Why my goto command doing problems when compile?

Question

I coded a little program for math actions, but the goto command won't compile in some cases. Please help me.

Here is the code:

#include<stdio.h>
#define line11
#define YorN
#define End
#define Start

int main(void)
{
    float userNumber1,userNumber2;
    int mathAction;
    char tryAgain;
    Start:
    printf("Please write 2 numbers for your math action(a,b):\n");
    scanf("%f %f",&userNumber1,&userNumber2);
    Line11:
    printf("Please choose 1 of the following math actions by writing the action number :\n"
        "1)Adding a+b\n"
        "2)Subtracting a-b.\n"
        "3)Multiplying a*b.\n"
        "4)Dividing a/b.\n");
    scanf("%d",&mathAction);
    if (mathAction>4 || mathAction<1) //If the user pick something that's not 1-4 , then this if is going on.
    {
        printf("Grrrr.. pick between 1-4 ! \n");
        goto Line11;
    }
    if (mathAction==1)
    {
        printf("Adding %d + %d is %d\n",userNumber1,userNumber2,userNumber1+userNumber2);
    }
    if (mathAction==2)
    {
        printf("Subtracting %d - %d is %d\n",userNumber1,userNumber2,userNumber1-userNumber2);
    }
    if (mathAction==3)
    {
        printf("Multiplying %d * %d is %d\n",userNumber1,userNumber2,userNumber1*userNumber2);
    }
    if (mathAction==4)
    {
        if (userNumber2==0)
        {
            printf("You cant divide %d by 0 , its math error!\n");
            printf("Do you want to choose again? y/n\n");
            YorN:
            scanf("%c",&tryAgain)
            if (tryAgain !='y' || tryAgain !='n')
            {
                printf("Choose only yes or no by y for yes and n for no.");
                goto YorN;
            }
            if (tryAgain=='y')
            {
                goto Start;
            }
            if (tryAgain=='n')
            {
                goto End;
            }

        }
        printf("Dividing %d / %d is %.2f\n",userNumber1,userNumber2,userNumber1/userNumber2);
    }
    printf("Thanks for using my program !\nDo you want to try again? (Answer y/n)");
    scanf("%d",&tryAgain);
    if (tryAgain !='y' || tryAgain !='n')
    {
        printf("Choose only yes or no by y for yes and n for no.");
        goto YorN;
    }
    if (tryAgain=='y')
    {
        goto Start;
    }
    if (tryAgain=='n')
    {
        goto End;
    }
    End:
    system("PAUSE");
    return (0);
}

Here is the compile error:

q5.c: In function 'main':
q5.c:12:11: error: expected expression before ':' token
      Start:
           ^
q5.c:45:12: error: expected expression before ':' token
      YorN:
          ^
q5.c:69:15: error: expected identifier or '*' before ';' token
      goto YorN;
               ^
q5.c:73:16: error: expected identifier or '*' before ';' token
      goto Start;
                ^
q5.c:77:14: error: expected identifier or '*' before ';' token
      goto End;
              ^
q5.c:79:8: error: expected identifier or '*' before ';' token
     End:
        ^

I already tried everything to make this work, please help! By the way, one of the gotos is actually working.

the code is too long so its not letting me put the whole code , please download and check it. — Tom Bazak, Nov 21 '15 at 14:57
Try to create a [Minimal, Complete, and Verifiable Example](http://stackoverflow.com/help/mcve) which demonstrates your problem, and show that. And don't post images of text, especially *links* to images. A link may go stale and make your question worthless. If you have text, copy and paste it as text. — Some programmer dude, Nov 21 '15 at 15:00
Oh and by the way there are very few things you need to use `goto` for. Try and avoid it at all cost. — Some programmer dude, Nov 21 '15 at 15:02
@JoachimPileborg: Hmm, "try and avoid it at **all** cost" ... as you can always get along without `goto`, there cannot be "few things you need to use goto for" (which is close to almost never in practise;-) I'd say "unless avoiding `goto` will make your code significantly less readable". There is just no rule of thumb when to use `goto`. — too honest for this site, Nov 21 '15 at 15:07
This code is so 1970ies style. Spaghetti should be on a plate with a good sauce, not on the monitor. Did you convert some old BASIC code? I'd recomment to restructure without `goto` first, C has loop constructs with `break` and `continue`, `else`, etc. — too honest for this site, Nov 21 '15 at 16:46

score 3 · Answer 1 · answered Nov 21 '15 at 15:03

The problem is that you have

#define YorN
#define End
#define Start

in the beginning of your source. These preprocessor macros will be evaluated before compiling into nothing, so this code:

YorN:
goto YorN;

will become

:
goto;

Just remove them, since it make no sense to have them.

score 0 · Answer 2 · answered Nov 21 '15 at 15:00

Don't #define your goto labels. Your code was also missing a semicolon ( after scanf("%c",&tryAgain) at label YorN).

Here you can see the corrected version.

For the sake of completeness, I'll post the corrected code here:

#include<stdio.h>

int main(void)
{
    float userNumber1,userNumber2;
    int mathAction;
    char tryAgain;
     Start:
    printf("Please write 2 numbers for your math action(a,b):\n");
    scanf("%f %f",&userNumber1,&userNumber2);
    Line11:
    printf("Please choose 1 of the following math actions by writing the action number :\n"
     "1)Adding a+b\n"
     "2)Subtracting a-b.\n"
     "3)Multiplying a*b.\n"
     "4)Dividing a/b.\n");
    scanf("%d",&mathAction);
    if (mathAction>4 || mathAction<1) //If the user pick something that's not 1-4 , then this if is going on.
    {
        printf("Grrrr.. pick between 1-4 ! \n");
        goto Line11;
    }
    if (mathAction==1)
    {
        printf("Adding %d + %d is %d\n",userNumber1,userNumber2,userNumber1+userNumber2);
    }
    if (mathAction==2)
    {
        printf("Subtracting %d - %d is %d\n",userNumber1,userNumber2,userNumber1-userNumber2);
    }
    if (mathAction==3)
    {
        printf("Multiplying %d * %d is %d\n",userNumber1,userNumber2,userNumber1*userNumber2);
    }
    if (mathAction==4)
    {
        if (userNumber2==0)
        {
            printf("You cant divide %d by 0 , its math error!\n");
            printf("Do you want to choose again? y/n\n");
            YorN:
            scanf("%c",&tryAgain);
            if (tryAgain !='y' || tryAgain !='n')
            {
                printf("Choose only yes or no by y for yes and n for no.");
                goto YorN;
            }
            if (tryAgain=='y')
            {
                goto Start;
            }
            if (tryAgain=='n')
            {
                goto End;
            }

        }
        printf("Dividing %d / %d is %.2f\n",userNumber1,userNumber2,userNumber1/userNumber2);
    }
    printf("Thanks for using my program !\nDo you want to try again? (Answer y/n)");
    scanf("%d",&tryAgain);
    if (tryAgain !='y' || tryAgain !='n')
            {
                printf("Choose only yes or no by y for yes and n for no.");
                goto YorN;
            }
            if (tryAgain=='y')
            {
                goto Start;
            }
            if (tryAgain=='n')
            {
                goto End;
            }
 End:
 system("PAUSE");
 return (0);
}

score 0 · Answer 3 · answered Nov 21 '15 at 15:02

It won't compile because you have #defined the target symbols out of existence.

Other issues: In most of your printf() format strings you use %d without care for the actual type of your argument. Either cast your objects to int or use the correct type (%f for double).

One final issue: for what you are doing, you should be using functions and loops. Every one of your gotos can be replaced with an appropriate loop.

Hope this helps.

Why my goto command doing problems when compile?

3 Answers3