STRING-STR -PAT -REP

 

STRING

STR, PAT, REP

QUESTION :

Develop a Program in C for the following operations on Strings.

1. Read a main String (STR), a Pattern String (PAT) and a Replace String (REP)

2. Perform Pattern Matching Operation: Find and Replace all occurrences of PAT in STR with REP if PAT exists in STR. Report suitable messages in case PAT does not exist in STR

Support the program with functions for each of the above operations. Don't use Built-in functions.

EXPLANATION :

Here is a C program that performs the operations you've described:

• Reads a main string (STR)

• Reads a pattern string (PAT)

• Reads a replace string (REP)

• Replaces all occurrences of PAT in STR with REP (if PAT exists)

• Uses functions for each operation

• Does not use any built-in string functions like strcpy, strlen, etc.

PROGRAM:

#include <stdio.h>

#define MAX 1000

// Function to calculate length of a string

int stringLength(char str[]) {

int length = 0;

while (str[length] != '\0') {

length++;

}

return length;

}

// Function to check if PAT matches STR at position index

int isMatch(char str[], char pat[], int index) {

int i = 0;

while (pat[i] != '\0') {

if (str[index + i] != pat[i])

return 0;

i++;

}

return 1;

}

// Function to copy part of a string from source to destination

void copyString(char dest[], char src[], int *destIndex, int srcStart, int srcEnd) {

for (int i = srcStart; i < srcEnd; i++) {

dest[*destIndex] = src[i];

(*destIndex)++;

}

}

// Function to perform find and replace

void findAndReplace(char str[], char pat[], char rep[], char result[]) {

int i = 0, resIndex = 0;

int found = 0;

int patLen = stringLength(pat);

int strLen = stringLength(str);

while (i < strLen) {

if (isMatch(str, pat, i)) {

// Pattern match found

found = 1;

// Copy replacement string to result

int j = 0;

while (rep[j] != '\0') {

result[resIndex++] = rep[j++];

}

i += patLen; // Skip the pattern

} else {

// Copy current character

result[resIndex++] = str[i++];

}

}

result[resIndex] = '\0'; // Null terminate

if (!found) {

printf("Pattern not found in the main string.\n");

} else {

printf("Resulting String after Replacement: %s\n", result);

}

}

// Main function

int main() {

char str[MAX], pat[MAX], rep[MAX], result[MAX * 2]; // result might be larger

printf("Enter the main string (STR): ");

fgets(str, MAX, stdin);

printf("Enter the pattern string (PAT): ");

fgets(pat, MAX, stdin);

printf("Enter the replacement string (REP): ");

fgets(rep, MAX, stdin);

// Remove newline characters from input if any

int len;

len = stringLength(str);

if (str[len - 1] == '\n') str[len - 1] = '\0';

len = stringLength(pat);

if (pat[len - 1] == '\n') pat[len - 1] = '\0';

len = stringLength(rep);

if (rep[len - 1] == '\n') rep[len - 1] = '\0';

findAndReplace(str, pat, rep, result);

return 0;

}

OUTPUT-1

Replace a string - main string given/matched

ceciot@cec-IOT:~$ cd Desktop/

ceciot@cec-IOT:~/Desktop$ gcc string.c -o abcd

ceciot@cec-IOT:~/Desktop$ ./abcd

Enter the main string (STR): social work

Enter the pattern string (PAT): social

Enter the replacement string (REP): hard

Resulting String after Replacement: hard work

----------------------------------------------------------------------------------------------------------

OUTPUT-2

Replace a string - main string not matched

ceciot@cec-IOT:~$ cd Desktop/

ceciot@cec-IOT:~/Desktop$ gcc string.c -o abcd

ceciot@cec-IOT:~/Desktop$ ./abcd

Enter the main string (STR): thank you

Enter the pattern string (PAT): good

Enter the replacement string (REP): how

Pattern not found in the main string.