Custom implementation String Functions

// string functions implemented independent 
#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
////////////////////// ////////////////////////////////////////////////// ////////////////////////////////////////////////// //////////////// 
void myStrrev (char * P) {// string reversal 
    int length = strlen (P); 
    int tmp = 0; 
    for (int I = 0; I <length / 2; I ++) { 
       tmp = P [I]; 
       P [I] = P [I-length-. 1]; 
       P [-length-I. 1] = tmp; 
    } 
} 
void main11 () {/ / string reversal 
    char STR [18 is] = "China Great IS"; 
    // strrev (STR); 
    myStrrev (STR); 
    the printf ( "% S \ n-", STR); // Si anihC taerg 

}
////////////////////////////////////////////////// ////////////////////////////////////////////////// ////////////////////////////////////// 
// string case conversion 
void myStrupr (char * P) { 
    ! the while (* P = '\ 0') { 
        IF (* P> = 'A' && * P <= 'Z') { 
            * P = * P - 32; 
        } 
        P ++; 
    } 
} 
void myStrlwr ( char * P) { 
    ! the while (* P = '\ 0') { 
        IF (* P> = 'A' && * P <= 'the Z') { 
            * P = * P + 32; 
        } 
        P ++; 
    } 
} 
void main12 () {// string case conversion 
    char STR [18 is] = "China Great IS"; 
    // strupr (STR);
    myStrupr (str);
    the printf ( "% S \ n-", STR); the IS GREAT CHINA // 
    // strlwr (STR); 
    myStrlwr (STR); 
    the printf ( "% S \ n-", STR); // China Great IS 
} 

/// ////////////////////////////////////////////////// ////////////////////////////////////////////////// /////////////////////////////////// 
int myStrlen (char * P) {// find the string length 
    int I = 0; 
    the while (! * P = '\ 0') { 
        P ++; 
        I ++; 
    } 
    return I; 
} 
void main13 () {// find the string length 
    char STR [18 is] = "China IS Great"; 
    the printf ( "% D \ n-", strlen (STR)); // 14 
    the printf ( "% D \ n-", myStrlen (STR)); // 14 
}

////////////////////////////////////////////////// ////////////////////////////////////////////////// ////////////////////////////////////// 
void myStrcpy (dest char *, char * Source) { // string copy request 
    IF (dest == NULL || Source == NULL) { 
        return; 
    } {the else 
        the while (Source = NULL!) { 
            * Source * = dest; 
            dest ++; 
            Source ++; 
        } 
        * dest = '\ 0 '; dest // [0] =' \ 0 '; 
    } 
} 
void main14 () {// find string copy 
    char str1 [18 is] = "China Great IS"; 
    char str2 [20 is]; 
    // strcpy (str2 , str1); 
    myStrcpy (str2, str1); 
    the printf ( "% S \ n-", str2);//China is great
}


//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void myStrcat(char *dest, char*source){   //求字符串连接
    if(dest == NULL || source == NULL){
        return;
    } else{
        //char *p =(char *) realloc(dest,strlen(dest)+strlen(source)+1);
        int destLen = strlen(dest);
        dest = dest +destLen;
        while (*source != '\0'){
            *dest =*source;
            dest++;
            source++;
        }
        *dest = '\0';   //dest[0] = '\0';
    }
}
void main15(){   //求字符串连接
    char str1[18] ="China is";
    str2 char [20 is] = "Great"; 
    // strcat (str1, str2); 
    myStrcat (str1, str2); 
    the printf ( "% S \ n-", str1); // China Great IS 
} 

////// ////////////////////////////////////////////////// ////////////////////////////////////////////////// ////////////////////////////// 
char * myStrchr (char * str, char CH) {// Find character 
   while (* str ! = '\ 0') { 
       IF (STR * == CH) { 
           return STR; 
       } 
       STR ++; 
   } 
    return NULL; 
} 
void main16 () {// find the character 
    char STR [18 is] = "China Great IS"; 
    char = CH 'A'; 
    char * P = the strchr (STR, CH); // find its return position, Van not found return NULL 
    the printf ( "% S \ n-", P);//a is great
    myStrchr = P (STR, CH);  
    the printf ( "% S \ n-", P);//a is great
} 

//////////////////////////////////////// ////////////////////////////////////////////////// ////////////////////////////////////////////// 
int myStrcmp (char * str1, char * str2) { // character compare 
   the while (* * str1 == str2) { 
       IF (* str1 == '\ 0' && * str2 == '\ 0') { 
           return 0; 
       } 
       str1 ++; 
       str2 ++ ; 
   } 
    return -1; 
} 
void main17 () {// character comparison 
    char * str1 = "China Great IS"; 
    char * str2 = "China Great IS"; 
/ * IF (str1 == str2) {// C language such string can not compare, str1 str2 and address are 
        the printf ( "equality"); 
    } * / 
    IF (strcmp (str1,str2) == 0) { 
        the printf ( "equality"); 
    } 
    IF (myStrcmp (str1, str2) == 0) { 
        the printf ( "equality"); 
    } 

} 


///////////////////// ////////////////////////////////////////////////// ////////////////////////////////////////////////// /////////////// 
char * myStrstr (str1 char *, char * str2) {// find the string may be represented by the following table method, an array manner 
    char * p = str1 ; // initialize pointer can void * p; void pointer type can be converted to any type 
    // char * P = (char *) P; 
    char * str2 = str2Begin; 
    the while (* str1 = '\ 0'!) { 
        p = str1; // to preserve the position of the first character in str1 str2 appearing in later return 
        str2 = str2Begin; // 
        the while (* str2 str1 == * || * str2 == '\ 0') {// * str2 == '\ 0 ' to the last bit of the data comparison, can enter if Analyzing returns p, into an infinite loop to prevent 
             if (* str2 == '\ 0 ') {
                 P return; 
             } 
            str2 ++; // str1 str2 and the first character is equal to the backward movement continues 
            str1 ++; 
        } 
        str1 = P; // Do not miss this step, in the process of the sub-string comparison, has str1 moving back a big 
        str1 ++; // not found on the main stream continues to move back 

    } 

} 
void main () {// find the string 
    char * str1 = "Great Chiniiss iS"; 
    char * str2 = "iS" ; 
    char * P = Strstr (str1, str2); 
    the printf ( "% S \ n-", P); 
    char * = myStrstr the myP (str1, str2); 
    the printf ( "% S \ n-", the myP); 
}