Replace multiple spaces by single space in C

Question

I want to repace multiple spaces in a string by single space, however my following code doesn't work. What's the logical mistake?

#include<stdio.h>
#include<string.h>
main()
{
char input[100];
int i,j,n,z=0;
scanf("%d",&n);
z=n;
for(i=0;i<n;i++)
scanf("%c",&input[i]);
for(i=0;i<n;i++)
{
    if(input[i]==' ' && (input[i+1]==' ' || input[i-1]==' '))
    {
        --z;
        for(j=i;j<n;j++)
        input[j]=input[j+1];
    }
}
for(i=0;i<z;i++)
    printf("%c",input[i]);
printf("\n");
}

Answer 1

You have to fix the following for loop. the limit of your for loop should be z and not n

for(j=i;j<n;j++)
input[j]=input[j+1];

by

for(j=i;j<z;j++)
input[j]=input[j+1];

BTW: the fist charachter get by your scanf() (which read charachters) is newline (\n). this newline come from the first scanf() of decimal(%d)

Answer 2

The scanf is giving you some problem: it reads the \n you give after inputting the length n. So, you will miss the last character since for loop exits. The already given answers are good enough. But if you want to follow your own logic, try this:

void main()
{
    char input[100];
    int i = 0,j,n = 0;
    while ((input[n] = getchar()) != '\n') {
        n++;
    }
    input[n] = '\0';
    while (i < n)
    {
        if(input[i]==' ' && (input[i+1]==' ' || input[i-1]==' '))
        {
            for(j=i;j<n;j++)
            input[j]=input[j+1];
            n--;
        }
        else
        {
            i++;
        }
    }
    printf("%s\n",input);
    printf("\n");
}

Answer 3

#include <stdio.h>
#include <stdlib.h>
void remove_blanks(char* s);

int main()
{
    char const s[] = {'1',' ',' ','2',' ',' ','3'};
    remove_blanks(s);
    printf("%s",s);
    return 0;
}

void remove_blanks(char* s){
    int i=0, delta=0, cnt=0;

    for (i=0;s[i];++i){
        if (s[i]==' ') cnt++;
        if (cnt>1){
            delta+=1;
            cnt=0;
        }
        s[i-delta]=s[i];
        if(delta>0) s[i]='\0';

    }
}

Answer 4

You cant try this simple code:

#include <stdio.h>

#define IN 1
#define OUT 0

int main() {
  int c, spaces, state;

  spaces = 0;
  state = OUT;  
  while ((c = getchar()) != EOF) {

      if ( c == ' ') {
           ++spaces;
           state = OUT;
       }
      else if (state == OUT) {
          state = IN;
          spaces = 0;
      }
      if (c == ' ' && spaces > 1 && state == OUT)
          c = 0;            
      putchar(c);
  }
  return 0;
}

Answer 5

#include<stdio.h>
#include<string.h>
int main(void)
    {
        char input[1000];
        int i=0;
        gets(input); 
        for(i=0;input[i]!='\0';i++)
        {
            if(input[i]!=' ' || input[i+1]!=' ')
                printf("%c",input[i]);
        }
        return 0;
    }

Answer 6

if(input[i]==' ' && (input[i+1]==' ' || input[i-1]==' '))

case " 1 3" : when i == 0 accses input[i-1] Out-of-Bounds

scanf("%d",&n);

remain newline, (input[0] <-- '\n')

fix to

scanf("%d%*c",&n);

#include <stdio.h>

char* uniq_spc(char* str){
    char *from, *to;
    int spc=0;
    to=from=str;
    while(1){
        if(spc && *from == ' ' && to[-1] == ' ')
            ++from;
        else {
            spc = (*from==' ')? 1 : 0;
            *to++ = *from++;
            if(!to[-1])break;
        }
    }
    return str;
}

int main(){
    char input[]= "  abc   de  f  ";

    printf("\"%s\"\n", uniq_spc(input));//output:" abc de f "
    return 0;
}