clear. include little utility function turn found position true/false, , tests.

#include <iomanip> #include <iostream> #include <string>  std::string::size_type find(const std::string& s1,                             const std::string& s2)     // return position of s2 within s1,     // else npos if not present. {     using size_type = std::string::size_type;     size_type curpos = 0;     size_type lim    = s1.size();     size_type innerlim = s2.size();      (; curpos<lim; ++curpos) { // loop through s1         if (lim < curpos+innerlim) {             break; // not enough space left         }         size_type innerpos = 0;         for(; innerpos < innerlim // loop through s2, while matching                 && curpos + innerpos < lim                 && s1[innerpos+curpos] == s2[innerpos];                 ++innerpos) ; // nothing in loop         if (innerpos == innerlim) { // matched whole loop             return curpos;         }     }     return std::string::npos; // never matched }  bool contains(const std::string& s1,               const std::string& s2) {     return find(s1, s2)!=std::string::npos; }   int main() {     std::cout         << std::boolalpha         << contains("abc", "")      << '\n' // true         << contains("abc", "abc")   << '\n' // true         << contains("abc", "bc")    << '\n' // true         << contains("abc", "abcd")  << '\n' // false         << contains("abc", "abd")   << '\n' // false         << contains("abc", "xyz")   << '\n';// false } 

this more need, closely models "real" answer (use facilities language provides). plus makes not great homework answer, contains clues write homework answer.