comparing strings in a structure pointer in C - c

Question

#include <stdio.h>
#include<stdlib.h>
#include<string.h>
struct person {
char user[50];
char password[50];
int amount;
};
int i=0;
int h=0;
int *n=&h;
struct person *p = NULL;
void adduser();
int main()
{
int x;
printf("Welcome to the bank\n");
printf("what would you like to do\n");
printf("type 1 to add a user\n");
printf("type 2 to add to balance\n");
printf("type 3 to take from balance\n");
printf("type 4 to check from balance\n");
scanf("%d%*c",&x);
if(x==1){
adduser();
}
else if (x == 2){
printf("2");
}
else if (x == 3){
printf("3");
}
else if (x == 4){
printf("4");
}
else{
main();
}
}
void adduser(){
struct person *temp = realloc(p, *n * sizeof(struct person));
if (temp != NULL)
p = temp;
printf("n=%d\n",*n-1);
printf("enter your new username\n");
scanf("%s",&(p+*n)->user);
int o=*n-1;
for (i;i<=o;i++)
{
if(strcmp((p+*n)->user,(p+i)->user) == 0)
{
printf("user already exists");
adduser();
}
}
printf("enter your new password\n");
scanf("%s",(p+*n)->password);
*n+=1;
main();
}
hello I'm a beginner with C I'm trying to see i have string the user input similar to one in my structure using this code.
for (i;i<=o;i++)
{
if(strcmp((p+*n)->user,(p+i)->user) == 0)
{
printf("user already exists");
adduser();
}
}
my code is supposed ask the user to enter their new user(at least what i posted) and checks if a similar user exists but my loop gets ignored i don't know what to do with it . i feel like my problem lies elsewhere but i cant figure it out. Also i might have done fundamental mistakes because I'm very new to structures and pointers.
i tried searching online for solutions but i couldn't find a similar situation.

Answer 1

This code is clearly in error:
struct person *temp = realloc(p, *n * sizeof(struct person));
since we're almost immediately going to do:
scanf("%s",&(p+*n)->user);
this really needs to read
struct person *temp = realloc(p, (*n + 1) * sizeof(struct person));
In addition,
for (i;i<=o;i++)
is clearly wrong and should be
for (i=0;i<=o;i++)
and as dxiv points out, i really should be declared in this for loop rather than as a global.
Incidentally, are you having trouble with loops? I don't see that recursive call of main() much. It's really clever, but this code works well only if compiled with optimizations on (which in turn is harder to debug). I'd advise replacing
else{
main();
}
and the other calls to main() with an infinite loop around all of main() (which eventually will have a loop exit condition or a conditional break; statement on the input ladder.