使用指针算法将数组元素更改为用户输入

Question

I am trying to ask the user for 3 different strings, if the second string is a part of the first string it will replace that part with the third string. In addition to this, I must use pointer arithmetic to index through any arrays/strings. For example:

string1 = foobar  
string2 = oba  
string3 = 12345   
output = fo12345r

My program works when the pattern string (string2) and the replacement string (string3) are the same lengths, but if not I get weird results.

For example:

s1: foobar  
s2: obar  
s3: 3333  
r: fo3333 

(^works)

s1: foobar  
s2: obar  
s3: 33  
r: fo33  ends without including the original last 2 characters ('a','r')  

(^doesn't work)

s1: foobar  
s2: obar  
s3: 12345  
r: fo1234  ends without including the last new character ('5')  

(^doesn't work)

#include <stdio.h>

void GetString(char *str);
void StringReplace(char *original, char *pattern, char *replacement);

int main(void){
    char originalstring[256];
    char patternstring[32];
    char replacement[32];

    printf("Please enter the original string:\n");
    GetString(originalstring);

    printf("Please enter the pattern:\n");
    GetString(patternstring);

    printf("Please enter the replacement:\n");
    GetString(replacement);

    StringReplace(originalstring, patternstring, replacement);
    printf("The Resultant string is %s\n", originalstring);
}


void StringReplace(char *original, char *pattern, char *replacement){
    for(int i = 0; *(original + i) != '\0'; i++){
        if(*(pattern) == *(original + i)){
            for(int x = 0; *(pattern + x) == *(original + i + x);  x++){
                if(x == 1){  
                    *(original + i + (x - 1)) = *(replacement + (x - 1));
                    *(original + i + x) = *(replacement + x);
                }
                if(x >= 2){
                    *(original + i + x) = *(replacement + x);
                }
            }
        }
    }
} // this is supposed to replace the pattern string with the replacement string if they have 2 or more similar characters in succession

Answer 1

You check some of the conditions., If pattern string was found in the original string, then check size_of(s2) with size_of(s3). if s3 >= s2, then simply remove pattern string from original string and replace it with s3. Else case find the size difference between s3 and s2 and then remove pattern string from original string only with that size difference..Finally replace that place with s3.Hope This might helps:)