Input: a2b3c4 and Output: aabbbcccc

Question

The code I've written is not producing any output. It just takes the string as an input:

#include<stdio.h>
#include<conio.h>
#include<string.h>

int main() {
    char str[100];
    int i,size,s,pos;
    scanf("%s", &str);
    size=strlen(str);
    for(i=0;i<size;i++) {
        if((str[i]>=65 && str[i]<=90) || (str[i]>=97 && str[i]<=122)) {
            i++;
        } else {
            if(str[i]>='0' && str[i]<='9') {
                for(s=0;s<str[i];s++) {
                    printf("%s", str[i-1]);
                }
            }
            i++;
        }
    }
}

Answer 1

This whole code has many errors:

• You try to print a single character with %s, which is for strings. This leads to undefined behavior -- the correct conversion for a single character is %c.
• You loop until some "digit character" like '3'. You want to loop until the number 3 instead. Subtract '0' to achieve this.
• Doing scanf("%s", ...) is potential undefined behavior, it will eventually overflow any buffer. You might want to read my beginners' guide away from scanf(). In short, at least add a field width, in your case scanf("%99s", ...)
• scanf() expects a pointer to where to put the data, but str already evaluates to a pointer to the first array element. Therefore adding & is wrong here, leading to more undefined behavior.
• Always check the return value of functions that might fail. If your scanf() fails to convert something, your str stays uninitialized and the following strlen() is undefined behavior.
• Your code uses ASCII values, which is very common, but not mandated; this way, it won't work on machines not using ASCII.

It's not even necessary to use a buffer for what you want to achieve, a single character to save the last character read is sufficient, like this (the other issues are fixed in this example as well):

#include <stdio.h>
#include <ctype.h>

int main(void)
{
    int c;
    int l = EOF;

    while ((c = getchar()) != EOF)
    {
        if (isdigit(c) && isalpha(l))
        {
            for (int i = 0; i < c-'0'; ++i)
            {
                putchar(l);
            }
        }
        l = c;
    }

    putchar('\n');
    return 0;
}

---

As some further advice:

• Compile with compiler warnings enabled, e.g. when using gcc, add these flags:

  -std=c11 -Wall -Wextra -pedantic
  

  this would have identified some of the problems in your code already.

• Read a good book on C and look up individual functions in manual pages (on a *nix system, try typing man 2 printf for example .. you can also just feed it to google and find web versions of these pages)

Answer 2

Try this simple code

#include<stdio.h>
#include<string.h>

int main() {
   char str[50];
    int i=0,j,k,c;
    printf("Enter  String :  ");
    scanf("%s",&str);
    for(i=0;i<strlen(str);) {
        for(j=0;j<str[i+1]-'0';j++) {
            printf("%c",str[i]);
        }
    i=i+2;
    }
}

Answer 3

You can follow this code.May be help you.It's similar to your code...

#include<stdio.h>
#include<conio.h>
#include<string.h>
int main()
{
char str[100],ch;
int i,len,s,pos,k;
scanf("%s", &str);
len=strlen(str);
int number=0;
for(i=0; i<len; i++)
{
    if((str[i]>='a' && str[i]<='z') || (str[i]>='A' && str[i]<='Z'))
    {
        for(k=0;k<number;k++)
        {
            printf("%c",ch);
        }
        ch=str[i];
        number=0;
    }
    else
    {
        number=number*10+(str[i]-'0');
    }
}
for(k=0;k<number;k++)
{
    printf("%c",ch);
}
printf("\n");

}

Answer 4

Here is a simple code:

#include <stdio.h>
#include <stdlib.h>
#include<string.h>
#define MAX 50
void main()
{
    char name[MAX],str1[MAX],str3[MAX];
    int str2[MAX],i,j,m,t=0;
    printf("Enter name: ");
    scanf("%s", name);
    printf("Your name is %s.", name);
    for(j=0,i=0;name[i]!='\0';i=i+2,j++)
    {
        str1[j]=name[i];
        str2[j]=name[i+1]-'0';
    }
    for(i=0;i<=strlen(str1);i++)
    {
        for(j=str2[i];j>0;j--)
        {
            str3[t]=str1[i];
            printf("%c",str3[t]);
            t++;
        }

    }
}

Answer 5

#include<stdio.h>
int main()
{
char str[200] , ch;
int ind , count;
scanf("%s" , str);
int len , start;
for(len=0 ; str[len] ; len++);
start=len ;
ind=count=0;
while( ind < len )
{
    ch = str[ind++];
    while(str[ind] >= '0' && str[ind] <= '9' )
        count = count * 10 + (str[ind++] - '0');
    while(count)
    {
        str[start++] = ch;
        count--;
    }
}
for(ind=len ;ind < start ;ind++)
    str[ind - len]=str[ind];
str[ind - len] = 0;
printf("%s" , str);
return 0;
}

Answer 6

Here is the brute force approach in C++

#include <iostream>
using namespace std;

int main() {
   string s = "a3b3c4";
   int n = s.length();
   string w = "";
   for(int i=0;i<n;i++) {
      if(s[i] >= '0' && s[i] <= '9') {
          for(int j=0;j<s[i]-'0';j++) {
              w += s[i-1];
          }
      }
   }
  cout<<w<<endl;
}

The output will be:

aaabbbcccc

Answer 7

def decompress_str(com):
    ls = []
    for i in range(0,len(com),2):
        times = int(com[i+1])
        while times:
            ls.append(com[i])
            times -= 1
    print("".join(ls))

input = "a2b3c4"
decompress_str(input) # output aabbbcccc

Here:

1. I'm taking every even index(0,2,4) as the alphabet, and printing it for odd index(1,3,5) times. Appending the output to a list.

2. Later, I'm changing the list to a string using join().

Answer 8

#include<stdio.h>
#include<string.h>
int main()
{
char str[100];
int i=0,s;
scanf("%s",str);
while(str[i]!='\0')
{ 
    if(str[i]>='a' && str[i]<='z') 
    {
        i++;            
    }
    else if(str[i]>='A' && str[i]<='Z')
    { 
        i++; 
    }

    else if(str[i]>='0' && str[i]<='9')
        {

            for(s=0;s<str[i]-'0';s++)
            {
            printf("%c", str[i-1]);
            }
            i++;

        }

}

}