input validation- finding the area of a triangle and its type(isosceles, ect)

This is a discussion on input validation- finding the area of a triangle and its type(isosceles, ect) within the C Programming forums, part of the General Programming Boards category; I believe I am having some problems with my compiler. I believe everything is written correctly, and I was wondering ...

  1. #1
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    input validation- finding the area of a triangle and its type(isosceles, ect)

    I believe I am having some problems with my compiler. I believe everything is written correctly, and I was wondering if someone can give me heads up. Maybe I need a new compiler? or I saved the file incorrectly? or it's my operating system/computer.



    -----------------------------------------------------------------------------------
    Code:
    #include<stdio.h>
    #include<math.h>
     
    
    int main(void)
    {
        do
        {
        float a, b, c, s, area;
           char answer, y, Y, n, N;   
       
        printf("Enter the first side of the triangle: ");
        scanf_s("%f", &a);
        printf("Enter the second side of the triangle: ");
        scanf_s("%f", &b);
        printf("Enter the third side of the triangle: ");
        scanf_s("%f", &c);
        if ( a + b > c) || ( b + c > a) || ( a + c > b)
        {
            s = (a + b + c) / 2;
            area = sqrt(s * (s-a) * (s-b) * (s-c));
            printf("Area = %f\n", area);
           
            if ( a== b ) || ( b == c ) || ( a == c )
            {
                printf("Its an Isosceles Triangle\n");
                printf("Do you wish to continue with a new triangle?<y/n>");
                scanf_s("%c", &answer);
            }
            else if ( a == b ) && ( b == c )
            {
                printf("Its an Equilateral Triangle\n");
                printf("Do you wish to continue with a new triangle?<y/n>");
                scanf_s("%c", &answer);
            }
            else
            {
                printf("Its an Scalene Triangle\n");
                printf("Do you wish to continue with a new triangle?<y/n>");
                scanf_s("%c", &answer);
            }
        }
       
        while ( answer != y ) || ( answer != Y ) || ( answer != n ) || ( answer != N )
        {
            printf("You have made an invalid selection...\n");
            printf("Do you wish to continue with a new triangle?<y/n>");
            scanf("%c, &answer");
        }
        }
        while (answer == y || answer == Y);
       
        }
        return 0;
    }
    COMPILER ERROR-----------------------------------------

    ------ Build started: Project: triangles lab1b, Configuration: Debug Win32 ------
    triangles.cpp
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(23): error C2143: syntax error : missing ';' before '||'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(23): warning C4390: ';' : empty controlled statement found; is this the intent?
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(24): error C2143: syntax error : missing ';' before '{'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(28): error C2143: syntax error : missing ';' before '||'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(28): warning C4390: ';' : empty controlled statement found; is this the intent?
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(29): error C2143: syntax error : missing ';' before '{'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(34): error C2181: illegal else without matching if
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(34): error C2143: syntax error : missing ';' before '&&'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(34): warning C4390: ';' : empty controlled statement found; is this the intent?
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(35): error C2143: syntax error : missing ';' before '{'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(40): error C2181: illegal else without matching if
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(47): error C2143: syntax error : missing ')' before '!'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(47): error C2065: 'y' : undeclared identifier
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(47): error C2059: syntax error : ')'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(47): error C2143: syntax error : missing ')' before '!'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(47): error C2059: syntax error : ')'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(48): error C2143: syntax error : missing ';' before '{'
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(53): error C2065: 'y' : undeclared identifier
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(53): error C2065: 'Y' : undeclared identifier
    c:\temp\triangles lab1b\triangles lab1b\triangles.cpp(53): fatal error C1903: unable to recover from previous error(s); stopping compilation
    ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

  2. #2
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    Code:
                       
    if ( a + b > c) || ( b + c > a) || ( a + c > b)
    Above if statement (and other if statements in your program have the same problem), is incorrect. Correct would be:

    Code:
    if(( a + b > c) || ( b + c > a) || ( a + c > b))
    An if statement ends immediately after the first closing parentheses, which matches the number of opening parentheses. When one ( is matched by one ), *it's toast*.

    if(a+b>c)<=== the if statement has ended, since you matched the number of opening parenthesis.

  3. #3
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    woot

    thanks so much that was the problem can't believe I overlooked that lol. Now I gotta figure a way around that
    Code:
    while (( answer != 'y' ) || ( answer != 'Y' ) || ( answer != 'n' ) || ( answer != 'N' ))
    	{
    		printf("You have made an invalid selection...\n");
    		printf("Do you wish to continue with a new triangle?<y/n>");
    		scanf_s("%c, &answer");
    prob convert to a nested if statement that has a new variable to keep track if its true. wish C had bools would make things easier for me

  4. #4
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    Code:
        while (answer == y || answer == Y);
    You're also going to run into problems with this... y and Y are uninitialized numeric variables, not the letters "y" and "y". The results of the conditional statement will be undefined and unpredictable.

  5. #5
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    I've never quite wrapped my ahead around the need for bool's - if you can count from zero to one, and back again, what does bool give you extra -- besides a "whopee! I've got a bool", feeling.

    I'm not Catholic, but I decided to give them up in C++ for Lent last year, anyway.

  6. #6
    msh
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    Quote Originally Posted by Adak View Post
    I've never quite wrapped my ahead around the need for bools[...]
    They're unambiguous. And that's about it.

  7. #7
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    Quote Originally Posted by Adak View Post
    I've never quite wrapped my ahead around the need for bool's - if you can count from zero to one, and back again, what does bool give you extra -- besides a "whopee! I've got a bool", feeling.

    I'm not Catholic, but I decided to give them up in C++ for Lent last year, anyway.
    To give you one good example... The result of every "if" statement operates upon a boolean true or false produced by the expression in brackets behind it...

    if (6 > 3) == true, do it

    if (6 < 3) == false, don't do it

    Booleans are useful as very simple "go" "no go" flags that help organize program execution.

  8. #8
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    Quote Originally Posted by CommonTater View Post
    To give you one good example... The result of every "if" statement operates upon a boolean true or false produced by the expression in brackets behind it...

    if (6 > 3) == true, do it

    if (6 < 3) == false, don't do it

    Booleans are useful as very simple "go" "no go" flags that help organize program execution.
    OK, but EVERY expression being evaluated in C, reduces to either true (non-zero), or false (zero).

    So there is your "go, or no go", right there. Either the variable equals zero or it doesn't. Seems clear to me.

  9. #9
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    Quote Originally Posted by Adak
    Either the variable equals zero or it doesn't. Seems clear to me.
    What is not always clear is whether the integer value is a boolean value or an integral value. The use of a boolean type clarifies this.

    I suggest that you read up on the safe bool idiom: what motivated its invention and use, and its replacement by the explicit conversion function feature that will be introduced in the next version of C++.
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  10. #10
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    Thanks for that, laserlight. The "double-bang" trick was slick.

  11. #11
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    i think the logic of your program isn't quite correct... for eg..

    Code:
    if(( a + b > c) || ( b + c > a) || ( a + c > b))
    should be..

    Code:
    if(( a + b > c) && ( b + c > a) && ( a + c > b))
    as the condition for a triangle is that the sum of any two sides is greater than the third.. if you use ||, this condition may not be checked against.

    similarly, your program will not be able to detect equilateral triangles and categorize them as isosceles...

  12. #12
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    Not sure what is going on here but I am not getting the right results

    I am trying to get his to work, so far my output has been getting messed up, I am not sure if there is a way to clear the input buffer in C been trying to use scanf( "%*", &buf);.

    Code:
    #include <stdio.h>
    #include <math.h>
    
    int main(void)
    
    {
    	int side1, side2, side3;
    	int ok;
    	float s, area;
    	char y, n, Y, N, user_input, buf;
    	Y=1;
    	y=1;
    	N=0;
    	n=0;
    	ok=0;
    
    	do 
    	{
    
    		printf( "Enter the First side of the Triangle:\n" );
    
    		scanf( "%d", &side1);
    		
    		printf( "Enter the Second side of the Triangle:\n" );
    
    		scanf(  "%*", &buf);
    		scanf( "%d", &side2);
    		
    
    		printf( "Enter the Third side of the Triangle:\n" );
    
    		scanf(  "%*", &buf);
    		scanf(  "%*", &buf);
    		scanf( "%d", &side3);
    		
    
    		printf("%d\n, %d\n, %d\n", side1, side2, side3);
    
    if ((side1 + side2 <= side3) || (side1 + side3 <= side2) || (side2 + side3 <= side1))
    
    		{
    
    			printf( "Not a Valid Triangle\n" );
    
    		}
    
    		else if ((side1 == side2) && (side1 == side3))
    
    		{
    
    			printf( "Triangle is Equilateral\n" );
    
    			s = (side1 + side2 + side3)/2;
    
    			area=sqrt(s*(s-side1)*(s-side2)*(s-side3));
    
    			printf( "Area of the Triangle is:\n%d\n", area);
    
    		}
    
    	else if ((side1 != side2) && (side1 != side3) && (side2 !=side3))
    		{
    
    			printf( "Triangle is Scalene\n" );
    
    			s = (side1 + side2 + side3)/2;
    
    			area=sqrt(s*(s-side1)*(s-side2)*(s-side3));
    
    			printf( "Area of the Triangle is:\n%d\n", area);
    
    		}
    
    	else if ((side1 == side2) || (side1 == side3) || (side2 == side3))
    
    		{
    
    			printf( "Triangle is Isosceles\n" );
    
    			s = (side1 + side2 + side3)/2;
    
    			area=sqrt(s*(s-side1)*(s-side2)*(s-side3));
    
    			printf( "Area of the Triangle is:\n%d\n", area);
    
    		}
    
    		
    
    		printf( "Would you like to create another triangle? (Y/N)\n" );
    
    		scanf(  "%*", &buf);
    		scanf(  "%c", &user_input);
    
    
    		if ((user_input == 'y') || (user_input == 'Y'))
    
    		{
    
    			ok=1;
    
    		}
    
    		else if ((user_input == 'n') || (user_input == 'N'))
    
    		{
    
    			ok=0;
    
    		
    		}
    
    		else 
    			
    			printf ("Please enter either (Y/N)\n");
    		
    	}
    	while(ok == 1);
    
    printf( "Program has ended...\n" );
    
    return 0;
    
    }

  13. #13
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    Not sure of what you are expecting to get there, as you never allocated any space for buf. As for clearing the input buffer, have a look at this and this.

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