C string operation functions

C string operation functions

 

 

1. String inversion-strrev

2. Copy strings-strcpy

3. Convert the string to an integer-atoi

4. String Length-strlen

5. String connection-strcat

6. String comparison-strcmp

7. Calculate the number of vowels in a string.

8. Determine whether a string is a text return.

 

1. Write a function to reverse the string

 

Version 1-while

 

Void strrev (char * s)

{

Char temp, * end = S + strlen (S)-1;

While (end> S)

{

Temp = * s;

* S = * end;

* End = temp;

-- End;

++ S;

}

}

 

Version 2-

 

Void strrev (char * s)

{

Char temp;

For (char * end = S + strlen (S)-1; end> S; -- end, ++ S)

{

Temp = * s;

* S = * end;

* End = temp;

}

}

 

Version 3-no third-party Variables

 

Void strrev (char * s)

{

For (char * end = S + strlen (S)-1; end> S; -- end, ++ S)

{

* S ^ = * end;

* END ^ = * s;

* S ^ = * end;

}

}

 

Version 4-rebuilding Version 3

 

Void strrev (char * s)

{

For (char * end = S + strlen (S)-1; end> S; -- end, ++ S)

{

* S ^ = * END ^ = * s ^ = * end;

}

}

 

Version 5-rebuilding version 4

 

Void strrev (char * s)

{

For (char * end = S + strlen (S)-1; end> S; * s ++ ^ = * END ^ = * s ^ = * end --);

}

 

Version 6-recursive version

 

Void strrev (const char * s)

{

If (s [0] = '\ 0 ')

Return;

Else

Strrev (& S [1]);

Printf ("% C", s [0]);

}

 

 

2. Implement the strcpy function of the database.

 

The strcpy function is located in the header file <string. h>.

 

Version 1

 

Strcpy (char * DEST, const char * SRC)

{

Char * P = DEST;

While (* DEST ++ = * SRC ++)

;

DeST = P;

}

 

Version 2

 

Char * _ cdecl strcpy (char * DST, const char * SRC)

{

Char * P = DST;

While (* P ++ = * SRC ++)

;

Return DST;

}

 

Version 3

 

Strcpy (char * DEST, const char * SRC)

{

Int I = 0;

For (; * (SRC + I )! = '\ 0'; I ++)

* (DEST + I) = * (SRC + I );

* (DEST + I) = '\ 0 ';

}

 

 

3. Implement the atoi function of the library function

 

The atoi function is located in the header file <stdlib. h>.

 

Version 1-Appendix

 

Int power (INT base, int exp)

{

If (0 = exp)

Return 1;

Return base * power (base, exp-1 );

}

 

Int _ cdecl atoi (const char * s)

{

Int exp = 0, n = 0;

Const char * t = NULL;

For (; * s = ''| * s = '\ T' | * s =' \ n'; s ++) // find the first non-null character

;

If (* s> '9' | * S <'0') // if the first non-null character is not a numeric character, 0 is returned.

Return 0;

For (t = s; * T> = '0' & * t <= '9'; ++ t) // locate the first non-numeric character position-method 1

;

T --;

 

/* Locate the first non-numeric character location-method 2

T = s;

While (* t ++> = '0' & * t ++ <= '9 ')

;

T-= 2;

*/

 

While (T> = s)

{

N + = (* t-48) * power (10, exp); // convert numeric characters to Integers

T --;

Exp ++;

}

Return N;

}

 

Version 2

 

Int _ cdecl atoi (const char * s)

{

Int exp = 0, n = 0;

Const char * t = NULL;

For (; * s = ''| * s = '\ T' | * s =' \ n'; s ++) // skip non-null characters

;

If (* s> '9' | * S <'0 ')

Return 0;

For (t = s; * T> = '0' & * t <= '9'; ++ T)

;

T --;

 

While (T> = s)

{

N + = (* t-48) * POW (10, exp );

T --;

Exp ++;

}

Return N;

}

 

 

4. Implement the strlen function of the library function

 

The strlen function is located in the header file <string. h>.

 

Version 1-while

 

Size_t _ cdecl strlen (const char * s)

{

Int I = 0;

While (* s)

{

I ++;

S ++;

}

Return I;

}

 

Version 2-

 

Size_t _ cdecl strlen (const char * s)

{

For (INT I = 0; * s; I ++, s ++)

;

Return I;

}

 

Version 3-variable-Free Edition

 

Size_t _ cdecl strlen (const char * s)

{

If (* s = '\ 0 ')

Return 0;

Else

Return (strlen (++ s) + 1 );

}

 

Version 4-rebuilding Version 3

 

Size_t _ cdecl strlen (const char * s)

{

Return * s? (Strlen (++ s) + 1): 0;

}

 

 

5. Implement the strcat function of the library function

 

The strcat function is located in the header file <string. h>.

 

Version 1-while

 

Char * _ cdecl strcat (char * DST, const char * SRC)

{

Char * P = DST;

While (* P)

P ++;

While (* P ++ = * SRC ++)

;

Return DST;

}

 

 

6. Implement the strcmp function of the Database Function

 

The strcmp function is located in the header file <string. h>.

 

Version 1-invalid strcmp

 

Int strcmp (const char * a, const char * B)

{

For (; *! = '\ 0' & * B! = '\ 0'; A ++, B ++)

If (* A> * B)

Return 1;

Else if (* A = * B)

Return 0;

Else

Return-1;

}

 

Version 2

 

Int _ cdecl strcmp (const char * SRC, const char * DST)

{

Int ret = 0;

 

While (! (Ret = * (unsigned char *) Src-* (unsigned char *) DST) & * SRC)

++ SRC, ++ DST;

 

If (Ret <0)

Ret =-1;

Else if (Ret> 0)

Ret = 1;

 

Return (RET );

}

 

 

7. Calculate the number of metainfo characters in a string

 

# Include <stdio. h>

 

Int is_vowel (char)

{

Switch ()

{

Case 'A ':

Case 'E ':

Case 'I ':

Case 'O ':

Case 'U ':

Return 1; break;

Default:

Return 0; break;

}

}

 

Int count_vowel (const char * s)

{

Int num;

If (s [0] = '\ 0 ')

Num = 0;

Else

{

If (is_vowel (s [0])

Num = 1 + count_vowel (& S [1]);

Else

Num = count_vowel (& S [1]);

}

Return num;

}

 

Int main ()

{

Char * s = "aobcd ddudie ";

Printf ("% d \ n", count_vowel (s ));

Return 0;

}

 

 

8. judge whether a string contains a word or a phrase without spaces or punctuation. For example, Madam I'm Adam is a echo.

 

Version 1

 

/*

*ProgramFunction: determines whether a word or phrase without spaces or punctuation is palindrome)

*/

# Include <stdio. h>

# Include <ctype. h>

 

Int is_palindrome (const char * s)

{

Bool is_palindrome = 0;

Const char * end = s;

 

If (* end = '\ 0')/* If s is an empty string, it is a reply */

Is_palindrome = 1;

 

While (* End) + + end;/* end points to the last character position of string S */

-- End;

 

While (S <= end)

{

While (* s = ''|! Isalpha (* s)/* omitted non-letter characters in string S */

++ S;

While (* end = ''|! Isalpha (* End ))

-- End;

If (toupper (* S) = toupper (* End)/* converts the letter character in s to a big character for judgment */

{

++ S;

-- End;

}

Else

{

Is_palindrome = 0; break;

}/* Under the S <= end condition, if there is an inequality, the system determines that S is not a return object */

}

If (S> end)

Is_palindrome = 1;

Else

Is_palindrome = 0;

Return (is_palindrome );

 

}

 

Int main ()

{

Const char * s = "Madam I'm Adam ";

Printf ("% S % s \ n", S, is_palindrome (s )? "Is a palindrome! ":" Is not a palindrome! ");

Return 0;

}