Strings in C Language - c

How can you code this in C language if the output is like this? I need strings format of the code because our topic is strings.
#include <stdio.h>
#include <stdlib.h>
void main()
{
char my_string[50];
printf("Enter a word:");
scanf("%s", my_string);
printf("Enter a word:");
scanf("%s", my_string);
// Some unknown code here...
// this part is my only problem to solve this.
getch();
}
Output:
Hello -> (user input)
World -> (user input)
HWeolrllod -> (result)

Okay, you need to do some investigating. We don't, as a general rule, do people's homework for them since:
it's cheating.
you'll probably get caught out if you copy verbatim.
it won't help you in the long run at all.
The C library call for user input that you should use is fgets, along the line of:
char buffer[100];
fgets (buffer, sizeof(buffer), stdin);
This will input a string into the character array called buffer.
If you do that with two different buffers, you'll have the strings in memory.
Then you need to create pointers to them and walk through the two strings outputting alternating characters. Pointers are not an easy subject but the following pseudo-code may help:
set p1 to address of first character in string s1
set p1 to address of first character in string s1
while contents of p1 are not end of string marker:
output contents of p1
add 1 to p1 (move to next character)
if contents of p2 are not end of string marker:
output contents of p2
add 1 to p2 (move to next character)
while contents of p2 are not end of string marker:
output contents of p2
add 1 to p2 (move to next character)
Translating that into C will take some work but the algorithm is solid. You just need to be aware that a character pointer can be defined with char *p1;, getting the contents of it is done with *p1 and advancing it is p = p + 1; or p1++;.
Short of writing the code for you (which I'm not going to do), there's probably not much else you need.

void main()
{
char my_string1[50],my_string2[50]; int ptr;
ptr=0;
printf("Enter a word : ");
scanf("%s",my_string1);
printf("enter a word");
scanf("%s",my_string2);
while(my_string1[ptr]!='\0' && my_string2[ptr]!='\0')
{
printf("%c%c",my_string1[ptr],my_string2[ptr]);
ptr++;
}
if(my_string1[ptr]!='\0')
{
while(my_string1[ptr]!='\0')
{ printf("%c",my_string1[ptr]);
ptr++;
}
}
else
{
while(my_string2[ptr]!='\0')
{printf("%c",my_string2[ptr]);
ptr++;
}
}
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void main()
{
char my_string1[50],my_string2[50];
int i,l1=1,l2=0;
printf("Enter a word:");
scanf("%s", my_string1);
printf("Enter a word:");
scanf("%s", my_string2);
l1=strlen(my_string1); /* Length of 1st string */
l2=strlen(my_string2); /* Length of 2nd string */
if(l1==l2)
{
for(i=0;i<l1;i++)
{
printf("%c%c",my_string1[i],my_string2[i]);
}
}
else
{
printf("Length of the entered strings do not match");
}
}
This is your required code.

You can see that output needs to be a String containing all chars of User String1 and User String2 one by one...
You can do this like...
//add #include<String.h>
int l1=strlen(s1);
int l2=strlen(s2);
if(l1!=l2)
{
printf("length do not match");
return 0;
}
char ansstr[l1+l2];
int i,j=0,k=0;
for(i=0;i<l1+l2;i=i+2)
{
ansstr[i]=s1[j];
ansstr[i+1]=s2[k];
j++;
k++;``
}
//ansstr is your answer

Ok, here's your code. Come on guys, if he asked here it means he can't solve this.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv[])
{
char str1[] = "abcdefghijklmopq";
char str2[] = "jklm";
int len1 = strlen(str1);
int len2 = strlen(str2);
int c1 = 0, c2 = 0;
int max = (len1 > len2) ? len1 : len2 ;
char *result = malloc(len1 + len2);
for(c1 = 0; c1 <= max; c1++) {
if(c1 < len1)
result[c2++] = str1[c1];
if(c1 < len2)
result[c2++] = str2[c1];
}
result[c2] = 0;
printf("\n%s\n", result);
return 0;
}
Basically the loop picks up a character from str1 and appends it to result. Then it picks a character, which stands in the same position as the first from str2 and appends it to result, just as before. I increment c2 by 2 every time because I'm adding 2 chars to result. I check if c1 is bigger that the length of the strings because I want to copy only the characters in the string without the terminating \0. If you know that your strings have the same length you can omit these ifs.

Related

Appending chars into a String in C with a for loop

I'm still a newbie to C so please forgive me if anything below is wrong. I've searched this up online but nothing really helped.
Right now, I have the following code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void appendStr (char *str, char c)
{
for (;*str;str++); // note the terminating semicolon here.
*str++ = c;
*str++ = 0;
}
int main(){
char string[] = "imtryingmybest";
char result[] = "";
for(int i = 0; i < strlen(string); i++){
if(i >= 0 && i <= 3){
appendStr(result, string[i]);
}
}
printf("%s", result);
}
Basically, I'm trying to add the first 4 characters of the String named string to result with a for loop. My code above did not work. I've already tried to use strcat and strncat and neither of them worked for me either. When I used
strcat(result, string[i]);
It returns an error saying that the memory cannot be read.
I know that in this example it might have been easier if I just did
appendStr(result, string[0]);
appendStr(result, string[1]);
appendStr(result, string[2]);
appendStr(result, string[3]);
But there is a reason behind why I'm using a for loop that couldn't be explained in this example.
All in all, I'd appreciate it if someone could explain to me how to append individual characters to a string in a for loop.
The following code doesnt use your methods but successfully appends the first 4 chars to result
#include <stdio.h>
#include <string.h>
int main()
{
// declare and initialize strings
char str[] = "imtryingmybest";
char result[5]; // the 5th slot is for \0 as all strings are null terminated
// append chars to result
strncat(result, str, 4);
// ^ ^ ^
// | | |- number of chars to be appended
// | | - string to be appended from
// | - string to append to
// print string
printf("result: %s\n", result);
return (0);
}
The result of the above is as wanted:
>> gcc -o test test.c
>> ./test
result: imtr
Let me know if anything is not clear so i can elaborate further
string was ruined by the overflow of result buffer.
appendStr can be executed only once. next time strlen(string) will return 0. because *str++ = 0; has been written to the space of string.
result buffer has only 1 byte space, but you write 2 byte to it in appendStr call.
the second byte will ruin string space.
I suggest debug with gdb.
try to get rid of Magic numbers
#define BUFF_SIZE 10 // define some bytes to allocate in result char array
#define COPY_COUNT 4 // count of chars that will be copied
int main(){
char string[] = "imtryingmybest";
char result[BUFF_SIZE] {}; // allocate some chunk of memory
for(size_t i = 0; i < strlen(string); i++){
if(i < COPY_COUNT){
appendStr(result, string[i]);
}
}
printf("%s", result);
}
I showed the solution code Paul Yang showed the problem
As others have pointed out the code has a simple mistake in the allocation of the destination string.
When declaring an array without specifying its size, the compiler deduces it by its initializer, which in your case means a 0 + the NULL character.
char result[] = ""; // means { '\0' };
However, I think that the bigger issue here is that you're effectively coding a Schlemiel.
C strings have the serious drawback that they don't store their length, making functions that have to reach the end of the string linear in time complexity O(n).
You already know this, as shown by your function appendStr()
This isn't a serious issue until start you appending characters or strings in a loop.
In each iteration of your loop appendStr() reaches the last character of the string, and extends the string, making the next iteration a little slower.
In fact its time complexity is O(n²)
Of course this is not noticeable for small strings or loops with few iterations, but it'll become a problem if the data scales.
To avoid this you have to take into account the growing size of the string.
I modified appendStr() to show that now it starts from the last element of result
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void appendStr (char *str, char c, char *orig)
{
printf("i: %ld\n", str - orig);
for (; *str; str++); // note the terminating semicolon here.
*str++ = c;
*str++ = 0;
}
int main()
{
char string[32] = "imtryingmybest";
char result[32] = "";
for(int i = 0; i < strlen(string); i++) {
if(i >= 0 && i <= 3) {
// I'm passing a pointer to the last element of the string
appendStr(&result[i], string[i], result);
}
}
printf("%s", result);
}
You can run it here https://onlinegdb.com/HkogMxbG_
More on Schlemiel the painter
https://www.joelonsoftware.com/2001/12/11/back-to-basics/
https://codepen.io/JoshuaVB/pen/JzRoyp

If i input too many characters my program either has a 'mremap_chunk(): invalid pointer' or a 'realloc(): invalid old size'

my program was built as a test to input as many sentences as the user want (until he enters -1), and then concatenate all sentences (\n included). If i input some characters is fine, but if i input more then 25 characters i have the two errors listed above, i tried simulating what would happen in paper and i can´t find the problem, help is appreciated, thanks in advance.
The code is displayed below:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
char *s = malloc(1), *sentence = malloc(0);
int sSize = 0;
printf("Insert sentences, press '-1' if you want to exit:\n");
do
{
fgets(s,100,stdin);
if(strcmp(s,"-1\n") != 0)
{
sSize += strlen(s);
sentence = realloc(sentence, sSize * sizeof(char));
//s[strcspn(s, "\0")] = '\n';
strcat(sentence, s);
}
}while(strcmp(s,"-1\n") != 0);
printf("==================sentence================\n");
printf("%s", sentence);
return 0;
}
This is a classic buffer overrun problem:
s = malloc(1) - s now points to a one-character buffer.
fgets(s,100,stdin); - reads up to 100 characters into s - which is a one-character buffer.
EDIT
Here's a version which works and doesn't use a separate "sentence buffer":
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(void)
{
const char *terminator = "-1\n";
char *sentences = malloc(100);
char *pNext_sentence;
printf("Insert sentences, press '-1' if you want to exit:\n");
*sentences = '\0';
do
{
sentences = realloc(sentences, strlen(sentences)+100);
pNext_sentence = sentences + strlen(sentences);
fgets(pNext_sentence, 100, stdin);
} while(strcmp(pNext_sentence, terminator) != 0);
*(sentences + (strlen(sentences) < strlen(terminator) ? 0 : strlen(sentences) - strlen(terminator))) = '\0';
printf("==================sentences================\n");
printf("%s", sentences);
free(sentences);
return 0;
}
You must use reallocate memory with realloc before using fgets, which, in your case, reads 100 bytes.
Your string has the initial size of 1.

Resize specific cells of array in c

#include <stdio.h>
#include <stdlib.h>
#include <stdio.h>
char *readline()
{
char s[256],*ds;
printf("Give string: ");
gets(s);
ds = (char *) calloc(strlen(s)+1,sizeof(char));
strcpy(ds,s);
return ds;
}
main()
{
char *s1,*s2;
int a,b;
s1=readline();
printf("Start:");
scanf("%d",&a);
printf("End:");
s2=(char*)realloc(s1,b-a);
puts(s2);
return 0;
}
I have this code and I want to resize specific cells of the s1 array which are determined from the variables a and b.
E.g. If I give the string "Hello" and the integers a=2 and b=4 then I want the program to print "ell".
Don't use gets use fgets instead.
With fgets you would use if( fgets( s,256, stdin)!= NULL ){ /*Got input in s*/ }.
You have taken \n as input also. s[strcspn(s,"\n")]=0 will overwrite \n with \0.
Casting return value of calloc is not needed since, void* will be implicitly converted to char*. calloc may return NULL - you didn't include check in there.
ds = calloc(strlen(s)+1,sizeof(char));
if( NULL == ds ){
perror("calloc: error");
exit(EXIT_FAILURE);
}
In main() value of b is indeterminate. You didn't take input in b.
if( scanf("%d",&b)!= 1){
fprintf(stderr,"Error in input");
exit(EXIT_FAILURE);
}
Then you realloc-ed. But not clear why. If you thought that shrinking the memory to 4-2 or 2 Bytes will help you get "ell" then you are wrong in many ways. It won't.
what you can do is - allocate memory for that in s2.
if(b<a){
fprintf(stderr,"End must be greater than beginnning\n");
exit(EXIT_FAILURE);
}
s2 = malloc(b-a+1);
if(!s2){
perror("calloc: error");
exit(EXIT_FAILURE);
}
memcpy(s2,s1+a,b-a);
s2[b-a]=0;
puts(s2);
This will print the relevant "ell" just you wanted. There is one thing left for you - put the code snippets in the code.
Since you are open to other solutions:
If there is another way then no problem.
I would point you to a simple solution, where you terminate the original string at b and skip required number of characters a. (Note: in C char array starts from index 0);
This is the idea:
#include <stdio.h>
#include <string.h>
char *splice(char *str, int s, int e)
{
str[e]=0;
return (str+s-1);
}
int main()
{
char *after;
int a=2;
int b=4;
char original[] = { 'H', 'e', 'l' , 'l' , 'o', 0 };
after = splice(original,a,b);
printf("My new string = %s", after);
return 0;
}
Output:
My new string = ell

Reversing a string in C using Visual Studio

I'm building a program for reversing a string in visual studio, and while I run the code and enter a word I want to reverse, the program crashes.
#include <stdio.h>
#include <conio.h>
#include <string.h>
main(void) {
char r[256];
int i, d;
printf("\nEnter the word you want to reverse : ");
gets_s(" %s", r, sizeof(r));
d = strlen(r);
for (i=d;i!=0;i--) {
printf("%s",i);
}
return 0;
}
Please note that I tried your program on Linux, so no MS Visual C++ and more specifically no conio.h and gets_s.
There are multiple problems with your program:
Your call to gets_s is incorrect, according to this and this, gets_s is defined as:
char *gets_s(
char *buffer,
size_t sizeInCharacters
);
You are calling it with illegal arguments. Instead of gets_s(" %s", r, sizeof(r)); you need to call it like this:
gets_s(r, 256);
the first parameter is pointer to the string buffer where the gets_s function will store the line from input and the second is the size of the buffer, note that in char r[256] you can store 255 characters and terminating zero (\0).
Your for loop is incorrect instead of for (i=d;i!=0;i--) { you need to do it like this:
for (i=d-1;i>=0;i--) {
now the loop starts from last character instead of \0 and ends when the i < 0 ie. the last print will be when i=0.
And your final mistake is that you are using printf incorrectly instead of printf("%s",i); you need to do:
printf("%c",r[i]);
because you are printing characters: "%c" is for char output and r[i] is i-th character from string r (don't forget that we count from 0).
So, in total this is how the program should look like:
#include <stdio.h>
#include <conio.h> // does not exist on GCC (Linux)
#include <string.h>
main(void) {
char r[256]; // 255 characters + \0
int i, d;
printf("\nEnter the word you want to reverse : ");
gets_s(r, 256); // store at most 255 characters + \0
// does not work on GCC (Linux) even with -std=C11
d = strlen(r);
// start from last character and include first
for (i=d-1;i>=0;i--) {
// %c - character, r[i] gets the i-th character from string r
printf("%c",r[i]);
}
return 0;
}
void rev(char *s)
{
char *start, *end;
end = start + strlen(s) - 1;
for (start = s; end > start; ++start, --end) {
char tmp;
tmp = *start;
*start = *end;
*end = tmp;
}
}
Use the fgets function, and also put the reversing code in its own function, like I did. So the final code is
int main()
{
char line[80];
fgets(line, 80, stdin);
/* don't allow empty string */
if (*line == '\0') {
fprintf(stderr, "Empty string is not a string\n");
return 1;
}
/* remove the \n placed by fgets */
remnl(line);
rev(line);
printf("%s\n", line);
return 0;
}
void remnl(char *s) { s[strlen(s) - 1] = 0; }
#include <stdio.h>
#include <string.h>
#include <conio.h>
int main(void) {
char r[256];
int i, d;
printf("\nEnter the word you want to reverse : ");
gets_s(r, sizeof(r));
d = strlen(r) - 1;
for (i = d; i >= 0; i--) {
printf("%c", r[i]);
}
_getch();
return 0;
}

Processing outputs of multiple inputs in C

It's not something trivial but I would like to know the best way to process multiple outputs, for example:
Input
First line of input will contain a number T = number of test cases. Following lines will contain a string each.
Output
For each string, print on a single line, "UNIQUE" - if the characters are all unique, else print "NOT UNIQUE"
Sample Input
3
DELHI
london
#include<iostream>
Sample Output
UNIQUE
NOT UNIQUE
NOT UNIQUE
So how can I accomplish outputs like that? My code so far is:
int main(int argc, char *argv[])
{
int inputs, count=0;
char str[100];
char *ptr;
scanf("%d",&inputs);
while(inputs-- >0)
{
scanf("%s",str);
for(ptr=str; *ptr!='\0';ptr++)
{
if( *ptr== *(ptr+1))
{
count++;
}
}
if(count>0)
{
printf("NOT UNIQUE");
}
else
{
printf("UNIQUE");
}
}
}
But the above will obviously print the output after each input, but I want the output only after entering all the inputs, if the user enters 3, then the user have to give 3 strings and after the output will be given whether the given strings are unique or not. So I want to know how can I achieve the result given in the problem. Also another thing I want to know is, I am using an array of 100 char, which it can hold a string up to 100 characters, but what do I have to do if I want to handle string with no limit? Just declaring char *str is no good, so what to do?
Hope this helps:
#include <stdio.h>
int main(int argc, char *argv[])
{
int inputs,count=0;
char str[20];
scanf("%d",&inputs);
char *ptr;
char *dummy;
while(inputs-- >0)
{
scanf("%s",str);
for(ptr=str; *ptr!='\0';ptr++)
{
for(dummy=ptr+1; *dummy != '\0';dummy++)
{
if( *ptr== *dummy)
{
count=1;
}
}
if(count == 1)
break;
}
if(count>0)
{
printf("NOT UNIQUE");
}
else
{
printf("UNIQUE");
}
}
}
If you want to save stuff for later use, you must store it somewhere. The example below stores up to 10 lines in buf and then points str to the current line:
#include <stdlib.h>
#include <stdio.h>
#include <string.h> /* for strlen */
#include <ctype.h> /* for isspace */
int main(int argc, char *argv[])
{
int ninput = 0;
char buf[10][100]; /* storage for 10 strings */
char *str; /* pointer to current string */
int i;
printf("Enter up to 10 strings, blank to and input:\n");
for (i = 0; i < 10; i++) {
int l;
str = buf[i];
/* read line and break on end-of-file (^D) */
if (fgets(str, 100, stdin) == NULL) break;
/* delete trailing newline & spaces */
l = strlen(str);
while (l > 0 && isspace(str[l - 1])) l--;
str[l] = '\0';
/* break loop on empty input */
if (l == 0) break;
ninput++;
}
printf("Your input:\n");
for (i = 0; i < ninput; i++) {
str = buf[i];
printf("[%d] '%s'\n", i + 1, str);
}
return 0;
}
Note the two separate loops for input and output.
I've also rejiggled your input. I'm not very fond of fscanf; I prefer to read input line-wise with fgets and then analyse the line with strtok or sscanf. The advantage over fscanf is that yout strings may contain white-space. The drawback is that you have a newline at the end which you usually don't want and have to "chomp".
If you want to allow for longer strings, you should use dynamic allocation with malloc, although I'm not sure if it is useful when reading user input from the console. Tackle that when you have understood the basics of fixed-size allocation on the stack.
Other people have already pointed you to the error in your check for uniqueness.

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