Strings in C In general, a string is a sequence of characters that we index from
ID: 3869936 • Letter: S
Question
Strings in C
In general, a string is a sequence of characters that we index from [0, length-1], where length is the number of characters in the sequence. A sub-string is then the sequence of characters in found between a given start index and a given end index, where 0 <= start <= end and end <= length-1. Given two strings S1 and S2, one may wish to determine is say S2 is a sub-string of S1, and if so where it starts in S1.
First, you are given the contents of the file main.c (which is incomplete):
#include
#include
typedef unsigned int index_t;
int index_of(const char* str, const char* sub_str);
int index_of_from(const char* str, index_t start_index,
const char* sub_str);
int main()
{
char sent[] = "This lab is fun";
char word1[] = "This";
char word2[] = "is";
char word3[] = "fun";
char word4[] = "bun";
char word5[] = "funny";
printf(" Sentence to search : %s ", sent);
int ss_loc = index_of(sent, word1);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word1, ss_loc);
ss_loc = index_of(sent, word2);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word2, ss_loc);
ss_loc = index_of(sent, word3);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word3, ss_loc);
ss_loc = index_of(sent, word4);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word4, ss_loc);
else
printf(""%s" was not found ", word4);
ss_loc = index_of(sent, word5);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word5, ss_loc);
else
printf(""%s" was not found ", word5);
return 0;
}
// if sub_str exists as a sub-string in the string str
// return the starting index of the “left-most” occurrence;
// otherwise return -1
int index_of(const char* str, const char* sub_str)
{
// your code here
}
// if sub_str exists as a sub-string in the string (str + start_index)
// return the starting index of the “left-most” occurrence;
// otherwise return -1
int index_of_from(const char* str, index_t start_index,
const char* sub_str)
{
// your code here
}
First, you will need to write the body for the function :
index_of
Such that when all the files are in one directory (in UNIX) typing
gcc -Wall main.c
followed by
./main
Will produce the following output:
$ gcc -Wall main.c
$ ./main
Sentence to search : This lab is fun
"This" found starting at index : 0
"is" found starting at index : 2
"fun" found starting at index : 12
"bun" was not found
"funny" was not found
Second, copy the body of your index_of function into the body of the index_of_from function and think about what lines of code will need to be added to meet its specifications. Note: you can do it by adding a single “new” first line of code, but also worry about an obvious error that then may occur and how to avoid it.
Explanation / Answer
Here is the program as per your requirements.
The output is also attached.
#include <stdio.h>
#include <string.h>
typedef unsigned int index_t;
int index_of(const char* str, const char* sub_str);
int index_of_from(const char* str, index_t start_index,
const char* sub_str);
int main()
{
char sent[] = "This lab is fun";
char word1[] = "This";
char word2[] = "is";
char word3[] = "fun";
char word4[] = "bun";
char word5[] = "funny";
//int ss_loc ;
printf(" Sentence to search : %s ", sent);
int ss_loc = index_of(sent, word1);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word1, ss_loc);
ss_loc = index_of(sent, word2);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word2, ss_loc);
ss_loc = index_of(sent, word3);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word3, ss_loc);
ss_loc = index_of(sent, word4);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word4, ss_loc);
else
printf(""%s" was not found ", word4);
ss_loc = index_of(sent, word5);
if ( ss_loc != -1 )
printf(""%s" found starting at index : %d ", word5, ss_loc);
else
printf(""%s" was not found ", word5);
ss_loc = index_of_from(sent, 0,word1);
if ( ss_loc != -1 )
printf(""%s" found starting from the given index 0 is : %d ", word1, ss_loc);
ss_loc = index_of_from(sent,2, word2);
if ( ss_loc != -1 )
printf(""%s" found starting from the given index 2 is : %d ", word2, ss_loc);
ss_loc = index_of_from(sent, 0,word3);
if ( ss_loc != -1 )
printf(""%s" found starting from the given index 0 is : %d ", word3, ss_loc);
ss_loc = index_of_from(sent,0, word4);
if ( ss_loc != -1 )
printf(""%s" found starting from the given index 0 is : %d ", word4, ss_loc);
else
printf(""%s" was not found ", word4);
ss_loc = index_of_from(sent, 0,word5);
if ( ss_loc != -1 )
printf(""%s" found starting from the given index 0 is : %d ", word5, ss_loc);
else
printf(""%s" was not found ", word5);
return 0;
}
// if sub_str exists as a sub-string in the string str
// return the starting index of the “left-most” occurrence;
// otherwise return -1
int index_of(const char* str, const char* sub_str)
{
// your code here
int i,j,k,l1,l2,r;
r = -1;
j =0;
l1 = strlen(str);
l2 = strlen(sub_str);
for(i=0; i < l1 ; i++)
{
if( l2 >= i)
{
if(str[i] == sub_str[j])
{
for(k=1; k < l2; k++)
{
if(str[i+k] == sub_str[k])
r = i+1;
else
r = -1;
}
}
}
}
return r;
}
// if sub_str exists as a sub-string in the string (str + start_index)
// return the starting index of the “left-most” occurrence;
// otherwise return -1
int index_of_from(const char* str, index_t start_index,
const char* sub_str)
{
// your code here
int i,j,k,l1,l2,r;
r = -1;
j =0;
l1 = strlen(str);
l2 = strlen(sub_str);
if((start_index + l2) <= l1)
{
for(i=start_index; i < l1 ; i++)
{
if( l2 >= i)
{
if(str[i] == sub_str[j])
{
for(k=1; k < l2; k++)
{
if(str[i+k] == sub_str[k])
r = i-start_index;
else
r = -1;
}
}
}
}
}
return r;
}
Output:
Sentence to search : This lab is fun
"This" found starting at index : 1
"is" found starting at index : 3
"bun" was not found
"funny" was not found
"This" found starting from the given index 0 is : 0
"is" found starting from the given index 2 is : 0
"bun" was not found
"funny" was not found