Remove comments from a given C/C++ program (original) (raw)

Last Updated : 31 Jan, 2023

Given a C/C++ program, remove comments from it.

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The idea is to maintain two flag variables, one to indicate that a single line comment is started, another to indicate that a multiline comment is started. When a flag is set, we look for the end of comment and ignore all characters between start and end.

Following is C++ implementation of above idea.

C++ `

// C++ program to remove comments from a C/C++ program #include using namespace std;

string removeComments(string prgm) { int n = prgm.length(); string res;

// Flags to indicate that single line and multiple line comments
// have started or not.
bool s_cmt = false;
bool m_cmt = false;


// Traverse the given program
for (int i=0; i<n; i++)
{
    // If single line comment flag is on, then check for end of it
    if (s_cmt == true && prgm[i] == '\n')
        s_cmt = false;

    // If multiple line comment is on, then check for end of it
    else if  (m_cmt == true && prgm[i] == '*' && prgm[i+1] == '/')
        m_cmt = false,  i++;

    // If this character is in a comment, ignore it
    else if (s_cmt || m_cmt)
        continue;

    // Check for beginning of comments and set the appropriate flags
    else if (prgm[i] == '/' && prgm[i+1] == '/')
        s_cmt = true, i++;
    else if (prgm[i] == '/' && prgm[i+1] == '*')
        m_cmt = true,  i++;

    // If current character is a non-comment character, append it to res
    else  res += prgm[i];
}
return res;

}

// Driver program to test above functions int main() { string prgm = " /* Test program / \n" " int main() \n" " { \n" " // variable declaration \n" " int a, b, c; \n" " / This is a test \n" " multiline \n" " comment for \n" " testing */ \n" " a = b + c; \n" " } \n"; cout << "Given Program \n"; cout << prgm << endl; cout << " Modified Program "; cout << removeComments(prgm); return 0; }

`

Output

Given Program /* Test program / int main()
{
// variable declaration int a, b, c;
/ This is a test
multiline
comment for
testing */
a = b + c;
}

Modified Program
int main()
{
int a, b, c;

  a = b + c;       

}

Time Complexity :O(N), where N is length of string.

Space Complexity: O(1), since no extra space used.