I got: "expected ';', ',' or ')' before '&' token "in C

Question

Why does &x1 cannot be accpeted

int calculte (float a, float b, float c, float &x1, float &x2)

I'm trying to solve quadratic equation, here's my full program

    #include<stdio.h>
    #include<math.h>
    int calculte  (float a, float b, float c, float &x1, float &x2){
        float delta = b*b -4*a*c;
        if (delta <0) {
            x1 =x2 = 0.0;
            return 0;
        } if (delta == 0) {
            x1 = x2 = -b/(2*a);
            return 1;
        } if (delta >0) {
            delta = sqrt(delta);
            x1 = (-b-delta)/(2*a);
            x2 = (-b - delta)/(2*a);
            return 2;
        }
    }
    int main () {
        float a, b, c, x1, x2;
        do {
            scanf ("%f %f %f", &a, &b, &c);
        }
        while (!a);
        int ans = calculte (a,b,c,x1,x2);
        if (ans==0) {
            printf ("NO");
        } 
        if (ans==1){
            printf ("%.2f",x1);
        }
        if (ans==2) {
            printf ("%.2f %.2f", x1, x2);
        }
    }

I am new to programming, so hope you guys can explain me more details.

Answer 1

You cannot use references in C.

Instead of that, you should make the arguments to pointers by changing & to *.

Also the function body and calling have to be changed according to that.

#include<stdio.h>
#include<math.h>
int calculte  (float a, float b, float c, float *x1, float *x2){ /* change the arguments to pointers */
    float delta = b*b -4*a*c;
    if (delta <0) {
        *x1 =*x2 = 0.0; /* dereference the pointers */
        return 0;
    } if (delta == 0) {
        *x1 = *x2 = -b/(2*a); /* dereference the pointers */
        return 1;
    } if (delta >0) {
        delta = sqrt(delta);
        *x1 = (-b-delta)/(2*a); /* dereference the pointer */
        *x2 = (-b - delta)/(2*a); /* dereference the pointer */
        return 2;
    }
}
int main () {
    float a, b, c, x1, x2;
    do {
        scanf ("%f %f %f", &a, &b, &c);
    }
    while (!a);
    int ans = calculte (a,b,c,&x1,&x2); /* add & to get the pointers */
    if (ans==0) {
        printf ("NO");
    } 
    if (ans==1){
        printf ("%.2f",x1);
    }
    if (ans==2) {
        printf ("%.2f %.2f", x1, x2);
    }
}