Finding Local maximum in C

Question

I would like to find the local maximum within the interval of 0 to 3.1416 for this Sin(x) function. But it shows always 0 as the maximum value.i.e The maximum value=0; Please help me finding my faults.

thanks.

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
#ifndef max
    #define max(a,b) ((a)>(b)?(a):(b))
#endif
double f(double x){
return sin(x);
}
double bisection(double a,double b)
{
double Fa=f(a);
double Fb=f(b);
double midpoint=(a+b)/2;
double Fmidpoint=f(midpoint);
while(abs(b-a)>1e-6){
double left=(a+midpoint)/2;
double right=(b+midpoint)/2;
double Fleft=f(left);
double Fright=f(right);
if(midpoint>max(Fleft,Fright)){
    a=left;
    Fa=Fleft;
    b=right;
    Fb=Fright;
}
else{
    if(Fleft>Fright)
    {
        b=midpoint;
        Fb=Fmidpoint;
        midpoint=left;
        Fmidpoint=Fleft;
    }
    else{
        a=midpoint;
        Fa=Fmidpoint;
        midpoint=right;
        Fmidpoint=Fright;
    }
}
}
return midpoint;
}
int main(){
double maximum;
double rangeleft=0;
double rangeright=3.1416;
maximum=bisection(rangeleft,rangeright);
printf("%d",maximum);
return 0;
}

Answer 1

You have an error in calling the printf function.

You should not use %d format identifier here because it means that printf should output an integer while your maximum variable is double.

Use %f instead and your program will output 1.5708 which is correct.

You can find the list of all possible printf format identifiers on Wikipedia.