C: Search vor endindex of first occurence - c

Question

how can i write following programm:
• a function which searches a string in a second string and returns the endindex of the first occurence
• a function which includes all occurences of the first string in the second string, which will be replaced by a third string
• a main function which scans the three strings and puts the string out within the replacement
it is not allowed to use more headers than stdio.h , stdlib.h and string.h
i could only start with a code like this, as you can see i couldnt solve any of the three problems. i hope you can help me.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int endIdx(char *string1, char *string2, char *occu)
{
for (int i = 0; i < strlen(string1); i++)
{
for (int j = 0; j < strlen(string1); j++)
{
if (string1[i] == string2[j])
{
printf("occurence string1[%d] is in string2[%d]\n", i, j);
occu[j] = string1[i];
}
}
}
return 0;
}
int main()
{
char string1[20];
char string2[20];
char occu[20];
printf("Type in the first string: ");
scanf("%s", string1);
printf("Type in the second string: ");
scanf("%s", string2);
endIdx(string1, string2, occu);
printf("%s\n", occu);
}

Answer 1

The following program uses strstr to implement your endIdx-problem.
strstr returns a pointer to the first occurrence of searchTeram in str, or NULL, if it does not occur.
In the first case, we get a start index by taking occurrence - str, i.e. the memory address of the first occurrence minus the memory address where str starts. Adding then the length of searchTerm gives the end index.
In the second case, we simply return -1:
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
long endIdx(const char *str, const char *searchTerm) {
long result = -1;
const char* occurrence = strstr(str,searchTerm);
if (occurrence != NULL) {
result = (occurrence - str) + strlen(searchTerm);
}
return result;
}
int main(void)
{
// ----------------012345678901234
const char* str = "Hello world! world is beautiful!";
const char* searchTerm = "world";
long endidx = endIdx(str, searchTerm);
printf("endidx (should be 11): %ld\n", endidx);
endidx = endIdx(str, "not to be contained");
printf("endidx (should be -1): %ld\n", endidx);
return 0;
}