Using math.h Library Functions in C

Algorithm

1. Read a decimal number x.
2. Print sqrt(x), pow(x, 3), ceil(x), floor(x) and fabs(-x).
3. Print each result on its own line with two decimal places.

C program

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

int main(void) {
    double x;

    printf("Enter a number:\n");
    if (scanf("%lf", &x) != 1) {
        printf("Error: invalid input\n");
        return 1;
    }

    printf("sqrt(x)   = %.2f\n", sqrt(x));
    printf("pow(x, 3) = %.2f\n", pow(x, 3));
    printf("ceil(x)   = %.2f\n", ceil(x));
    printf("floor(x)  = %.2f\n", floor(x));
    printf("fabs(-x)  = %.2f\n", fabs(-x));
    return 0;
}

Sample input and output

2.4

Enter a number:
sqrt(x)   = 1.55
pow(x, 3) = 13.82
ceil(x)   = 3.00
floor(x)  = 2.00
fabs(-x)  = 2.40

0

Enter a number:
sqrt(x)   = 0.00
pow(x, 3) = 0.00
ceil(x)   = 0.00
floor(x)  = 0.00
fabs(-x)  = 0.00

How the program works

Each function in math.h works on doubles. The square root of a negative number is a domain error that returns NaN, so this demo uses a non-negative value to keep the output meaningful.

ceil rounds up and floor rounds down toward the nearest whole number, which is the difference you should be able to explain in the viva.

Viva questions

Common mistakes

• Forgetting to include math.h, which makes sqrt implicitly declared.
• Expecting ^ to be a power operator; pow is the function to use.