Thread: need help with an if else loop

im writing this code and i cant get the if else part to work, and posts that might help would be greatly appreciated
thanks

Code:

#include<stdio.h>
#include<math.h>
main()
{
#include<stdio.h>
#include<math.h>
main()
{
int x, y;
double A, B, C;
printf("Enter (double ) A, B, C:\n");
scanf("%f %f %f", A, B, C);
printf("Enter (double) x:\n");
scanf("%f", x);
{
if (x <=0)
        y= (A*x*x + B);
        printf("Case 1\nx value is = %d and y value is = %d", x, y);
else{
        if (x <<1)
                y= (B + C*x);
                printf("Case 2\nx value is = %d and y value is = %d", x, y);
        else{
        (x >=1)
                y= (B + C);
        printf("Case 3\nx value is = %d and y value is = %d", x, y);
}
}
}
exit(0) ;
}

these are the errors i get:

Code:

q4.c:15: parse error before "else"
q4.c:19: parse error before "else"
q4.c: At top level:
q4.c:25: parse error before '}' token
q4.c:26: parse error before numeric constant
q4.c:26: warning: data definition has no type or storage class

this was my assignment if it helps:

Code:

/*

              MAE9: Homeworki #4, Spring 2003

          Due on Thursday, May 1, before 11:00 pm


A mathematical relationship between x and y is described by
the following expressions:

y= A*x^2 + B  if  x<=0   (Case 1)

y=B+C*x       if  0<x<1  (Case 2)

y=B+C         if  x>=1   (Case 3)

where A, B, and C are constants. Write a C program that reads
the double values of the constants A,B,C, and the argument x
(by using scanf), and computes the corresponding value of y.
Print x and y by using %f format with 3 decimal places.

Use the pow(a,b) function to calculate x^2, and if/else
statements to choose the proper expression for y, corresponding
to selected x.

After reading A,B,C, your program should use a for loop to
evaluate y for scanned x in each of the above three cases.

Your output should look like:


Enter (double ) A, B, C:
1. 2. 3.

Enter (double) x:
0.5
Case 2
x value is = 0.500  and  y value is = 3.500

Enter (double) x:
-1.
Case 1
x value is = -1.000  and  y value is = 3.000

Enter (double) x:
2.
Case 3
x value is = 2.000  and  y value is = 5.000


.......................................................

Note: If you started working on hw4 before Friday, and
made the output as below, it's acceptible. If you didn't,
try to get above output.

Enter (double ) A, B, C:
1. 2. 3.

Case 1
Enter (double) x:
-1.
x value is = -1.000  and  y value is = 3.000

Case 2
Enter (double) x:
0.5
x value is = 0.500  and  y value is = 3.500

Case 3
Enter (double) x:
2.
x value is = 2.000  and  y value is = 5.000

*/

thanks for any help

you were right i added in the brackets and its actually compiling now, but it core dumps every time i put in numbers. heres what i have now:

Code:

#include<stdio.h>
#include<math.h>
main()
{
int x, y;
double A, B, C;
printf("Enter (double ) A, B, C:\n");
scanf("%f %f %f", A, B, C);
printf("Enter (double) x:\n");
scanf("%f", x);
{
if (x <=0)
        {
        y= (A*x*x + B);
        printf("Case 1\nx value is = %d and y value is = %d", x, y);
        }
else{
        if (x <<1)
        {
                y= (B + C*x);
                printf("Case 2\nx value is = %d and y value is = %d", x, y);
        }
        else{
                y= (B + C);
        printf("Case 3\nx value is = %d and y value is = %d", x, y);
}
}
}
exit(0) ;
}

thanks for helping me out

Thanks, the & worked for the A B and C when i put in numbers for them this is what I got:

Code:

iacs5.ucsd.edu 34: a.out
Enter (double) A, B, C:
1. 2. 3.
Enter (double) x:
Case 1
x value is = 0 and y value is = 0iacs5.ucsd.edu 35: vi q4.c

something is wrong with my x, its not asking for a value, its just running the rest of the program.
thanks for the feedback

im sorry i dont understand what youre saying i have to do, this is the first class ive ever taken in programming and about as new to it as you can get ummm, i tried writing a second program using the same begining but with a do while loop instead of the if else's but it never prints the part asking for the value of x and then the equations are all off below, if you think i was closer in the first code than this one ill go back to it, im just trying to get something to go through. so here it is:

Code:

#include<stdio.h>
#include<math.h>
main()
{
{
int y;
double A, B, C, x;
printf("Enter (double) A, B, C:\n");
scanf("%d %d %d", &A, &B, &C);

printf("Enter (double) x:\n");
scanf("%d", &x);

do
{
 y= (A*x*x + B);
 printf("Case 1\nx value is = %d and y value is = %d\n", x, y);
break;
}
while (x <= 0);
do
{
 y= (B + C*x);
 printf("Case 2\nx value is = %d and y value is = %d\n", x, y);
break;
}
while (0 < x & x > 1);
do
{
 y= (B + C);
 printf("Case 3\nx value is = %d and y value is = %d\n", x, y);
break;
}
while (1 <= x);
}
exit(0);
}

and heres what i get

Code:

Enter (double) A, B, C:
1. 2. 3. 
Enter (double) x:
Case 1
x value is = 8 and y value is = 0
Case 2
x value is = 130 and y value is = 0
Case 3
x value is = 130 and y value is = 0

Oh, sorry, I didn't know you where a real newbie. Ok, try to compile and run this source code:

Code:

#include<stdio.h>

void tidy(FILE *);

void tidy(FILE *in)
{
	int c;
	
	while((c = fgetc(in)) != EOF && c != '\n');
}

int main()
{
	int x, y;
	double A, B, C;
	printf("Enter (double) A, B, C:\n");
	//%lf instead %f because A, B, C are of type double
	scanf("%lf %lf %lf", &A, &B, &C);
	printf("Enter (int) x:\n");
	tidy(stdin);
	//%d instead %f because x is of type int
	scanf("%d", &x);
	
	if (x <=0)
	{
		y= A*x*x + B;
		printf("Case 1\nx value is = %d and y value is = %d", x, y);
	}
	else
	{
	    if (x <<1)
	    {
	        y= B + C*x;
	        printf("Case 2\nx value is = %d and y value is = %d", x, y);
	    }
	    else
	    {
	    	y= B + C;
	    	printf("Case 3\nx value is = %d and y value is = %d", x, y);
		}
	}
	
	return 0;
}

I will go to bed now. I hope somebody else will help you during the next hours if you should need further assistance.

I compiled it and it works, the x's are off but im sure thats my equations, thanks so much for your help, I really appreciate it.

You should read again Salem's first post! He already pointed out what's wrong.
Just take a book on C programming and read about if ... else and >, >=, ==, <=, < and left/right shift operators ( <<, >> ).