#include<stdio.h>
#include<string.h>
#include<ctype.h>
int main(){
char inputstring[101];
char outputstring[101;
int encountered[256]={0};
int outputIndex=0;
printf("Enter the string:");
fgets(inputString, sizeof(inputString),stdin);
inputstring[strcspn(inputString,"\n")]=0;
for(int i=0; inputString[i]!='\0';i++){
char c =inputString[i];
if(!isalnum(c) && !isspace(c)){
printf("Invalid input.\n");
return 1;
}
if(encountered[(unsigned char)c]==0){
outputString[outputIndex++]=c;
encountered[(unsingned char)c]=1;
}
}
outputString[outputIndex]= '\0';
printf("output: %s\n, outputString);
return 0;
}