Program stops working when I input variables [closed] - c

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I want to do something in case the username is equal to "admin", but this error appears when I input username and pass.
#include <stdio.h>
#include <stdlib.h>
int main() {
char UserName[100];
char admin[6]="admin";
double Password;
int choice,result;
while (choice!=3){
printf("Username : ");
scanf("%s",&UserName);
printf("Password : ");
scanf("%d",Password);
char admin=admin;
if(strcmp(UserName, admin)&&(Password==1234))
{
printf(" enter your choice : ");
}
}
return 0;
}

Answer 1

I tried to minimize the changes to your code. See my attempt of a possibly working (not tested) alternative
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void) { // full definition with prototype
char UserName[100];
char admin[6] = "admin";
int Password; // changed to int
int choice = 0, result; // initialize choice
while (choice != 3) {
printf("Username : ");
// limit input, the & is wrong, check the return value of scanf
if (scanf("%99s", UserName) != 1) exit(EXIT_FAILURE);
printf("Password : ");
// match type of "%" and variable, check the return value
if (scanf("%d", Password) != 1) exit(EXIT_FAILURE);
// char admin = admin; // deleted
// strcmp returns 0 when the strings match
if ((strcmp(UserName, admin) == 0) && (Password == 1234))
{
printf("OK!\n"); // do something
}
// block structure messed up?
printf(" enter your choice : ");
if (scanf("%d", &choice) != 1) exit(EXIT_FAILURE);
}
return 0;
}

Answer 2

this error appears when i input username and pass.
because you have these 2 undefined behaviors in your code :
scanf("%s",&UserName);
whose must be
scanf("%s",UserName);
and 'worst' :
scanf("%d",Password);
whose must be
scanf("%d", &Password);
else scanf try to write to an undefined address being the value of Password which is not initialized
May be the execution continue after scanf("%s",&UserName) but no chance it does after scanf("%d",Password) producing typically a segmentation fault
Note also Password has to be an int, or the format has to be something like "%g" but to use a floating point value for a password is very improbable
Out of that you have an other undefined behavior in
while (choice!=3){
because choice is never initialized, but that time the effect is not 'catastrophic' like it is with scanf("%d",Password);
Also what do you expect with :
char admin=admin;
that line must be removed because there is no reason to have it
And finally a closing '}' is missing before return 0;

Answer 3

I updated your code with some things that were missing:
Added string.h include that was required for strcmp
Removed char admin = admin
Updated the Password scanf to use the proper type
Always try to pay attention to the compiler and activate all warnings as errors when possible.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char UserName[100];
char admin[6] = "admin";
int Password;
int choice = 0;
while (choice != 3)
{
printf("Username : ");
scanf("%s", UserName);
printf("Password : ");
scanf("%d", &Password);
if (strcmp(UserName, admin) && (Password == 1234))
{
printf(" enter your choice : ");
}
return 0;
}
}