Hey guys I code a code coach and 4 from 5 was correct but on still wrong

Question

This is the code #include <iostream>
using namespace std;

int main() {
string m,j;
string b;
cin>>b>>m>>j;
b =b+' '+m+' '+j;
string alpha=" abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ";
char sal[200];
for(int uio=0;uio<200;uio++){
sal[uio]=0;
}
int poi=0;
for(int l=0;l<=sizeof(b);l++){
for(int k=0;k<=sizeof(alpha);k++){
if(b[l]==alpha[k]){
poi++;
sal[poi]=b[l];
}
}

}string nm="";
for(int o=poi;o !=0 ;o--){
for(int yu=0;yu<=sizeof(alpha);yu++){
if(sal[o] == alpha[yu]){
nm += alpha[yu];
}}}
cout<<nm;
}

Answer 1

Sakr Abdualsalam

Which Code Coach it is?