CODEWITHSUNDEEP
c
demo
demo

Reputation: 7

bisection method program in c why do i need while before an if statement?

I'm new and trying to learn bisection method in c. Here is my program so far: 

 #include<stdio.h>
 #include<math.h>

 double f(double x)
 {
      return  pow(x,2)-2;
 }
 main()
 {
      double x1, x2, x3, i;
      do
      {
           printf("Enter a number for x1 and x2");
           scanf("%lf  %lf", &x1, &x2);
      }
      if(f(x1)*f(x2)<0);  /* **<--- if statement line 16** */

      for(i=0;i<100;i++)
      {
           x3=(x1+x2)/2;

           if (f(x1)*f(x3)<0)
               x2=x3;
           else
               x1=x3;

           if(f(x3)==0 || fabs(x1-x2)<0.000001) /* check if the roots*/
            break;

      }

      print("x=%lf \n",x3);
      return 0;
 }

and I got this error message. 

   16:error: expected âwhileâ before âifâ

I know my code is janky, but I'm still learning. I don't know why its expected to have a while loop before an if loop there.

Upvotes: 0

Views: 48

Answers (3)

dbush
dbush

Reputation: 223699

Right before the if, you have this:

  do
  {
       printf("Enter a number for x1 and x2");
       scanf("%lf  %lf", &x1, &x2);
  }
  if(f(x1)*f(x2)<0);

You have the start of a do...while loop, but there's no while condition. You also have an if with no statement that follows. You probably wanted to use while here instead of if:

  do
  {
       printf("Enter a number for x1 and x2");
       scanf("%lf  %lf", &x1, &x2);
  }
  while (f(x1)*f(x2)<0);

Upvotes: 1

selbie
selbie

Reputation: 104494

this:

if(f(x1)*f(x2)<0);  /* **<--- if statement line 16** */

should be:

while (f(x1)*f(x2)<0);  /* **<--- if statement line 16** */

Upvotes: 0

Acorn
Acorn

Reputation: 26066

Your do loop:

do {
    printf("Enter a number for x1 and x2");
    scanf("%lf  %lf", &x1, &x2);
}

is missing the closing while (...); condition.

Probably you wanted to write while instead of if.

Upvotes: 1

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