For some reason, I can't get this to work! Can anyone tell me where I've gone wrong? This is supposed to reverse the words in a give string (i.e from "this is a test" to "test a is this")
#include <stdio.h>
#include <stdlib.h>
char *reverse(char const *input)
{
char *ret = (char *)malloc(sizeof(char) * strlen(input));
int length = 0;
int numWords = 1;
int i;
for(i=0; input[i]!=NULL; i++)
{
length++;
if(input[i]==' ')
numWords++;
}
char words[numWords];
int currentWord = numWords;
for(i=0; input[i]!=NULL; i++)
{
if (input[i]==' '){
currentWord--;
}else{
words[currentWord] = words[currentWord] + input[i];
}
}
for(i=0; i < numWords; i++)
{
ret = ret + words[i];
}
return ret;
}
int main(int argc, char **argv)
{
int nTestcase = 0;
int i = 0;
char inputstr[100];
char *reversedStr = NULL;
scanf("%d\n", &nTestcase);
for (i = 0; i < nTestcase; i++)
{
fgets(inputstr, 100, stdin);
reversedStr = reverse(inputstr);
printf("%s\n", reversedStr);
free(reversedStr);
memset(inputstr, 0, 100);
}
return 0;
}
words[currentWord] = words[currentWord] + input[i];
You can't add characters to each other like that expecting string concatenation. And I imagine you expect words to be an array of words (i.e. strings), but its type is not that, words is just an array of characters.
Like #Tom said, you're doing this again in the last for loop:
ret = ret + words[i];
Joseph, unlike other programming languages ( c# or PHP ), string handling functions of C are quite basic.
You cannot add strings directly, however there are a host of library functions you can use to accomplish the same task.
Check out,
strtok - Use it to split the string to words. strtok reference
strncat - Use to concatenate strings
strings in C are just byte arrays terminated with the null character ( byte with value 0).
Here is shorter/cleaner way
private char[] reverseWords(char[] words) {
int j = words.length - 1;
for (int i = 0; i < (words.length)/2; i++) {
if(i==j)
continue;
char temp = words[i];
words[i] = words[j];
words[j]=temp;
j--;
}
int lastIndex = 0;
for (int i=0;i<words.length;i++){
if(words[i]==' '){
words = reverseWord(words,lastIndex,i-1);
lastIndex=i+1;
}
}
words = reverseWord(words,lastIndex,words.length-1);
return words;
}
private char[] reverseWord(char[] words, int from, int to) {
int j=to;
for(int i=from;i<((to/2)+from/2);i++){
if(i==j) continue;
char temp = words[j];
words[j]=words[i];
words[i]=temp;
j--;
}
return words;
}
Related
I'm learning C and I've a problem with this school homework.
I have to make function which get two strings from user as parameters. The function removes all spaces from the first string and returns the "cleaned" strings as the other parameter.
The main function ask three strings, uses function to remove spaces and prints "cleaned" strings.
My code doesn't work as it should? What goes wrong?
#include <stdio.h>
void removeSpaces(char *, char *);
int main(){
int i, j;
char string[101], strings[1][101];
for(i = 0; i <= 2; i++){
fgets(string, 100, stdin);
for(j = 0; string[j] != '\0'; j++){
strings[i][j] = string[j];
}
strings[i][j] = '\0';
removeSpaces(strings[i], strings[i]);
}
for(i = 0; i <= 0; i++){
for(j = 0; j <= 101; j++){
printf("%c", strings[i][j]);
}
}
}
void removeSpaces(char *string1, char *string2){
int i, j;
for(i = 0; string1[i] != '\0'; i++){
if(string1[i] != ' '){
string2[i] = string1[j];
j++;
}
}
string2[i] = '\0';
}
You have to be more careful when writing code. There are several things wrong:
In removeSpaces(), you never initialize j. So it can be anything.
You are also mixing up i and j inside removeSpaces(). i should only be used to index string1, and j only for string2.
strings[1][101] is only one string, not 3. But the first for-loop in main() runs 3 times.
You don't have to print strings character by character, just printf("%s", strings[i]) or fputs(strings[i], stdout).
I'm not sure why you used a two-dimensional array strings here. You only need two strings. Renaming the variables can also help you avoid getting confused. Consider:
#include <stdio.h>
static void removeSpaces(const char *input, char *output) {
int i, o;
for(i = 0, o = 0; input[i] != '\0'; i++) {
if(input[i] != ' ') {
output[o] = input[i];
o++;
}
}
output[o] = '\0';
}
int main() {
char input[100], output[100];
fgets(input, sizeof input, stdin);
removeSpaces(input, output);
fputs(output, stdout);
}
Please, help with the code.
Requirement:
Write a function my_union that takes two strings and returns, without doubles, the characters that appear in either one of the strings.
Example:
Input: "zpadinton" && "paqefwtdjetyiytjneytjoeyjnejeyj"
Output: "zpadintoqefwjy"
My code:
#include <stdbool.h>
#include <stdio.h>
#include <string.h>
char *my_union(char *a, char *b) {
char *str;
// Algorithm for excluding nonunique characters from string a(given in
// parameters).
str[0] = a[0];
int k = 1;
str[k] = '\0';
for (int i = 1; a[i] != '\0'; i++) {
bool is = true;
for (int j = 0; str[j] != '\0'; j++) {
if (str[j] == a[i]) {
is = false;
break;
}
}
if (is) {
str[k] = a[i];
k++;
str[k] = '\0';
}
} // In this case we are excluding excess character 'n' from "zpadinton", so
// str is equal to "zpadinto".
// Algorithm for adding unique characters from array b(given in parameters)
// into str.
for (int i = 0; b[i] != '\0'; i++) {
bool is = true;
for (int j = 0; str[j] != '\0'; j++) {
if (str[j] == b[i]) {
is = false;
break;
}
}
if (is) {
strncat(str, &b[i], 1);
}
}
return str;
}
The first algorithm is almost identical with second, but it doesn't work(. Mb I messed up with memory, give some advice, pls.
If you mean, get the unique characters from two strings and store them into a new string, try this code ;
First, you must allocate a memory for str. In your code, str is not pointing allocated memory location, so you will probably get segmentation fault.
int contains(const char * str,char c)
{
for (int i = 0; i < strlen(str); ++i)
if(str[i] == c)
return 1;
return 0;
}
char * my_union(char *a, char*b)
{
char * res = (char*)malloc(sizeof(char)*(strlen(a) + strlen(b)));
int pushed = 0;
for (int i = 0; i < strlen(a); ++i)
{
if(!contains(res,a[i])){
res[pushed] = a[i];
pushed++;
}
}
for (int i = 0; i < strlen(b); ++i)
{
if(!contains(res,b[i])){
res[pushed] = b[i];
pushed++;
}
}
return res;
}
int main(int argc, char const *argv[])
{
char string1[9] = "abcdefgh";
char string2[9] = "abegzygj";
char * result = my_union(string1,string2);
printf("%s\n", result);
return 0;
}
Also, do not forget the free the return value of my_union after you done with it.
I have made two functions that find a substring index and substitute that substring in the string. I'm glad I jury rigged this at all, given that similar questions previously asked were never answered/marked as closed without any help. Is there a cleaner method?
void destroy_substr(int index, int len)
{
int i;
for (i = index; i < len; i++)
{
string[i] = '~';
}
}
void find_substr_index(char* substr)
{
int i;
int j;
int k;
int count;
int len = strlen(substr);
for (i = 0; i < strlen(string); i++)
{
if (string[i] == substr[0])
{
for(j = i, k = 0; k < len; j++, k++)
{
if (string[j] == substr[k])
{
count++;
}
if (count == len)
destroy_substr((j - len + 1), len);
}
j = 0;
k = 0;
count = 0;
}
}
}
Your code seems like you're trying to re-inventing your own wheel.
By using standard C functions, which is strstr() and memset(), you can achieve the same result as you expected.
#include <stdio.h>
#include <string.h>
char string[] = "foobar foobar foobar";
char substr[] = "foo";
char replace = '~';
int main() {
int substr_size = strlen(substr);
// Make a copy of your `string` pointer.
// This is to ensure we can safely modify this pointer value, without 'touching' the original one.
char *ptr = string;
// while true (infinite loop)
while(1) {
// Find pointer to next substring
ptr = strstr(ptr, substr);
// If no substring found, then break from the loop
if(ptr == NULL) { break; }
// If found, then replace it with your character
memset(ptr, replace, substr_size);
// iIncrement our string pointer, pass replaced substring
ptr += substr_size;
}
printf("%s\n", string);
return 0;
}
How about this:
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv)
{
char string[] = "HELLO hello WORLD world HELLO hello ell";
char substring[] = "ell";
int stringLength = strlen(string);
int substringLength = strlen(substring);
printf("Before: %s\n", string);
if(substringLength <= stringLength)
{
int i;
int j;
for(i = 0, j = stringLength - substringLength + 1; i < j; )
{
if(memcmp(&string[i], substring, substringLength) == 0)
{
memset(&string[i], '~', substringLength);
i += substringLength;
}
else
{
i++;
}
}
}
printf("After: %s\n", string);
return 0;
}
Key ideas are:
You only need to scan the string (stringLength - substringLength) times
You can use functions from string.h to do the comparison and to replace the substring
You can copy the new string in place. If you want to support insertion of longer strings you will need to manage memory with malloc()/realloc(). If you want to support insertion of smaller strings you'll need to advance the pointer to the beginning by the length of the replacement string, copy the rest of the string to that new location, then zero the new end of the string.
#include <stdio.h>
#include <string.h>
#include <err.h>
int main(int argc, char **argv)
{
char *str = strdup("The fox jumps the dog\n");
char *search = "fox";
char *replace = "cat";
size_t replace_len = strlen(replace);
char *begin = strstr(str, search);
if (begin == NULL)
errx(1, "substring not found");
if (strlen(begin) < replace_len)
errx(1, "replacement too long");
printf("%s", str);
memcpy(begin, replace, replace_len);
printf("%s", str);
return 0;
}
I'm trying to take a string and break it into "word" components and store that in an array of strings.
"Hello my name is Bill." should give back a char** with elements, "Hello", "my", "name", "is", and "Bill."
My code will compile however I keep encountering a runtime error (I don't get warnings anymore and my debugger gdb doesn't work)>
I'm running on minGW on Window 8.
#include <stdio.h>
#include <stdlib.h>
char** words(char* string)
{
int i = 0;
int j = 0;
int k =0;
int count = 0;
char** stringArray = (char**) malloc(sizeof(char)*30*30);
while( string[i] != '\0' )
{
if(string[i] != ' ')
{
j =0;
while(string[i+j+1] != ' ')
{
j++;
}
i = i+j;
for(k=0; k<=j; k++)
{
stringArray[count][k] = string[i+k];
}
count++;
}
i++;
}
return stringArray;
}
int main()
{
char message[20] = "abcd efgh ijkl mno";
char** wordArray = words(message);
printf("%c\n\n", wordArray[0][0]);
int i =0;
while(wordArray[i])
{
printf("%s\n", wordArray[i]);
i++;
}
printf("\nThe problem is not with the words function");
return 0;
}
There are couple of issues that have been mentioned in the comments.
The allocation should look something like:
#include <ctype.h> // for isspace()
#define MAXSTRLEN 30 // using a symbolic constant
char **stringArray;
int i, j, k;
stringArray = malloc(sizeof(char*) * MAXSTRLEN); // don't cast from malloc
for (i = 0; i < 30; ++i) {
stringArray[i] = malloc(sizeof(char) * MAXSTRLEN);
}
// TODO error checking: malloc could return NULL
while copying the substrings would look like:
i = 0;
j = 0;
while( string[i] != '\0') // go through the whole string
{
while (string[i] != '\0' && isspace(string[i])) {
i++; // skip whitespaces
}
k = 0;
while (string[i] != '\0' && !isspace(string[i])) { // copy word until whitepace or end of string
stringArray[j][k++] = string[i++];
}
stringArray[j][k] = '\0'; // EOS !!!
j++;
}
and printing (j is number of words actually read):
for (i = 0; i < j/*30*/; ++i) { // (!) how to print
printf("%s\n", stringArray[i]);
}
And, yes strtok would also do the job.
In words() you're assigning values to stringArray as a two-dimensional array, and in main() you're reading values from it as an array of pointers. Those are not the same thing.
So you need to change it so that you're consistently treating it as a 2D array, or so that you're consistently treating it as an array of pointers (char* to be exact). Either will work... see the comments above for elaboration.
This code is all wrong.
char** stringArray = (char**) malloc(sizeof(char)*30*30);
First of all, sizeof(char) is always one, second, you don't need to cast a void. So:
char **stringArray = malloc(30 * 30);
But that doesn't make any sense because it's an array of char *, so you should allocate in terms of that:
char **stringArray = malloc(sizeof(char *) * 30);
Or even better:
char **stringArray = malloc(sizeof(*stringArray) * 30);
So now you have an array with 30 char *, but each of those is not initialized, so you need to do that:
for (i = 0; i < 30; i++)
stringArray[i] = malloc(sizeof(**stringArray) * 30);
If you don't do that, you can't access stringArray[count][k].
And then you assume the last element in the array is NULL, but you never set it, so you either do stringArray[count] = NULL at the end of words(), or you do calloc() instead of malloc().
I'm not analyzing the code beyond that; it's just all wrong.
I'm parsing a text file:
Hello, this is a text file.
and creating by turning the file into a char[]. Now I want to take the array, iterate through it, and create an array of arrays that splits the file into words:
string[0] = Hello
string[1] = this
string[2] = is
This is my code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "TextReader.h"
#include <ctype.h>
void printWord(char *string) {
int i;
for (i = 0; i < strlen(string); i ++)
printf("%c", string[i]);
printf("\n");
}
void getWord(char *string) {
char sentences[5][4];
int i;
int letter_counter = 0;
int word_counter = 0;
for (i = 0; i < strlen(string); i ++) {
// Checks if the character is a letter
if (isalpha(string[i])) {
sentences[word_counter][letter_counter] = string[i];
letter_counter++;
} else {
sentences[word_counter][letter_counter + 1] = '\0';
word_counter++;
letter_counter = 0;
}
}
// This is the code to see what it returns:
i = 0;
for (i; i < 5; i ++) {
int a = 0;
for (a; a < 4; a++) {
printf("%c", sentences[i][a]);
}
printf("\n");
}
}
int main() {
// This just returns the character array. No errors or problems here.
char *string = readFile("test.txt");
getWord(string);
return 0;
}
This is what it returns:
Hell
o
this
is
a) w
I suspect this has something to do with pointers and stuff. I come from a strong Java background so I'm still getting used to C.
With sentences[5][4] you're limiting the number of sentences to 5 and the length of each word to 4. You'll need to make it bigger in order to process more and longer words. Try sentences[10][10]. You're also not checking if your input words aren't longer than what sentences can handle. With bigger inputs this can lead to heap-overflows & acces violations, remember that C does not check your pointers for you!
Of course, if you're going to use this method for bigger files with bigger words you'll need to make it bigger or allocate it dymanically.
sample that do not use strtok:
void getWord(char *string){
char buff[32];
int letter_counter = 0;
int word_counter = 0;
int i=0;
char ch;
while(!isalpha(string[i]))++i;//skip
while(ch=string[i]){
if(isalpha(ch)){
buff[letter_counter++] = ch;
++i;
} else {
buff[letter_counter] = '\0';
printf("string[%d] = %s\n", word_counter++, buff);//copy to dynamic allocate array
letter_counter = 0;
while(string[++i] && !isalpha(string[i]));//skip
}
}
}
use strtok version:
void getWord(const char *string){
char buff[1024];//Unnecessary if possible change
char *p;
int word_counter = 0;
strcpy(buff, string);
for(p=buff;NULL!=(p=strtok(p, " ,."));p=NULL){//delimiter != (not isaplha(ch))
printf("string[%d] = %s\n", word_counter++, p);//copy to dynamic allocate array
}
}