Where are the mistakes in my own sqrt() function?

Learning C for a couple of days, wanted to write a code to find the square root of a number by Newton's method.

#include <stdio.h>
#include <stdlib.h>

int truncate (double num)             //rounds float to integer
{
    if (num < 0) {
            return (num + 0.5);
    }
    else {
        return (num - 0.5);
    }
}

double sqr(double num){              //square function
    return num * num;
}

double sqrt(double number) {         //root function
    double guess, quotient, average;

    guess = 1.0;

    do {
        quotient = number / guess;
        printf("%f\t", quotient);
        average = (guess + quotient) / 2.0;
        printf("%f\n", average);
        guess = average;
    } while ((abs(number - sqr(guess))) > 0.001);

    return guess;
}

int main(){
    float a;

    scanf("%f", a);

    printf("%.2f", sqrt(a));

}

What are the mistakes? Error: Process returned -1073741819 (0xC0000005) execution time : 2.371 s

You should pass a double to the function, instead, in main, you're passing a float.

just change float a; to double a;

Also, in main, you have to write scanf("%lf",&a); instead of scanf("%lf",a);. That's the only way you'll calculate on the right number you pass your program.