Illegal use of floating point in C

Question

I kept getting Illegal use of character on the line that checks if a variable is empty or null.

Does anyone know why this happened?

the error points here:

if((fa == "" && fp == "") || (fb == "" && fp == "")){

though it worked before i just dont know whats causing this error.

Edit:

changed the code now the errors are too few parameters for function sinfa.

i only want to pass one parameter at a time to this function, is it possible or do i have to create another function to do that so that i can cater to them individually?

thank you. :)

#include<stdio.h>

#include<conio.h>
#include<math.h>
#define PI 3.14159265359

float sinfa(float num1,float num2)
{
    float fc;
    float powers;
    float rad_angle;

    if(num1 != 0){
    rad_angle = num1 * (PI / 180.0);
    powers = pow(rad_angle,4);
    fc = sin(rad_angle)-powers+1;
    }else{
    rad_angle = num2 * (PI / 180.0);
    powers = pow(rad_angle,4);
    fc = sin(rad_angle)-powers+1;
    }
    return (fc);
}

float sinp(float p1)
{
    float fop;
    float ppowers;
    printf("%f",p1);
    ppowers = pow(p1,4);
    fop = sin(p1)-ppowers+1;
    return (fop);
}

float tp(float fa,float fb,int num1,int num2)
{
    float p;
    float fm2 = fa*num2;
    float fm1 = fb*num1;
    p = fm2-fm1/fa-fb;
    return (p);
}

float main()
{
    float num1;
    float num2;
    float fa;
    float fb;
    float p1;
    float fp;

    clrscr();
    printf("Enter number 1: \n");
    scanf("%f", &num1);
    getch();
    printf("Enter number 2: \n");
    scanf("%f", &num2);
    getch();
    clrscr();

    if((fa == 0 && fp == 0) || (fb == 0 && fp == 0)){
        fa = sinfa(num1);
        fb = sinfa(num2);
        p1 = tp(fa,fb,num1,num2);
        fp = sinp(p1);
    }else{
        if((fa*fp) < 0){
            num1 = num1;
            num2 = p1;
            fa = sinfa(num1);
            fb = sinfa(num2);
            p1 = tp(fa,fb,num1,num2);
            fp = sinp(p1);
        }
        if((fb*fp)< 0){
            printf("\n 2");
            getch();
        }
    }
}

Answer 1

Error appears because you're comparing float with string literal, ie:

if((fa == "")

You can only do a comparison of float with a numeric/float literal, ie:

if((fa == 0.0

Recall that there's no such concept as NULL / uninitialized for primitive type such as float. Instead they typically default to 0.

Hence having the following means f value will be literal 0

float f;