Programming

//sort ascending n strings

#include <stdio.h>

int main()
{
  int n,i,j;
  char a[20];
  printf("How many strings?");
  scanf("%d",&n);
  
  for (i=1;i<=n;i++)
  {
    printf("a[%d]=",i);
    scanf("%s",&a[i]);
  }
    
  printf("\n");
  
  for (j=1;j<=n;j++)        //Here I want to write them, so I'm sure I've read them good
    printf("%s\n",a[j]);     //the problem apears here: Segmentation fault
    
  return 0;
}

#include <stdio.h>

int main(int argc, char **argv)
{
  int n=0,
      i=0,
      j=0;
  char a[20][80]={0x0};    /* this makes twenty 80 character-long strings */
  printf("How many strings?");
  scanf("%d",&n);  

  for (i=1;i<=n && i < 20;i++)
  {
    printf("a[%d]=",i);
    scanf("%s", a[i]);
  }

  printf("\n");

  for (j=1;j<=n  && j < 20;j++)        //Here I want to write them, so I'm sure I've read them good
    printf("%s\n",a[j]);     //the problem apears here: Segmentation fault - do not go past 20

  return 0;
}

//sort ascending two strings

#include <stdio.h>

int main()
{
  char a[10],b[10];
  char s1,s2;
  int i=0;
  
  printf("First string:"); scanf("%s",&a);
  printf("Second string:");scanf("%s",&b);
  printf("\n");
  printf("String 1:%s\n",a);
  printf("String2:%s\n\n",b);
  printf("Ascending order:\n");
  
  do
  {
    s1=a[i];
    s2=b[i];
    i++;
  }
  while (s1==s2);
  
  if (s1<s2)
  {
    printf("%s    ",a);
    printf("%s",b);
  }
  else
  {
    printf("%s    ",b);
    printf("%s",a);
  }
  printf("\n\n");
  return 0;
}

//sort ascending n strings
#include <stdio.h>

int main(int argc, char **argv)    //why int argc, char **argv ?
{
  int n=0,
      i=0,
      j=0,
      l=0;
  char s1,s2;
  char a[20][80]={0x0};    //what does {0x0} means?
  char aux[80];
  
  printf("How many strings?");
  scanf("%d",&n);  

  for (i=1;i<=n && i < 20;i++)
  {
    printf("a[%d]=",i);
    scanf("%s", a[i]);
  }

  printf("\n");

  for (j=1;j<=n  && j < 20;j++)     
    printf("%s\n",a[j]);     

  for (i=1;i<=n-1 && i<20;i++)        //a[i] and a[i+1] so i goes to i<=n-1 ?
  {
    do
    {
      s1=a[i][l];
      s2=a[i+1][l];
      l++;
    }
    while(s1==s2);
    
    if (s1<s2)
    {
      aux=a[i];        //invalid array assignment
      a[i]=a[i+1];    //invalid array assignment
      a[i+1]=aux;    //invalid array assignment
    }
  }
    
  for (j=1;j<=n  && j < 20;j++)        
    printf("%s\n",a[j]);    
    
  return 0;
}