need help! replacing substing in a string with another substring

[sandvet03]

I am trying to expand on a earlier program for counting subs and now i am trying to replace substrings within a given string. For example if the main string was "The cat in the hat" i am trying to find a chosen substring lets say "cat" and then replace it with a difrent inputed substring say "dog". Tried to get as far as i could on my own but need some help, sugestions, snippets or guidence.

# include<stdio.h>  
# include<math.h>
# include<stdlib.h>
# include<string.h>
 
int main(void)
 
{
 
char s[200], old[75], new[25];
char newstr[200];
char *newtsr=NULL;
 
char count;
int count2;
int run;
int i;
int j;
int strstrcnt(const char *s,const char *old);
char *replace(const char *s, const char *old, const char *new);    
printf("\nThis is a program to find certian occurances of words in a user inputed sentence\n");
printf("\nIt will display the number of times the word is found.\n");
 
printf("\nTo run this program and input the word to find and the sentence to search hit 1,\n\n Hit 2 to exit.\n");
printf("\nHit 4 to find a word then replace it/n");
scanf("%d",&run);
 
fflush(stdin);
 
while (run==1)
 
{printf("\nPlease input the sentence you wish to hae searched.\n");
 
 gets(s);
 
 printf("\nPlease enter the word or term you wish to have found in the sentence.\n");
 
 gets(old);
 
 fflush(stdin);
 
 count=strstrcnt(s,old);
 
 printf("There is %d instances of the selected word in the sentence.\n\n %s\n\n",count,s);
 printf("Hit 2 to exit 1 to continue, Hit 3 to ignore case sensitivity.Hit 4 to replace the word.\n\n");
 fflush(stdin);
 scanf("%d",&run);
 
 
while (run==3)
{  strupr(s)newstr = replace(s,new,old);;
   strupr(old);
   count=strstrcnt(s,old);
 
 
 printf("There is %d instances of the selected word in the sentence.\n\n %s\n\n",count,s);
 printf("Hit 2 to exit, 1 to continue, 3 to run non case sensitive again.\n\n");
 fflush(stdin);
 scanf("%d",&run);
 
                  }
while (run==4)
{printf("\n Please enter the new string to replace the old words\n");
 
    scanf("%s",&new);
    fflush(stdin);
   newstr = replace(s,new,old);
   printf("%s",newstr);
   printf("\nPlease hit 1 to continue\n");
   scanf("%d",&run);
   fflush(stdin);
}}
return(0);}newstr = replace(s,new,old);
 
int strstrcnt(const char *s,const char *old)
{  int i;
   char *q;//pointer
   int count=0;
int length=strlen(old); 
   for (i=0;i<length;i++)
   q=strstr(s,old);
   while (q!= NULL)
   {q=strstr(q+1,old);
       count++;}//counter
 
return count;}
 
char *replace(const char *s, const char *old, const char *new)
{
char *ret, *sr;
size_t i, count = 0;
size_t newlen = strlen(new);
size_t oldlen = strlen(old);
 
if (newlen != oldlen) {
for (i = 0; s[i] != '\0'; ) {
if (memcmp(&s[i], old, oldlen) == 0)
count++, i += oldlen;
else
i++;
}
} else
i = strlen(s);
 
ret = malloc(i + 1 + count * (newlen - oldlen));
if (ret == NULL)
return NULL;
 
sr = ret;
while (*s) {
if (memcmp(s, old, oldlen) == 0) {
memcpy(sr, new, newlen);
sr += newlen;
s += oldlen;
} else
*sr++ = *s++;
}
*sr = '\0';
 
return ret;
}
 
 

has two errors when compiling and crashes if ran
the errors are
|75 error 8004| 'newtsr' is assigned a value that is never used in function main
|69 error 2277| Lvalue required in function main

NOTE: This is me trying to better understand C and explore what it can do.

[gpraghuram]

I havent looked into the code fully.
But what logic r u using in the replace function.
Logic should be
1)You should know the position where u are going to replace
2)From position 0 to the matched position copy original string
3)Form matched position copy the replace string
4)From the last copied position copy the remaining original string

take care you allocate enough memory for the final string

Raghuram

[mmk]

I havent looked into the code fully.
But what logic r u using in the replace function.
Logic should be
1)You should know the position where u are going to replace
2)From position 0 to the matched position copy original string
3)Form matched position copy the replace string
4)From the last copied position copy the remaining original string

take care you allocate enough memory for the final string

Raghuram

Even I have gon through the logic but its totally messed but. Anyway what Raghu suggest is great approach.

One more approach can be.

I assume the input string is a single line.

Data structures required : newstr,tempstr,searchstring,oldstr of string type

1. Read line into "oldstr".
2. Read the string to change into "serachstring".
3. Now traverse from postion 0 to \n in oldstr searching for "searchstring". while traversing copy the contents traversed to tempstr.
4. If first character of any string matches. Use strcmp to compare searchstring and foundstring (from pointer position in old str till \0).
5. Based on strcmp return value, if string found, append searchstring to newstr and copy the rest oldstr string to newstr till oldstr \n is reached.

oldstr = "the cast is in hat"
searchstring = "dog"
output : newstr = "the dog is in hat"

Raghu please correct me if i am wrong.
There are various approaches to do this.If we are good at string operations basics this will be easy approach to complete the above assignment.

[mmk]

Even I have gon through the logic but its totally messed but. Anyway what Raghu suggest is great approach.

One more approach can be.

I assume the input string is a single line.

Data structures required : newstr,tempstr,searchstring,oldstr of string type

1. Read line into "oldstr".
2. Read the string to change into "serachstring".
3. Now traverse from postion 0 to \n in oldstr searching for "searchstring". while traversing copy the contents traversed to tempstr.
4. If first character of any string matches. Use strcmp to compare searchstring and foundstring (from pointer position in old str till \0).
5. Based on strcmp return value, if string found, append searchstring to newstr and copy the rest oldstr string to newstr till oldstr \n is reached.

oldstr = "the cast is in hat"
searchstring = "dog"
output : newstr = "the dog is in hat"

Raghu please correct me if i am wrong.
There are various approaches to do this.If we are good at string operations basics this will be easy approach to complete the above assignment.

Sorry i forgot "string to replace" in data structure and in logic . Here modified algorithm

Data structures required : newstr,tempstr,searchstring,replacestr,oldstr of string type

1. Read line into "oldstr".
2. Read the string to change into "serachstring".
3. Now traverse from postion 0 to \n in oldstr searching for "searchstring". while traversing copy the contents traversed to tempstr.
4. If first character of any string matches. Use strcmp to compare searchstring and foundstring (from pointer position in old str till \0).
5. Based on strcmp return value, if string found, append replacestr to newstr and copy the rest oldstr string to newstr till oldstr \n is reached.

oldstr = "the cast is in hat"
searchstring = "dog"
output : newstr = "the dog is in hat"

[mmk]

Sorry i forgot "string to replace" in data structure and in logic . Here modified algorithm

Data structures required : newstr,tempstr,searchstring,replacestr,oldstr of string type

1. Read line into "oldstr".
2. Read the string to change into "serachstring".
3. Now traverse from postion 0 to \n in oldstr searching for "searchstring". while traversing copy the contents traversed to tempstr.
4. If first character of any string matches. Use strcmp to compare searchstring and foundstring (from pointer position in old str till \0).
5. Based on strcmp return value, if string found, append replacestr to newstr and copy the rest oldstr string to newstr till oldstr \n is reached.

oldstr = "the cast is in hat"
searchstring = "dog"
output : newstr = "the dog is in hat"

Sorry i forgot "string to replace" in data structure and in logic . Here modified algorithm

Data structures required : newstr,tempstr,searchstring,replacestr,oldstr of string type

1. Read line into "oldstr".
2. Read the string to change into "serachstring".
3. Now traverse from postion 0 to \n in oldstr searching for "searchstring". while traversing copy the contents traversed to tempstr.
4. If first character of any string matches. Use strcmp to compare searchstring and foundstring (from pointer position in old str till \0).
5. Based on strcmp return value, if string found, append replacestr to newstr and copy the rest oldstr string to newstr till oldstr \n is reached.

oldstr = "the cast is in hat"
searchstring = "dog"
output : newstr = "the dog is in hat"