#include <stdio.h>
#include <string.h>
void mergeStr(char *a, char *b, char *c);
int main()
{
char a[80],b[80];
char c[80];
printf("Enter the first string: \n");
gets(a);
printf("Enter the second string: \n");
gets(b);
mergeStr(a,b,c);
printf("mergeStr(): ");
puts(c);
return 0;
}
void mergeStr(char *a, char *b, char *c)
{
int size; int i ; int j=0 ; // again, forgot to initialize j
char ch;
char temp[80] ;
/* Merge string a and string b together, then sort them alphabetically */
c = strcat(a,b) ;
size = strlen(c) ;
for (ch = 'A' ; ch <= 'z' ; ch++ ) { // iterates from A-Z and a-z
for (i=0 ; i<size ; i++) { // which for loop comes first is important, in this case since we want duplicates we should allow i to iterate everything for every case of ch
if (c[i] == ch){
temp[j] = c[i] ;
j++ ;
}
}
}
for (i=0 ; i<size ; i++) {
c[i] = temp[i] ; // assign sorted string back to c
c[size] = '\0' ;
}
// puts(c) <- when puts() is run here, desired output is given
}
In this program, the function takes char a , concatenates it with char b, which is assigned to c.
char c is then sorted and printed out in the main function by puts(c).
For example,
Enter the first string:
afkm
Enter the second string:
bbbggg
abbbfgggkm
mergeStr():
This is the output i get when puts(c) is run from within void mergeStr() function.
However, puts(c) from int main() does not print anything.
This:
/* Merge string a and string b together, then sort them alphabetically */
c = strcat(a,b) ;
doesn't do what you seem to expect, it doesn't write into the caller's (i.e. main()'s) buffer at all. It overwrites the value of c (the function argument) with the return value of strcat(), which will be the destination, i.e. a.
You need to read up on how C strings work, and how the memory holding them is handled.
That particular call could be replaced by:
sprintf(c, "%s%s", a, b);
but this is dangerous and risks overwriting buffers since no size information is passed into the function (so it can't use snprintf()).
Related
Basically the program is supposed to allow me to test the words . I am trying learn how to add multiple functions inside the main function but for some reason , I couldn't run the program . Could I know where is my mistake or how can I work on the program .
#include <stdio.h>
#include <ctype.h>
#include <stdbool.h>
void read_word(int counts[26]);
bool equal_array(int counts1[26] , int counts2[26]);
int main (void)
{
int counts1[26] = {0} , counts2[26] = {0} ;
read_word(counts1);
read_word(counts2);
if(equal_array(counts1, counts2)){
printf("The words are not anagrams");
}
else{
printf("The words are anagrams");
}
return 0;
}
void read_word(int counts[26])
{
char ch , alphabet ;
printf("Enter word: ");
//initialise the letters array first and assign all of them value of 0
for(alphabet = 'a' ; alphabet <= 'z'; alphabet++){
counts[alphabet] = 0;
}
//first loop to get the word and num
while ((ch = getchar()) != '\n')
{
if (isalpha(ch))
{
counts[tolower(ch)]++;
}
counts[ch]++; //Is this statement needed ? why ?
}
}
bool equal_array(int counts1[26] , int counts2[26])
{
char alphabet;
//third loop to check the whole array
for (alphabet = 'a' ; alphabet <= 'z'; alphabet++)
{
if (counts1[alphabet] != counts2[alphabet])
{
return true ;
}
else
{
return false;
}
}
}
As mentioned above in the comment, the ASCII value for 'a' is 97 and 122 for 'z'. When you attempt to iterate:
for(alphabet = 'a' ; alphabet <= 'z'; alphabet++){
counts[alphabet] = 0;
}
You access elements well beyond the end of your array -- invoking Undefined Behavior. See ASCII Table & Description. The irony (as also mentioned in the comment) is the loop is entirely unnecessary because your declaration and initialization of your arrays already set each element in the arrays to zero:
int counts1[26] = {0} , counts2[26] = {0};
While not an error, passing the arrays as, e.g. void read_word(int counts[26]);, shows a misconception of how arrays are treated on access. On access, an array is converted to a pointer to its first elements. This is known as Array / Pointer Conversion and it is set forth in the standard at C11 Standard - 6.3.2.1 Other Operands - Lvalues, arrays, and function designators(p3). What this means is you simply need to provide a pointer as the parameter to represent your arrays in the function arguments, e.g.
void read_word (int *counts);
bool equal_array (int *counts1, int *counts2);
Don't Hardcode Filenames or Use Magic Numbers in Your Code
When you write code, you don't want to sprinkle Magic Numbers (e.g. 26) or hardcode filenames. Instead, if you need a constant, #define one or use a global enum for the same purpose:
#include <stdio.h>
#include <ctype.h>
#include <stdbool.h>
#define ALPHA 26 /* if you need a constant, #define one (or more) */
...
int main (void)
{
int counts1[ALPHA] = {0},
counts2[ALPHA] = {0};
Why? If you need to make changes later to the value, you don't have to go picking through each array declaration or loop limit to make changes. You have one single convenient location up top to make the change and it is automatically applied throughout your code.
If you need to pass a filename to your program, pass it as an argument to main() (that's what int argc, char **argv are for) or take input from the user. Why? You shouldn't have to recompile your program just to read from a different filename.
Match Your Variable Type to Function Return Type
Declaring char ch; and then assigning ch = getchar(); is not right. Why? What is the declaration for getchar()? See man 3 getchar. How is it declared and what does it return?
int getchar(void);
The function returns int not char, so you must declare int ch; instead of char ch;. It also allows you to validly check if (ch == EOF).
Your read_word() Function
When you are reading with getchar(), in addition to checking for '\n', you must also check for EOF. There is no guarantee your line will end with '\n'. The user may very well generate a manual EOF with Ctrl + d (or Ctrl + z on windows). Therefore your loop should be:
void read_word (int *counts)
{
int ch; /* ch must be int to match getchar() and catch EOF */
fputs ("Enter word: ", stdout);
while ((ch = getchar()) != '\n' && ch != EOF) /* loop over each char in line */
{
if (isalpha(ch))
{
counts[tolower(ch) - 'a']++; /* map to zero-based index */
}
// counts[ch]++; //Is this statement needed ? why ?
// no - only alpha chars are counted
}
}
Note: tolower() returns lower-case character (e.g. the ASCII value for the lower-case character). Therefore to map the character back to your Zero-Based array index, you must subtract 'a' from the return.
Give Your Functions Names With Plain Meaning
Your equal_array() function returns true if the arrays counts1 and counts2 are NOT equal and returns false if the ARE equal. That is directly opposite of what equal_arrays means. Instead, you could do:
bool equal_array (int *counts1, int *counts2)
{
for (int i = 0; i < ALPHA; i++)
if (counts1[i] != counts2[i])
return false;
return true;
}
(note: there is never the need for an else if all that happens is a return)
Putting it altogether you would have:
#include <stdio.h>
#include <ctype.h>
#include <stdbool.h>
#define ALPHA 26 /* if you need a constant, #define one (or more) */
void read_word (int *counts);
bool equal_array (int *counts1, int *counts2);
int main (void)
{
int counts1[ALPHA] = {0},
counts2[ALPHA] = {0};
read_word(counts1);
read_word(counts2);
if (equal_array(counts1, counts2))
puts ("The words are anagrams");
else
puts ("The words are not anagrams");
return 0;
}
void read_word (int *counts)
{
int ch; /* ch must be int to match getchar() and catch EOF */
fputs ("Enter word: ", stdout);
while ((ch = getchar()) != '\n' && ch != EOF) /* loop over each char in line */
{
if (isalpha(ch))
{
counts[tolower(ch) - 'a']++; /* map to zero-based index */
}
// counts[ch]++; //Is this statement needed ? why ?
// no - only alpha chars are counted
}
}
bool equal_array (int *counts1, int *counts2)
{
for (int i = 0; i < ALPHA; i++)
if (counts1[i] != counts2[i])
return false;
return true;
}
Example Use/Output
$ ./bin/isanagram
Enter word: anagram
Enter word: nag a ram
The words are anagrams
or
$ ./bin/isanagram
Enter word: anagram
Enter word: nag a ham
The words are not anagrams
Now it is working as it should. Let me know if you have any further questions.
I have been trying to reverse(and print it that way) a given string only using for loops and nothing more. I think I have built up the basic logic, but it has some defects. When run, it only reverses the first two characters and then stops. Please help me find the defect in my logic.
#include<stdio.h>
#include<stdlib.h>
int main()
{
char a[20];
int i;
printf("Enter any String\n");
gets(a);
for(i=0;a[i]!=NULL;i++)
{}
for(i=1;i>=0;i--)
{
printf("%c",a[i]);
}
}
For starters the function gets is not a standard C function any more. it is unsafe. Instead use the standard C function fgets. The function can append the new line character '\n' to the entered string that should be excluded from the string.
It is unclear from your question whether you are allowed to use standard string functions.
Nevertheless here is a demonstrative program that does the task without using standard C string functions and that uses only for loops (neither while loop nor do-while loop).
#include <stdio.h>
int main(void)
{
enum { N = 20 };
char s[N];
printf( "Enter any String less than %d symbols: ", N );
fgets( s, N, stdin );
// remove the new line character and calculate the length of the string
size_t n = 0;
for ( ; s[n] != '\0' && s[n] != '\n'; ) ++n;
s[n] = '\0';
// reverse the string
for ( size_t i = 0; i < n / 2; i++ )
{
char c = s[i];
s[i] = s[n-i-1];
s[n-i-1] = c;
}
puts( s );
return 0;
}
Its output might look the following way
Enter any String less than 20 symbols: Hello dev.aniruddha
ahddurina.ved olleH
If you want just to output the original string in the reverse order then the program can look like
#include <stdio.h>
int main(void)
{
enum { N = 20 };
char s[N];
printf( "Enter any String less than %d symbols: ", N );
fgets( s, N, stdin );
// remove the new line character and calculate the length of the string
size_t n = 0;
for ( ; s[n] != '\0' && s[n] != '\n'; ) ++n;
s[n] = '\0';
// reverse the string
for ( ; n-- != 0; )
{
putchar( s[n] );
}
putchar( '\n' );
return 0;
}
Its output is the same as shown above
Enter any String less than 20 symbols: Hello dev.aniruddha
ahddurina.ved olleH
gets() is a bad idea as you can easily get overflows and it is no longer part of the c standard.
So let's assume that the string entered fits the array and this is just for an excercise with no reallife usage.
Your first loop finds the terminator. That's good.
Your second loop sets the variable that indicates the terminator to 1, destroying the result.
If you remove the assignment i=1, your program compiles with gcc and does what you want.
#include<stdio.h>
#include<stdlib.h>
int main()
{
char a[20];
int i;
printf("Enter any String\n");
gets(a);
for(i=0;a[i]!=NULL;i++)
{}
for(;i>=0;i--) //removed i=1 here
{
printf("%c",a[i]);
}
}
But there are still some issues to be addressed.
You will also reverse the terminator, instead you should start from i-1
I would advise to not use a for loop if you do not have a counter criterion The first loop should rather be a while loop, but as it was part of the assignment you had no choice still I will replace it in my recommendation. As they can easily be swapped.
Then you could use another variable for the second loop for clarity.
Also NULL is the NULL-pointer not the value 0 (also namend NUL apperantly) . So you should replace this either with 0 or with '\0'
Also stdlib.h is not required here
#include<stdio.h>
int main()
{
char a[20];
int i = 0;
printf("Enter any String\n");
gets(a);
while (a[i] != 0)
{
i++;
}
for(int j = i-1; j>=0; j--) // -1 to get the value in front of the terminator
{
printf("%c",a[j]);
}
printf("\n"); //to flush the output.
}
Here is the solution code.
The first for loop is to be used for determining the length of the string and the second for loop is for traversing the string from the last position to the first.
#include<stdio.h>
int main()
{
char a[20];
int i,j,len;
printf("Enter a String\n");
gets(a);
for(i=0;a[i]!=NULL;i++)
{}
len=i;
for(j=len-1;j>=0;j--)
{
printf("%c",a[j]);
}
}
I think why only two chars are been return is because of the condition statement in your second "for loop".
for(i=1;i>=0;i--)
Note:
it repeats from 1~0 (1,0): meaning it will repeat only twice
first iteration: when i == 1
second iteration: when i == 0 ; then it ends .
Please note that you created two "for loops" with the first one having no content.
Bonus:
I tried to fixed your code but realized that my C language skills isnt the best lol . Anyways, i came up with something that you could reference but it only reverse strings of less than 8 elements.
#include<stdio.h>
#include<stdlib.h>
int findlength(char a[]);
int main()
{
char a[20];
int i;
printf("Enter any String\n");
gets(a);
int len = findlength(a);
printf("Lenght of the String is: %d \n",len);
printf("Reversed String is: ");
for(i=len;i>-1;i--){
printf("%c",a[i]);
}
}
int findlength(char a[]){
int result = 0;
int i;
for(i=0;i<sizeof(a) / sizeof(char);i++){ // sizeof(char) is 1
if(a[i] == '\0') //end of string
return result;
result += 1;
}
return result;
}
I'm relatively new to coding array functions in C. After numerous tries, I've decided to surrender and ask for help.
I wish to the user to input the words and store them into the 2d array words. The problem is that it prints the words but also prints out random characters.
#include "mp1_lib.h"
void get_words(int n, char words[][16])
{
char c = ' ';
char check;
for(int x=0; x <= n; x++)
{
for(int y=0; y < 16; y++)
{
c = getchar();
check = c;
if (check == '\n')
{
break;
}
words[x][y] = c;
}
}
}
void print_words(int n, char words[][16])
{
for(int x=1; x <= n; x++)
{
for(int y=0; y < 16; y++)
{
if (words[x][y] == '\n')
{
break;
}
putchar(words[x][y]);
}
printf("\n");
}
}
In C, a string is an array of characters with the nul-terminating character '\0' as the character that marks the end of the contents of the string within the array. That is how all string functions like strlen or printf using the '%s' format specifier to print a string -- know where the string stops.
If you do not nul-terminate the array of characters -- then it is not a string, it is simply an array and you cannot pass an un-terminate array to any function expecting a string - or it won't know where the string ends (and in the case of printf will just print whatever unspecified character happens to be in memory until it comes upon a '\0' to stop the output (or SegFaults).
If you don't nul-terminate the words in your array, then you will have to have some way to store the number of characters in each word, so your print function will know where to stop printing. (if you have a two-letter word like "Hi" in a 16-char array, you can only print 2 characters from the array. Especially if it is an uninitialized array, then you will simply get gibberish printed for characters 3-16.
Your second problem is -- "How do you know how many words you have stored in your array?" -- you don't return a value from getwords, so unless you change the function type to int and return the number of words that you stored in your array, your only other option is to pass a pointer to an integer and update the value at that address so the value is available back in the calling function. Either way is fine, you generally only worry about making a value available through a pointer if you are already returning another value and need a second method to make another updated value visible back in the calling function (main() here).
Putting those pieces together, and passing a pointer to the number of words to getwords to make the number of words entered available back in main() (so you know how many words print_words has to print), you could do something similar to the following:
#include <stdio.h>
#include <ctype.h>
#define MAXC 16 /* if you need constants, define them */
#define MAXW 32
void getwords (char (*words)[MAXC], int *n)
{
int col = 0; /* column count */
while (*n < MAXW) { /* while words < MAXW */
int c = getchar(); /* read char */
/* column reaches MAXC-1 or if whitespace or EOF */
if (col == MAXC - 1 || isspace(c) || c == EOF) {
if (col) { /* if col > 0 */
words[(*n)++][col] = 0; /* nul-terminate, increment n */
col = 0; /* set col to zero */
}
if (c == EOF) /* if char EOF - all done */
return;
}
else /* otherwise - just add char to word */
words[*n][col++] = c;
}
}
void prnwords (char (*words)[MAXC], int n)
{
for (int i = 0; i < n; i++) /* loop over each of n-words & print */
printf ("words[%2d]: %s\n", i, words[i]);
}
int main (void) {
char words[MAXW][MAXC] = {""}; /* intiliaze words all zero */
int nwords = 0; /* number of words zero */
getwords (words, &nwords);
prnwords (words, nwords);
return 0;
}
(note: when reading characters into the words array, you must check the number of character read again the maximum characters per-word (MAXC) and the number of words against the maximum number of words/rows in your array (MAXW) to prevent writing outside of your array bounds -- which will invoke Undefined Behavior in your program)
(note: the ctype.h header was included to simplify checking whether the character read was whitespace (e.g. a space, tab, or newline). If you can't use it, then simply use an if (c == ' ' || c == '\t' || c == '\n') instead.)
Example Use/Output
$ echo "my dog has fleas and my cat has none" | ./bin/getwords
words[ 0]: my
words[ 1]: dog
words[ 2]: has
words[ 3]: fleas
words[ 4]: and
words[ 5]: my
words[ 6]: cat
words[ 7]: has
words[ 8]: none
Not too familiar with c. But it appears like you are not addding the new line character to the words array in get_words.
check = c;
if (check == '\n')
{
break;
}
words[x][y] = c;
So when printing in print_words this will never be true.
if (words[x][y] == '\n')
{
break;
}
That means that whatever happens to be in the memory location is what will get printed.
Your words have neither the newline character (which makes your code print garbage) nor the terminating NULLs (which makes them illegal as C strings). At least add words[x][y]="\n" before breaking the inner loop. Or, rather, move the if check after the assignment words[x][y]=c;. And yes, the loop should go from 0 to n-1.
As a side note, you do not need the variable check: just use c.
I tried to assign space as a placeholder for the 15 characters and it worked. Thanks, everyone! :)
#include "mp1_lib.h"
void get_words(int n, char words[][16])
{
char c = ' ';
char check;
for(int x=0; x < n; x++)
{
for(int y=0; y < 16; y++)
{
words[x][y] = ' ';
}
}
for(int x=0; x < n; x++)
{
for(int y=0; y < 16; y++)
{
c = getchar();
check = c;
if (check == '\n')
{
break;
}
words[x][y] = c;
}
}
}
void print_words(int n, char words[][16])
{
for(int x=0; x < n; x++)
{
for(int y=0; y < 16; y++)
{
putchar(words[x][y]);
}
printf("\n");
}
}
I have the following program that I want to read in my name (Sahand) character by character and store in a string:
#include <stdio.h>
int main(int argc, const char * argv[]) {
char temp;
char str[6];
int i;
for ( i = 0 ; i < 6 ; i++ )
{
scanf(" %c",&temp);
printf("Our temp is: %c\n",temp);
str[i] = temp;
printf("Our total string is: %s\n",str);
}
printf("Program ended with the string: %s\n",str);
return 0;
}
The output is this:
s
Our temp is: s
Our total string is: s
a
Our temp is: a
Our total string is: sa
h
Our temp is: h
Our total string is: sah
a
Our temp is: a
Our total string is: saha
n
Our temp is: n
Our total string is: sahan
d
Our temp is: d
Our total string is: sahandd\350\367\277_\377
Program ended with the string: sahandd\350\367\277_\377
Program ended with exit code: 0
As you can see, everything is going fine until the final letter, d, is entered, when another d and a bunch of random stuff is added onto the string. Could someone explain to me what is happening here?
You should be adding the null character to the string before printing. Since you're printing inside a loop, add it to the next character. Just absolutely be sure that the for loop doesn't go beyond the bounds of the array.
#include <stdio.h>
int main(int argc, const char * argv[]) {
char temp;
char str[7];
int i;
for ( i = 0 ; i < 6 ; i++ )
{
scanf(" %c",&temp);
printf("Our temp is: %c\n",temp);
str[i] = temp;
str[i+1] = '\0';
printf("Our total string is: %s\n",str);
}
printf("Program ended with the string: %s\n",str);
return 0;
}
Another option is to actually initialize each character in the C-String to be the '\0' character (without ever overwriting the last one); As some others have mentioned in the comments, this can be accomplished in the declaration of the array as such:
char str[7] = { 0 };
You need null character('\0') to end your string(array) at the 5th index in order to tell the compiler that this is the end of string(in your case character array i.e., str). But you were using 5th index to store character 'd'.
The compiler is taking garbage value from the memory
In order to run your program correctly, you need to declare the str array as below:
char str[7];
And insert null character('\0') at (i+1)th position.Look below:
#include <stdio.h>
int main(int argc, const char * argv[]) {
char temp;
char str[7];
int i;
for ( i = 0 ; i < 6 ; i++ )
{
scanf(" %c",&temp);
printf("Our temp is: %c\n",temp);
str[i] = temp;
str[i+1] = '\0';
printf("Our total string is: %s\n",str);
}
printf("Program ended with the string: %s\n",str);
return 0;
}
After reading the comments, I changed the following line in my program:
char str[6];
to
char str[7];
That did the trick and the program executes as I wish.
EDIT:
In addition to changing this line, I added a str[6] = 0; after the variable declaration.
I am writing C program that reads input from the standard input a line of characters.Then output the line of characters in reverse order.
it doesn't print reversed array, instead it prints the regular array.
Can anyone help me?
What am I doing wrong?
main()
{
int count;
int MAX_SIZE = 20;
char c;
char arr[MAX_SIZE];
char revArr[MAX_SIZE];
while(c != EOF)
{
count = 0;
c = getchar();
arr[count++] = c;
getReverse(revArr, arr);
printf("%s", revArr);
if (c == '\n')
{
printf("\n");
count = 0;
}
}
}
void getReverse(char dest[], char src[])
{
int i, j, n = sizeof(src);
for (i = n - 1, j = 0; i >= 0; i--)
{
j = 0;
dest[j] = src[i];
j++;
}
}
You have quite a few problems in there. The first is that there is no prototype in scope for getReverse() when you use it in main(). You should either provide a prototype or just move getReverse() to above main() so that main() knows about it.
The second is the fact that you're trying to reverse the string after every character being entered, and that your input method is not quite right (it checks an indeterminate c before ever getting a character). It would be better as something like this:
count = 0;
c = getchar();
while (c != EOF) {
arr[count++] = c;
c = getchar();
}
arr[count] = '\0';
That will get you a proper C string albeit one with a newline on the end, and even possibly a multi-line string, which doesn't match your specs ("reads input from the standard input a line of characters"). If you want a newline or file-end to terminate input, you can use this instead:
count = 0;
c = getchar();
while ((c != '\n') && (c != EOF)) {
arr[count++] = c;
c = getchar();
}
arr[count] = '\0';
And, on top of that, c should actually be an int, not a char, because it has to be able to store every possible character plus the EOF marker.
Your getReverse() function also has problems, mainly due to the fact it's not putting an end-string marker at the end of the array but also because it uses the wrong size (sizeof rather than strlen) and because it appears to re-initialise j every time through the loop. In any case, it can be greatly simplified:
void getReverse (char *dest, char *src) {
int i = strlen(src) - 1, j = 0;
while (i >= 0) {
dest[j] = src[i];
j++;
i--;
}
dest[j] = '\0';
}
or, once you're a proficient coder:
void getReverse (char *dest, char *src) {
int i = strlen(src) - 1, j = 0;
while (i >= 0)
dest[j++] = src[i--];
dest[j] = '\0';
}
If you need a main program which gives you reversed characters for each line, you can do that with something like this:
int main (void) {
int count;
int MAX_SIZE = 20;
int c;
char arr[MAX_SIZE];
char revArr[MAX_SIZE];
c = getchar();
count = 0;
while(c != EOF) {
if (c != '\n') {
arr[count++] = c;
c = getchar();
continue;
}
arr[count] = '\0';
getReverse(revArr, arr);
printf("'%s' => '%s'\n", arr, revArr);
count = 0;
c = getchar();
}
return 0;
}
which, on a sample run, shows:
pax> ./testprog
hello
'hello' => 'olleh'
goodbye
'goodbye' => 'eybdoog'
a man a plan a canal panama
'a man a plan a canal panama' => 'amanap lanac a nalp a nam a'
Your 'count' variable goes to 0 every time the while loop runs.
Count is initialised to 0 everytime the loop is entered
you are sending the array with each character for reversal which is not a very bright thing to do but won't create problems. Rather, first store all the characters in the array and send it once to the getreverse function after the array is complete.
sizeof(src) will not give the number of characters. How about you send i after the loop was terminated in main as a parameter too. Ofcourse there are many ways and various function but since it seems like you are in the initial stages, you can try up strlen and other such functions.
you have initialised j to 0 in the for loop but again, specifying it INSIDE the loop will initialise the value everytime its run from the top hence j ends up not incrmenting. So remore the j=0 and i=0 from INSIDE the loop since you only need to get it initialised once.
check this out
#include <stdio.h>
#include <ctype.h>
void getReverse(char dest[], char src[], int count);
int main()
{
// *always* initialize variables
int count = 0;
const int MaxLen = 20; // max length string, leave upper case names for MACROS
const int MaxSize = MaxLen + 1; // add one for ending \0
int c = '\0';
char arr[MaxSize] = {0};
char revArr[MaxSize] = {0};
// first collect characters to be reversed
// note that input is buffered so user could enter more than MAX_SIZE
do
{
c = fgetc(stdin);
if ( c != EOF && (isalpha(c) || isdigit(c))) // only consider "proper" characters
{
arr[count++] = (char)c;
}
}
while(c != EOF && c != '\n' && count < MaxLen); // EOF or Newline or MaxLen
getReverse( revArr, arr, count );
printf("%s\n", revArr);
return 0;
}
void getReverse(char dest[], char src[], int count)
{
int i = count - 1;
int j = 0;
while ( i > -1 )
{
dest[j++] = src[i--];
}
}
Dealing with strings is a rich source of bugs in C, because even simple operations like copying and modifying require thinking about issues of allocation and storage. This problem though can be simplified considerably by thinking of the input and output not as strings but as streams of characters, and relying on recursion and local storage to handle all allocation.
The following is a complete program that will read one line of standard input and print its reverse to standard output, with the length of the input limited only by the growth of the stack:
int florb (int c) { return c == '\n' ? c : putchar(florb(getchar())), c; }
main() { florb('-'); }
..or check this
#include <stdio.h>
#include <stdlib.h>
#define MAX 100
char *my_rev(const char *source);
int main(void)
{
char *stringA;
stringA = malloc(MAX); /* memory allocation for 100 characters */
if(stringA == NULL) /* if malloc returns NULL error msg is printed and program exits */
{
fprintf(stdout, "Out of memory error\n");
exit(1);
}
else
{
fprintf(stdout, "Type a string:\n");
fgets(stringA, MAX, stdin);
my_rev(stringA);
}
return 0;
}
char *my_rev(const char *source) /* const makes sure that function does not modify the value pointed to by source pointer */
{
int len = 0; /* first function calculates the length of the string */
while(*source != '\n') /* fgets preserves terminating newline, that's why \n is used instead of \0 */
{
len++;
*source++;
}
len--; /* length calculation includes newline, so length is subtracted by one */
*source--; /* pointer moved to point to last character instead of \n */
int b;
for(b = len; b >= 0; b--) /* for loop prints string in reverse order */
{
fprintf(stdout, "%c", *source);
len--;
*source--;
}
return;
}
Output looks like this:
Type a string:
writing about C programming
gnimmargorp C tuoba gnitirw