Trying to compare two strings - c

Question

It is sufficient to say that I am new to C so please have show some mercy ;).
I'm trying to compare two strings. The output shouldn't contain common characters. Sadly it does.
Here is the code:
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
const char msg[15] = "blueberry";
int c;
int s[15];
int j = 0;
int i = 0;
int k= 0;
int ok = 0;
int t = 0;
while (i < 15 && (c = getchar()) != '\n')
{
s[i] = c;
++i;
}
for (t=j=0; t < 15; ++t)
{
ok = 1;
//printf ("%c", s[t]);
}
for (k=0; msg[k] != '\0'; ++k)
{
if (s[t] == msg[k])
{
ok = 0;
}
}
if (ok == 1)
{
s[j] = s[t];
j++;
}
s[j] = '\0';
for (j = 0; j < 15; ++j)
printf ("%c ", s[j]);
}
The input from the keyboard is blackberry, expected output should've been U but sadly it is not. Any help please. Also why is it entering the nested for loop irrespective of condition?
My big thanks to everyone, it helped me a lot. I've figured out a way & am ok with the output. I've borrowed some ideas from A4L :).

Answer 1

To compare two string, you can use strcmp().
The following is a string compare program that you can use for your reference. I has both array and pointer version for better understanding.
#include <stdio.h>
int strcmp1(char a[], char b[])
{
int i=0;
while (a[i] == b[i]) {
if (a[i] == '\0')
return 0;
i++;
}
return a[i]-b[i];
}
int strcmp2(char *a, char *b)
{
while (*a == *b) {
if (*a == '\0')
return 0;
a++; b++;
}
return *a-*b;
}
int main()
{
char s1[] = "test string1";
char s2[] = "test string";
char s3[] = "aaa";
char s4[] = "bbb";
printf("strcmp1(%s, %s) = %d \n", s1, s2, strcmp1(s1, s2));
printf("strcmp2(%s, %s) = %d \n", s3, s4, strcmp2(s3, s4));
return 0;
}

Answer 2

given that msg contains "blueberry" and s contains "blackberry" this should do it
for (int i=0; i < strlen(msg); i++) {
for (int j = 0; j < strlen(s); j++) {
if (msg[i] != s[j]) {
printf ("%c", msg[i]);
}
}
}
yes it's ugly (using the strlen in the for gives me the chills, but I'm still low on coffeine today ^^)

Answer 3

i guess you want to find the first letter where the input differs from message
here is your own code with some fixes
#include <stdio.h>
#include <stdlib.h>
int main(void) {
const char msg[15] = "blueberry";
int c;
char s[15];
int i = 0;
int k= 0;
int ok = 0;
while (i < 15 && (c = getchar()) != '\n')
{
s[i] = (char) c;
++i;
}
// make sure to terminate the string after hitting enter
s[i] = '\0';
printf("input: %s\n", s);
printf("messg: %s\n", msg);
// run through both input and message with one counter
for (k=0; ok == 0 && msg[k] != '\0' && s[k] != '\0'; )
{
// if different chars stop
if (s[k] != msg[k]){
ok = 1;
} else {
// next char
k++;
}
}
if (ok == 1)
{
printf ("diff # index %d -> %c\n", k, msg[k]);
}
else
{
printf ("no diff\n");
}
return 0;
}

Answer 4

#include <stdio.h>
#include <string.h>
//Length to match
int comm(char* s1, char* s2){
int len = 0;
while(*s1 && *s2 && *s1++ == *s2++)
++len;
return len;
}
//commdiffcomm
/*
int commr(char* s1, char* s2){
int len = 0, limit;
int len1,len2;
len1 = strlen(s1);
len2 = strlen(s2);
limit = len1 > len2 ? len2 : len1;
s1 = s1 + len1;
s2 = s2 + len2;
while(limit-- && *--s1 == *--s2)
++len;
return len;
}
//bad
int diff(char* s1, char* s2, int* len1, int* len2){
int len, lenr, s1_len, s2_len, wk_max, i, j;
len = comm(s1, s2);
if(strcmp(s1, s2)==0){
*len1 = *len2 = 0;
return len;
}
lenr = commr(s1, s2);
*len1 = strlen(s1) - len - lenr;
*len2 = strlen(s2) - len - lenr;
return len;
}
*/
int diff(char* s1, char* s2, int* len1, int* len2){
int len, s1_len, s2_len, wk_max, i, j;
len = comm(s1, s2);
if(strcmp(s1, s2)==0){
*len1 = *len2 = 0;
return len;
}
s1_len = strlen(s1 + len + 1);
s2_len = strlen(s2 + len);
wk_max = 0;
for(i = 1; i < s1_len ; i++){
for(j = 0; j < s2_len; j++){
int com_len;
com_len = comm(s1 + len + i, s2 + len + j);
if(wk_max < com_len){
wk_max = com_len;
*len1 = i;
*len2 = j;
}
}
}
return len;
}
int main(){
char str1[16] = "blueberry";
char str2[16] = "blackberry";
char dif1[16] = "";
char dif2[16] = "";
int len0;//length of top to diff pos
int len1;
int len2;
len0 = diff(str1, str2, &len1, &len2);
strncpy(dif1, str1 + len0, len1);
strncpy(dif2, str2 + len0, len2);
if(len1 !=0 && len2 != 0){
printf("%s different %s at position %d length %d (\"%s\")\n", str1, str2, len0, len1, dif1);
printf("%s different %s at position %d length %d (\"%s\")\n", str2, str1, len0, len2, dif2);
} else {
printf("two string is same.");
}
return 0;
}
/*
blueberry different blackberry at position 2 length 2 ("ue")
blackberry different blueberry at position 2 length 3 ("ack")
*/

Answer 5

There are a few problems with the code as is:
You don't null-terminate your input string. Attempting to use it with c string functons would spell trouble. To fix that, change
while (i < 15 && (c = getchar()) != '\n')
{
s[i] = c;
++i;
}
to
while (i < 14 && (c = getchar()) != '\n')
{
s[i] = c;
++i;
}
s[i] = '\0';
Your specification is unclear as to whether you want your program to print the letters unique to msg, or to both s and msg. (i.e, do you want msg-s or (msg ∪ s)-(msg ∩ s) Assuming the first, the important part of your program goes like this:
k=0;
for(i=0;i<strlen(msg);i++){
int exists = 0;
for(j=0;!exists && j<strlen(s);j++){
if(msg[j] == s[i])
exists = 1;
}
if(!exists)
msg[k++] = msg[i];
}
s[k] = '\0';
The inner loop checks if s contains the current character in msg. If it does, we don't do anything, but if it doesn't, we append it to the end of a sublist we're creating on top of the bits of msg we've already processed.

Answer 6

your code is a mess even after the rewrite - there are too many errors to describe in detail
/*
blackbery
b l u e b e r r y
. . a c k b e . .
result = non-equal
*/
#include <stdio.h>
#include <stdlib.h>
int main(void) {
const char msg[15] = "blueberry";
int c, s[15], i,j,k, ok;
for (i=0; i < 15; i++) s[i] = 0;
for (i=0; i < 15 && (c = getchar()) != '\n'; i++) s[i] = c;
for (ok=1, k=0; msg[k] != '\0'; ++k)
if (s[k] != msg[k]) ok = 0; else s[k] = '.';
for (j = 0; j < 15; ++j) printf ("%c ", msg[j]);
printf("\n");
for (j = 0; j < 15; ++j) printf ("%c ", s[j]);
printf("\nresult = %s\n", ok ? "equal" : "non-equal");
}