Need help with "if" statements

I am trying to create a vending machine program using "if" statements and I need to get the user to “insert” their money. Since they can’t physically insert money, the program needs to ask them how much they wish to insert and have to check and see if they entered at least $1.00 (using the “if” statements). If they do not insert at least $1.00, it will give them an error message and NOT give them the option to purchase a drink.

So far this is the coding that I have done using the Miracle C compiler. When I try to compile it, it gives me an error. I am just starting out getting familiarized with the C language and any help would be appreciated kindly.

Code:

---

#include <stdio.h>

int main()
{   
 
  printf ("%s","Welcome to Harry's Vending Machine\n");
 
  printf("Enter a value:\n");
 
  if (a == 1)
    printf ("\nPress 1 for 7 up\n");
   
    printf ("\nPress 2 for Coca Cola\n");
   
    printf ("\nPress 3 for Pepsi\n");
   
    printf ("\nPress 4 for Bottled Water\n");
   
    printf ("\nPress 5 for Dr. Pepper\n");
   
    printf("Thank you for your purchase\n");
   
    printf ("\nEnjoy your refreshing drink and don't forget your change\n");
    exit(0);
   
  if ("d > a")
 
    printf("Please insert correct amount\n");
   
    scanf("a");
   
return (0);

}

---

You need to put braces around your if statements. The form is :

Code:

---

if(condition)
{
      code to execute if condition is true
}

---

Further, I don't quite know where you get the value of a.
Also "d > a" is a string, not a condition. d > a, on the other hand, is.

You have this:

Code:

---

if (a == 1)

---

What is that going to do? You are doing a test on a variable that has not been declared (or initialised). Same story here:

Code:

---

if ("d > a")

---

Declare those variables first, and always make sure they hold some meaningful value before you attempt to use the value.

Next, you are not using scanf correctly:

Code:

---

scanf("a");

---

Can you see what you are missing?

Fix those problems and see where you are at. Also, is there any reason why you must use the Miracle C compiler? I understand that it is an old piece of poo - There are some fairly decent free ones out there these days. Bloodshed produces a nice IDE which utilises the GNU C compiler.

A good start: variable a is not even defined or used, you should really declare a double at the beginning of main. Next, scanf examines a format string, and tries to convert user input accordingly and then puts it in a variable. Learn how to use it correctly, and then learn why scanf is bad, and use other methods of input.

Code:

---

scanf("%1.2f", &a);

---

should help you out.
To let your customer choose their drink, you'll have to use scanf to get another value for their choice (preferably stored in another, different variable). Then depending on what the choice is, you give them their drink! :D

Quote:

---

Originally Posted by kermit

You have this:

Code:

---

if (a == 1)

---

What is that going to do? You are doing a test on a variable that has not been declared (or initialised). Same story here:

Code:

---

if ("d > a")

---

Declare those variables first, and always make sure they hold some meaningful value before you attempt to use the value.

Next, you are not using scanf correctly:

Code:

---

scanf("a");

---

Can you see what you are missing?

Fix those problems and see where you are at. Also, is there any reason why you must use the Miracle C compiler? I understand that it is an old piece of poo - There are some fairly decent free ones out there these days. Bloodshed produces a nice IDE which utilises the GNU C compiler.

---

Can you please help me correctly declare a variable because everytime I try to do it I get an error. I am using Miracle C because I think it's easier for someone that is just starting out.

Quote:

---

Originally Posted by Harryt123

I am using Miracle C because I think it's easier for someone that is just starting out.

---

I think using Miracle C is quite admirable for someone just starting out. It will not tell you when it is doing something wrong with correct code. Trying to guess at things you don't understand when the compiler is of no help and even harmful will truly make your learning experience a hard-earned adventure.

Consider a good free compiler: Dev-C++. And search the board for "Miracle C" to see just how highly regarded it really is.

Miracle C is the "Herbert Schildt" of compilers.


Quzah.

> Miracle C is the "Herbert Schildt" of compilers.
At least you could set fire to a HS book - Miracle C has no redeeming features at all.

Do you understand this code?

Code:

---

#include <stdio.h>
#include <string.h>
#include <conio.h>

int main ( void )
{
  int a;
  char name[15];

  strcpy(name, "peter");

  printf("Hello, %s, how old are you? ");
  scanf("%d", &a);
  printf("So you are %d years old!", a);
 
  getch();
 
  return 0;
}

---

If not, read up on how to read strings in using strcpy, and declaring variables.
I appogise to the old syntax ir: using conio.h but I was taught C in 1997 when
I was 14.

Well those are some nice tricks. Why not explicitly list the arguments for printf though, so the compiler does not have to guess?

What happens if there is more than one string?

Code:

---

#include <stdio.h>
#include <string.h>

int main ( void )
{
  int a;
  char name[15];
  char string[15];

 
  strcpy(name, "peter");
  strcpy(string, "lalalalal");

  printf("Hello, %s, how old are you? ");
  fflush(stdout);
  scanf("%d", &a);
  printf("So you are %d years old!\n", a);
 
  return 0;
}

---

My output: Hello, lalalalal, how old are you?

Now if I change the printf to look like this:

Code:

---

printf("Hello, %s, how old are you? ", name);

---

Then I get the expected output:

Hello, peter, how old are you?

And if you know enough to apologise for using getch with conio.h, why don't you know enough not to include it?

Quote:

---

Originally Posted by kermit

Well those are some nice tricks. Why not explicitly list the arguments for printf though, so the compiler does not have to guess?

What happens if there is more than one string?

Code:

---

#include <stdio.h>
#include <string.h>

int main ( void )
{
  int a;
  char name[15];
  char string[15];

 
  strcpy(name, "peter");
  strcpy(string, "lalalalal");

  printf("Hello, %s, how old are you? ");
  fflush(stdout);
  scanf("%d", &a);
  printf("So you are %d years old!\n", a);
 
  return 0;
}

---

My output: Hello, lalalalal, how old are you?

Now if I change the printf to look like this:

Code:

---

printf("Hello, %s, how old are you? ", name);

---

Then I get the expected output:

Hello, peter, how old are you?

And if you know enough to apologise for using getch with conio.h, why don't you know enough not to include it?

---

Thank you so much for your help and everyone that posted above you. I appreciate it greatly as I am just starting out and I'm sure you guys have more experience then I do. I just have a couple of questions to ask with two lines of codes that are errors.
In dev-C++ which I am using over Miracle C because it at least shows which line is in error.
[warning] comparison between pointer and integer.

Code:

---

{
  if("%d" > 1)

---

than the next one that is giving me trouble is the following line.
[warning] passing arg 1 of `scanf' from incompatible pointer type

Code:

---

scanf(&a,&d);

---

I just pasted the two exact lines of code and not the entire code to make it easier to know exactly which code I was reffering to that had the errors, hopefully this will help.

The first error references the fact that, again "%d" is a string (or also a character pointer, as is said in the error, but don't worry about that yet.), so the compiler cannot compare it with the value 1, for it to work out, d would have to be an integer of some sort.

The second error is because the format of scanf you've given is incorrect. It is supposed to be :

Code:

---

scanf(format string ,variables in which to put values read )

---

Therefore, a valid use of scanf would be :

Code:

---

scanf("Input an integer : %d", &a); /*  Given that a is declared as an integer  */

---

Yours, however, does not do that.

Cheers.

Quote:

---

Originally Posted by Happy_Reaper

The first error references the fact that, again "%d" is a string (or also a character pointer, as is said in the error, but don't worry about that yet.), so the compiler cannot compare it with the value 1, for it to work out, d would have to be an integer of some sort.

The second error is because the format of scanf you've given is incorrect. It is supposed to be :

Code:

---

scanf(format string ,variables in which to put values read )

---

Therefore, a valid use of scanf would be :

Code:

---

scanf("Input an integer : %d", &a); /*  Given that a is declared as an integer  */

---

Yours, however, does not do that.

Cheers.

---

Thank you so much everyone for the time and help you are giving me and I appreciate it kindly. I am going to post the revised version of my coding and please can you check if everything looks better than it was before. I am having a tiny error (null) Parse Error, expecting `'}''
'' other than that everything seems to be much better.

Code:

---

#include <stdio.h>
#include <string.h>
int main()
{ 
  int a;
  char name[1];
  int d=1;
  printf ("%s","Welcome to Harry's Vending Machine\n");
  printf("Enter a value:\n");
  scanf("%d",&a);
  { 
  if(a >= 1)
{           
    printf ("\nPress 1 for 7 up\n");
    printf ("\nPress 2 for Coca Cola\n");
    printf ("\nPress 3 for Pepsi\n");
    printf ("\nPress 4 for Bottled Water\n");
    printf ("\nPress 5 for Dr. Pepper\n");
    scanf ("%d", 5);
    printf("Thank you for your purchase\n");
    printf ("\nEnjoy your refreshing drink and don't forget your change\n");     
  } 
  else {
  printf("Please insert correct amount\n");
  scanf("%d", &a);
  }

---

Code:

---

printf("Enter a value:\n");
  scanf("%d",&a);
  { // just delete this brace. It's not necessary.

---

Your 'name' is only one character in length.
Your scanf just has a 5 in it. It should have a variable, and be using the & to store in said variable.
You are missing a closing }. Fix this issue by indenting four spaces every time on the line following the {, ligning up the items for that block, and unindending four spaces every time you put a }. Like so:

Code:

---

int main( void )
{
    abc
    def
    {
        abc
        def
        {
            abc
            def
        }
        ghi
        jkl
    }
    ghi
    jkl
}

---

Nice and clean.


Quzah.

Quote:

---

Originally Posted by citizen

Code:

---

printf("Enter a value:\n");
  scanf("%d",&a);
  { // just delete this brace. It's not necessary.

---

---

Still wouldn't fix it. They're missing the one for main.


Quzah.

Quote:

---

Originally Posted by citizen

Code:

---

printf("Enter a value:\n");
  scanf("%d",&a);
  { // just delete this brace. It's not necessary.

---

---

I thought that was it and deleted it but that just made the whole thing much worse and gave more errors.

Running the most recent post through a beautifier, this is what you have:

Code:

---

#include <stdio.h>
#include <string.h>
int main()
{
  int a;
  char name[1];
  int d=1;
  printf ("%s","Welcome to Harry's Vending Machine\n");
  printf("Enter a value:\n");
  scanf("%d",&a);
  { 
      if ( a >= 1 )
      {
        printf ("\nPress 1 for 7 up\n");
        printf ("\nPress 2 for Coca Cola\n");
        printf ("\nPress 3 for Pepsi\n");
        printf ("\nPress 4 for Bottled Water\n");
        printf ("\nPress 5 for Dr. Pepper\n");
        scanf ("%d", 5);
        printf("Thank you for your purchase\n");
        printf ("\nEnjoy your refreshing drink and don't forget your change\n");     
      }
      else
      {
        printf("Please insert correct amount\n");
        scanf("%d", &a);
      }

---

Following good indentation habits is for the new to help write good code.

[edit]FAQ > How do I... (Level 1) > How do I get a number from the user (C)

Code:

---


/* aa.c */



#include <stdio.h>
#include <string.h>
int main()
{ 
  int a,d ;
  char name[1];
  d=1;
  printf ("%s","Welcome to Harry's Vending Machine\n");
  printf("Enter a value:\n");
 

       
    printf ("\nPress 1 for 7 up\n");
    printf ("\nPress 2 for Coca Cola\n");
    printf ("\nPress 3 for Pepsi\n");
    printf ("\nPress 4 for Bottled Water\n");
    printf ("\nPress 5 for Dr. Pepper\n");
    scanf ("%d", &a);


   
  if(a >= 1)
{ 

    printf("Thank you for your purchase\n");
    printf ("\nEnjoy your refreshing drink and don't forget your change\n");     
  } 
  else {
  printf("Please insert correct amount\n");
  scanf("%d", &a);
  }
}

---

do not need d
do not need name[]
menu before enter a value
prog not done are you going to do something with each diff selection?

anyway

Code:

---


if (test;) { statement; }
 else if (test;) {statement;}

---

Quote:

---

Originally Posted by kryptkat

Code:

---


/* aa.c */



#include <stdio.h>
#include <string.h>
int main()
{ 
  int a,d ;
  char name[1];
  d=1;
  printf ("%s","Welcome to Harry's Vending Machine\n");
  printf("Enter a value:\n");
 

       
    printf ("\nPress 1 for 7 up\n");
    printf ("\nPress 2 for Coca Cola\n");
    printf ("\nPress 3 for Pepsi\n");
    printf ("\nPress 4 for Bottled Water\n");
    printf ("\nPress 5 for Dr. Pepper\n");
    scanf ("%d", &a);


   
  if(a >= 1)
{ 

    printf("Thank you for your purchase\n");
    printf ("\nEnjoy your refreshing drink and don't forget your change\n");     
  } 
  else {
  printf("Please insert correct amount\n");
  scanf("%d", &a);
  }
}

---

do not need d
do not need name[]
menu before enter a value
prog not done are you going to do something with each diff selection?

anyway

Code:

---


if (test;) { statement; }
 else if (test;) {statement;}

---

---

actually now that everything seems fine because whenever they put in the $1 value it is working perfectly because it takes them to the soda selection and they can select the soda of their choice. The only problem that I have right now is that I need to find out whenever they put in an incorrect about(anything under $1) it will take them to a message "insert correct amount." That's all I need done for right now. Thank you so much for your help I appreciate it :)

This is what I have so far if someone can look over my coding and let me know if everything is correct that would be appreciated. However, when I try to compile the code I am getting a syntax error towards the end which I just can't figure out what it might be from.

Code:

---

/* aa.c */
#include <stdio.h>
#include <string.h>
int main()
{ 
  int a;
  char name[1];
  printf ("Welcome to Harry's Vending Machine\n");
  printf("Enter a value:\n");
  {
  check: if ('a' >=1)
    scanf('a'==0);
    printf ("\nPress 1 for 7 up\n");
    printf ("\nPress 2 for Coca Cola\n");
    printf ("\nPress 3 for Pepsi\n");
    printf ("\nPress 4 for Bottled Water\n");
    printf ("\nPress 5 for Dr. Pepper\n");
    scanf ('a'==0);
    if('a' >= 1)
  {
    printf("Thank you for your purchase\n");
    printf ("\nEnjoy your refreshing drink and don't forget your change\n");     
  }
  else {
  printf("Please insert correct amount\n");
    while ( a < 1 ); 
}

---

Quote:

---

Originally Posted by Harryt123

Code:

---

/* aa.c */
#include <stdio.h>
#include <string.h>
int main()
{ 
  int a;
  char name[1]; /* An array of 1 item is pointless. */
  printf ("Welcome to Harry's Vending Machine\n");
  printf("Enter a value:\n"); /* Shouldn't you display the menu before asking for a choice? */
  {
  check: if ('a' >=1) /* If the letter (character) 'a' is greater than or equal to one... */
    /* 'check:' is a goto lable, which you never use. */
    scanf('a'==0); /* Did you even try compiling your code? */
    printf ("\nPress 1 for 7 up\n");
    printf ("\nPress 2 for Coca Cola\n");
    printf ("\nPress 3 for Pepsi\n");
    printf ("\nPress 4 for Bottled Water\n");
    printf ("\nPress 5 for Dr. Pepper\n");
    scanf ('a'==0); /* 'a' is the character constant for the letter a, not your variable. */
    if('a' >= 1) /* Same problem here... */
  {
    printf("Thank you for your purchase\n");
    printf ("\nEnjoy your refreshing drink and don't forget your change\n");     
  }
  else {
  printf("Please insert correct amount\n");
    while ( a < 1 );  /* Here is the only time you're comparing your variable a correctly. */
}

---

---

Commented. However there are a few more points, such as 'name' never being used, and the variable a being used uninitialized. Things like that. You need to read your chapter on using scanf over again, and learn how it works.


Quzah.

build on this simplified code.

Code:

---


/* aa.c */




#include <stdio.h>

int main()
{ 
  int a;
 
  printf ("Welcome to Harry's Vending Machine\n");
 
 

    printf ("\nPress 1 for 7 up\n");
    printf ("\nPress 2 for Coca Cola\n");
    printf ("\nPress 3 for Pepsi\n");
    printf ("\nPress 4 for Bottled Water\n");
    printf ("\nPress 5 for Dr. Pepper\n");

  printf("Enter a value:\n");


    scanf("%d",&a);
    if(a >= 1)
  {
    printf("Thank you for your purchase\n");
    printf ("\nEnjoy your refreshing drink \n");     
  }
 

}

---