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I am writing a program of string pallindrome, code is compiling successfully but on running it accepting the string but nothing after that, the output window stays on hold with cursor blinking, help me what is wrong with this code.
I am using dev-c++
gets(ch); // the program stops here
p=ch;
while(ch!='\0')
{ p++;
size++;
}
for(i=0;i<20;i++)
{
if(c[i]==c[j])
printf("string is pallindrome");
else printf("string is not pallindrome");
}
getch();
return 0;
}
Here is the problem:
while(ch!='\0')
ch is a char array, and you are comparing it with a single char.
Also, size is not initialised.
I would suggest something like this:
size=0;
while(ch[size]!='\0')
{ p++;
size++;
}
or, using the pointer method:
while(*p!=0)
{
p++;
size++;
}
Also, instead of printing inside the for loop (which would make it print several times), use a flag variable.
You only need one loop, for example while (i < i).
Look at this example that will do the job:
#include <stdio.h>
#include <string.h>
/* in c99 use <stdbool.h> instead*/
typedef int bool;
#define true 1;
#define false 0;
int main(void)
{
char ch[20];
puts("enter the string: ");
gets(ch);
size_t size = strlen(ch);
bool pallindrome = true;
int j = size-1;
int i = 0;
while (i < j)
{
if(ch[i] != ch[j]) {
pallindrome = false;
break;
}
++i;
--j;
}
if (pallindrome)
printf("\"%s\" is pallindrome\n", ch);
else
printf("\"%s\" is not pallindrome\n", ch);
getch();
return 0;
}
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I am trying to make a program which prints all the possible permutations of the string "A?B?AB?" via replacing question marks with A or B. I can't understand why my code works the way it does and need help improving it.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char* rec(char s[8]){
int i=0;
for(;i<strlen(s);i++){
if(s[i]=='?'){
s[i]='A';
rec(s);
s[i]='B';
rec(s);
s[i]='?';
}
}
for(int k=0;k<strlen(s);k++){
if(s[k]=='?')
i=-1;
}
if(i!=-1)
printf("%s\n",s);
return s;
}
int main(){
char s[8]="A?B?AB?";
rec(s);
}
This should do the trick:
#include <stdio.h>
#include <string.h>
void rec(char *str, int size, int depth){
for (int i = depth; i < size; i++){
if (str[i] == '?'){
str[i] = 'A';
rec(str, size, i + 1);
str[i] = 'B';
rec(str, size, i + 1);
str[i] = '?';
return;
}
}
printf("%s\n", str);
}
int main(){
char s[8] = "A?B?AB?";
rec(s, strlen(s), 0);
}
It's much like August's solution, but I did decide to do some looping until it found the next question mark. That should avoid having too big of a callstack, which could lead to stack overflow, with really big strings. (Note: I didn't test it, so there could still be some minor problems)
You only need to look at one character at a time. Try this:
#include <stdio.h>
void PrintPermutationsFrom(int i, char s[])
{
if (s[i] == '?') {
s[i] = 'A';
PrintPermutationsFrom(i + 1, s);
s[i] = 'B';
PrintPermutationsFrom(i + 1, s);
s[i] = '?';
} else if (s[i] != '\0') {
PrintPermutationsFrom(i + 1, s);
} else {
puts(s);
}
}
void PrintPermutations(char s[])
{
PrintPermutationsFrom(0, s);
}
int main(void)
{
char s[] = "A?B?AB?";
PrintPermutations(s);
return 0;
}
I can't understand why my code works the way it does and need help improving it.
The rec code does simply too much in that after having replaced a ? with both A and B and called itself, it continues iterating over s and generates further output. That is too much because after the first found ?, the recursive invocations already have handled all following ? and generated all arrangements. To correct this, just insert a break; after s[i]='?';.
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So i have this problem where i have to input a string of unknown size with only lowercase letters then output the number of distinct letters.this is the main program
#include <stdio.h>
#include <ctype.h>
int test(char *T);
int main(){
char T[100];int i=-1,j=0,nd=0;
do{
gets(T);
}while((test(T))==1);
do {
i++;
j=i;
do{j++;
}while ((T[i]!=T[j])||((T[j])!=""));
if (T[j]=="")
nd++;
}while (T[i+1]!="");
and this is my function test
int test(char *T){
int i=-1,s;
do {
i++;
}while (((islower(T[i])==1))||(T[i]==""));
if ((T[i]=="")&&(i!=0))
s=0;
else s=1;
return s;
}
the problem is that i get a lot of warnings "comparison between integer and pointer" everytime i compare a char of the array T and i don't knowhow to fix that.your help would be much appreciated.
Update:So i tried fixing the program following your advices and this is the new main program
#include <stdio.h>
#include <ctype.h>
int test(char *T);
int main(){
char T[100];int i=-1,j=0,nd=0;
do{
gets(T);
}while((test(T))==1);
do {
i++;
j=i;
do{j++;
}while ((T[i]!=T[j])||((T[j])!='\0'));
if (T[j]=='\0')
nd++;
}while (T[i+1]!='\0');
printf("%d",nd);}
and this is function test
int test(char *T){
int i=-1,s;
do {
i++;
}while (((islower(T[i])==1))||(T[i]=='\0'));
if ((T[i]=='\0')&&(i!=0))
s=0;
else s=1;
return s;
}
I don't get anymore warnings and the program gets compiled with no problems but after i input the string in the execution nothing happens.
You function test should return 1 if the string contains only lowercase letters, and 0 otherwise. Unfortunately, it is not doing that.
You should first test if the character is a letter and then if it's a lowercase letter. Or more efficiently, you test if the character is in the range 'a' to 'z'.
Another problem of your code is the use of do while loops which makes the code difficult to understand and executes the loop once.
Here is a better implementation of the test function:
int test(char *T){
// reject empty strings
if(T[0] == '\0')
return 0;
// reject strings containing non lowercase letter
for(int i = 0; T[i] != '\0'; i++)
if((T[i] < 'a') || (T[i] > 'z'))
return 0;
// string is not empty and contains only lowercase letters
return 1;
Counting the different letters can be made more readable by using a for loop instead of a go while loop.
int nd = 0;
for(int i = 0; T[i] != '\0'; i++) {
for(int j = 0; j < i; j++) {
if(T[j] == T[i])
break; // quit inner loop
nd++;
}
}
This code examine each letter and see if it has been seen before. It is thus different from yours.
A problem in your code is the test (T[i]!=T[j])||((T[j])!='\0'). It should be && instead of ||, and testing if the end of string is reached should be performed first. The test should be (T[j]!='\0')&&(T[i]!=T[j]).
So my code is finally working here's the final main program
#include <stdio.h>
#include <ctype.h>
int test(char *T);
int main(){
char T[100];int i,j,nd=0;
do{
gets(T);
}while((test(T))==0);
for(i = 0; T[i] != '\0'; i++) {
j=i;
do{
j++;
}while ((T[j]!='\0')&&(T[j]!=T[i]));
if (T[j]=='\0')
nd++;
}
(#chmike i used the code you posted with a little adjustment on the loop)
and for the function test i used the code that posted #chmike as well.
Huge thanks to all of you guys for the help you provided :)
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I have to write a program that acts like a shell. I wrote the function that gets the input from the user. I also wrote the function that splits it into arguments. The first time I type something, it works well, but the second time, it prints different characters after the ones that I gave it. I don't have to print it in the program. I was just doing it to see if it works correctly. I read a bunch of stuff online, but I can't figure out my error. I suppose it is in makeArgs(), but I can't pinpoint it.
Also, when I give it an input, the readline function adds a \n at the end of the string. I suppose it is from the fact that I press the enter key. I managed to solve the issue, by manually replacing it, but I would like to know if it is normal.
Any help really be appreciated.
Thank You
Screenshot of Xterm after 2 inputs.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int getText();
int makeArgs();
char *textEntre;
size_t nbCharacters;
char **arguments;
int main (void)
{
while (1){
getText();
int nbArguments = makeArgs();
for(int i =0; i<5; i++){
printf("%s \n",arguments[i]);
}
for(int i=0; i<nbArguments; i++){//free the char ptrs at the end
free(arguments[i]);
}
}
free(textEntre);
free(arguments);
return 0;
}
int getText(){
size_t buffersize = 0;
nbCharacters = getline(&textEntre, &buffersize, stdin);
textEntre[nbCharacters-1] =' '; // when I press enter it regiter the enter as \n so I replace it with a space
return 0;
}
int makeArgs(){
arguments = (char **)malloc(sizeof(char*)*20);
int i;
int j = 0;
int k = 0;
int nbElem = 20; //the number of ptrs that can be in arguments
for(i = 0; i<nbCharacters; i++){
if(i == 20){ //increases the memory allocated if there are more than 20 arguments
nbElem = nbElem *2;
arguments = (char **)realloc(arguments, sizeof(char*)*nbElem);
}
if(textEntre[i] == '"'){ //checks for ""
i++;
while(textEntre[i] != '"'){
i++;
}
}
if(textEntre[i] == ' ' && textEntre[i-1] == ' '){ // eliminates useless spaces
j++;
}
else if(textEntre[i] == ' '){ //save a single argument
char * chptr;
chptr = (char *)malloc(i-j+1); //giving +1 for the \0 at the end
strncpy(chptr, &textEntre[j], i-j);
arguments[k] = chptr;
k++;
j = i +1;
}
}
return k;
}
chptr = (char *)malloc(i-j+1); //giving +1 for the \0 at the end
You properly allocated memory for that terminating \0, but where do you actually add that "\0 at the end"?
strncpy(chptr, &textEntre[j], i-j);
strncpy does not necessarily zero-terminate the destination buffer. You have to do it yourself.
In fact, in this specific application strncpy is a rather inappropriate function: it does not give you anything over ordinary memcpy and might be less efficient. You could just do
memcpy(chptr, &textEntre[j], i - j);
with potentially better efficiency. And, again, don't forget to zero-terminate the destination buffer.
Or you can use sprintf for the same purpose as follows
sprintf(chptr, "%.*s", i - j, &textEntre[j]);
which will produce a properly zero-terminated string in the destination. (Albeit you won't see sprintf used that way very often.)
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I am very new to programming and i wonder if there is a way to print out the first word of a string with gets() in C?
void printFirstWord(char string[])
{
int i;
for(i = 0; i < (string[i] != '\0'); i++)
{
if(isalpha(string[i]))
printf("%c", string[i]);
}
}
int main()
{
char string[MAX];
printf("Type in a scentence");
gets(string);
printFirstWord(string);
return 0;
}
This is the function that i have written and called in main right now. Is it because i have isalpha in the function?
In your implementation, you might add the following line in the loop:
if (string[i] == ' ')
break;
also, fix your loop parameters e.g. like this:
for (i = 0; i < strlen(string); i++)
Overall implementation in you way will be as below.
Consider choosing another design according to comments you got, e.g. not using gets.
void printFirstWord(char string[])
{
int i;
for (i = 0; i < strlen(string); i++)
{
if (isalpha(string[i]))
printf("%c", string[i]);
if (string[i] == ' ')
break;
}
}
int main()
{
#define MAX 100
char string[MAX];
printf("Type in a scentence\n");
gets_s(string, MAX);
printFirstWord(string);
getchar();
return 0;
}
I just found a way with isblank(); function, hope it helps to anybody :)
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main (){
int length, number, counter, position;
char name[50];
printf("Please type your complete name:\n");
gets(name);
//strlen();
//Returns the length of the given null-terminated byte string, that is, the number of characters in a character array
length=strlen(name);
//Counts each position until it finds a space
for(counter=0;counter<length;counter++)
{
if(isblank(name[counter]))
position=counter;
}
//Prints each character until the counter reaches the position number given by the counter variable
printf("\nThe first word you typed is: ");
for(number=0; number<=position; number++){
printf("%c", name[number]);
}
}
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i've wrote this c program but im always receiving the same inputed sentence as an output without any change! i've split every word in the string and then reversed their position but it didnt work well! any solutions please!
#include<stdio.h>
#include<conio.h>
#include<string.h>
int main ()
{
char A[81][81];
int t=0,j=1,k=0,l;
puts("Input a sentence (max 80 character)");
gets(A[0]);
while (A[0][t]!='\0')
{
if(A[0][t]=='\32')
{
j++;
t++;
k=0;
}
A[j][k]=A[0][t];
k++;
t++;
}
for (l=j;l>0;l--)
{
printf("%s",A[l]);
}
getch();
}
#include <stdio.h>
#include <string.h>
#include <conio.h>
int main(void){
char A[81][81] = {0};
int t=0,j=1,k=0,l;
puts("Input a sentence (max 80 character)");
scanf("%80[^\n]", A[0]);//'gets' has already been abolished, it should explore a different way.
while (A[0][t] != '\0'){
if(A[0][t] == ' '){
++j;
k=0;
while(A[0][t] == ' ')//Skip spaces
++t;
} else {
A[j][k++] = A[0][t++];
}
}
for (l=j;l>0;l--){
printf(" %s",A[l]);
}
puts("");
getch();
}