In the seat reservation that I am working on, I used if(p.name == passengername)to get user input to update its input. But it says error.
forbids comparison between pointer and integer [-fpermissive]
if(p.name == passengername)```
I declared passengername as char but it is not working. Am I doing it wrong? I assumed that p.name is a char so that I can compare it to the char passengername that I declared.
And what do I need to do to get user's input in chooseseat() so that I can use it in reserve(); When I print it the p.seatcol and p.seatrow in fprintf displays 0. What do I need to do to save users input in chooseseat(); to reserve();?
Below is the part of my sample program.
#include<stdio.h>
#include<malloc.h>
#include<string.h>
#define ROWS 11
#define COLS 8
#define PASSENGERSIZE sizeof(passenger)
typedef struct{
char city[20], name[50], seatcol;
int age, seatrow, id;
unsigned int seatnum;
}passenger;
void chooseseat();
void reserve(){
passenger p;
FILE *fp, *fp1;
fp=fopen("passenger.txt", "a ");
fp1=fopen("passenger1.txt", "a ");
printf("\n\t\t\tEnter your name:");
scanf(" %s",p.name);
chooseseat();
write(&p, PASSENGERSIZE, 1, fp1);
fprintf(fp, " %s\t%d%c",p.name, p.seatrow,p.seatcol);
fclose(fp);
fclose(fp1);
}
void chooseseat(){
passenger p;
// Read the user input until it reserves a seat or request quitting.
// Read user input.
printf("\nEnter your seat number: (EX: 1A)");
scanf(" %d%c",&p.seatrow, &p.seatcol);
// Check if the seat requested is valid entry.
if (p.seatrow > 0 && p.seatrow < ROWS &&
p.seatcol >= 'A' && p.seatcol <= 'A' COLS){
// Input range is valid, check if seat is already taken.
if (seat[p.seatrow - 1][p.seatcol - 'A'] != 'X'){
// Seat is available, reserve it and break the loop.
seat[p.seatrow - 1][p.seatcol - 'A'] = 'X';
printf("Congratulations. Your seat number is %d%c\n",p.seatrow,p.seatcol);
}
else{
// Seat is already taken.
printf("Seat is already taken. Choose another seat? (Y/N)\n.");
scanf(" %c", &answer);
if (answer != 'Y'){
printf("Your data will be not saved and will be returned to main menu.\n");
}
}
}
else{
// Input range is invalid.
printf("Invalid seat row/col,\n");
}
}
void display(){
passenger p;
FILE *fp, *fp1;
fp=fopen("passenger.txt", "r");
fp1=fopen("passenger1.txt", "r");
while(fread(&p, PASSENGERSIZE, 1, fp1)){
printf(" \n%s\t%d%c",p.name,p.seatrow,p.seatcol);
}
fclose(fp);
fclose(fp1);
}
void update(){
FILE *fp, *fp1, *fp2;
char passengername;
int found=0;
fp=fopen("passenger.txt", "r");
fp1=fopen("passenger1.txt", "r");
fp2=fopen("temp.txt","w");
printf("\n\t\t\tEnter roll number to update: ");
scanf(" %c", &passengername);
while(fread(&p, PASSENGERSIZE, 1, fp1)){
if(p.name == passengername){
found=1;
displayseat();
printf("\n\t\t\tUpdate your seat number: (EX: 1A)");
scanf(" %d%c",&p.seatrow, &p.seatcol);
}fwrite(&p, PASSENGERSIZE, 1, fp2);
}
fclose(fp);
fclose(fp1);
fclose(fp2);
}
int main(){
int selection;
do{printf("\n\t\t\t\t\t************WELCOME TO C AIRLINES********");
printf("\n\t\t\t\t\t CHOOSE A MENU OPTION: ");
printf("\n");
printf("\n\t\t\t\t\t [1] ENTER A RESERVATION");
printf("\n\t\t\t\t\t [2] EDIT A RESERVATION");
printf("\n\t\t\t\t\t [3] DISPLAY RESERVATION");
printf("\n\t\t\t\t\t [0] EXIT");
printf("\n\t\t\t\t\t=============================\n");
printf("\n\t\t\t\t\tPlease Enter Any : ");
scanf("%d",&selection);
switch(selection){
case 1: reserve();
break;
case 2: update();
break;
case 3: display();
break;
default:
break;
}
}while(selection!=0);
}
CodePudding user response：
Your passengername is a single char.
For one, the compiler considers that a single integer (of small width), this is what causes your error.
For another, you need more than one char there, since you want to store a name. Use a char array like you did for p.name.
Then what you want to do is compare strings via pointers to them, not pointers.
So switch from == (comparing pointers) to strcmp(). ( https://en.cppreference.com/w/cpp/string/byte/strcmp )
Or even better, strncmp().
CodePudding user response：
There's a bunch of issues here.
I'll concentrate just on the update() function, because this is the place of your current issue.
Firstly, the code around the reported compilation error is using a variable named p. This variable has not been declared in the scope of function update(). Looking at the rest of your code, reading a few tutorials on C variable scope would be good.
The code is comparing p.name (char[50]) with passengername (char). The reason you're seeing this error is the char-array p.name ultimately is treated as a pointer, whereas passengername is a single character (perhaps you meant this to be a char-array too?). The single character is basically a small integer (1 byte).
This means that the statement:
if ( p.name == passengername )
resolves to:
if ( pointer-to-array-of-char == char )
which degrades to:
if ( pointer == number )
I can only guess at what the intention of the code is, but perhaps something like this is more what you desired:
void update()
{
FILE *fp, *fp1, *fp2;
passenger p; // <<-- HERE define 'p'
char passengername[sizeof(passenger.name)]; // <<-- HERE array, not char
int found=0;
fp = fopen("passenger.txt", "r");
fp1 = fopen("passenger1.txt", "r");
fp2 = fopen("temp.txt","w");
printf("\n\t\t\tEnter roll number to update: ");
fgets( passengername, sizeof(passenger.name), stdin ); // <<-- HERE fgets()
// TODO, Handle \n from fgets()
while( fread( &p, sizeof(passenger), 1, fp1 ) )
{
if ( strcmp( p.name, passengername ) == 0 ) // <<-- HERE strcmp()
{
found=1;
displayseat();
printf( "\n\t\t\tUpdate your seat number: (EX: 1A)" );
scanf( " %d%c", &p.seatrow, &p.seatcol );
}
fwrite( &p, sizeof(passenger), 1, fp2 );
}
fclose(fp);
fclose(fp1);
fclose(fp2);
}
- Errors and omissions expected. I made no attempt to fix all the errors in the code.