Surface Area and Volume of a Cube in C

A cube is a three-dimensional shape with six equal square faces. Given the side length s, the surface area is 6s² (six faces, each with area s²) and the volume is s³. This program reads the side length and computes both values using only basic arithmetic — no need for pow() and the -lm flag when the exponent is a small integer.

The original post used void main(), pow(side, 3) (requiring -lm), and broken \n. This rewrite uses side * side * side instead of pow(), which avoids the math library dependency and is more efficient for integer exponents.

Cube Formulas

Property	Formula	Side = 5
Surface area	6 × s²	6 × 25 = 150
Volume	s³	5 × 5 × 5 = 125
Diagonal (face)	s√2	5 × 1.4142 ≈ 7.071
Diagonal (space)	s√3	5 × 1.7321 ≈ 8.660

C Program: Surface Area and Volume of a Cube

/* Surface area and volume of a cube
 * Surface area = 6 * s^2
 * Volume = s^3
 * Compile: gcc -ansi -Wall -Wextra cube.c -o cube */
#include <stdio.h>

int main(void)
{
    double side, surface_area, volume;

    printf("Enter the length of a side: ");
    if (scanf("%lf", &side) != 1 || side <= 0.0) {
        printf("Error: side must be a positive number.\n");
        return 1;
    }

    surface_area = 6.0 * side * side;
    volume       = side * side * side;

    printf("Side          = %.4f\n", side);
    printf("Surface area  = %.4f  (6 * %.4f^2)\n", surface_area, side);
    printf("Volume        = %.4f  (%.4f^3)\n", volume, side);
    return 0;
}

How to Compile and Run

gcc -ansi -Wall -Wextra cube.c -o cube
./cube

Sample Output

Enter the length of a side: 5
Side          = 5.0000
Surface area  = 150.0000  (6 * 5.0000^2)
Volume        = 125.0000  (5.0000^3)

Enter the length of a side: 2.5
Side          = 2.5000
Surface area  = 37.5000  (6 * 2.5000^2)
Volume        = 15.6250  (2.5000^3)

Code Explanation

side * side * side instead of pow(side, 3) — pow() is a general-purpose floating-point power function from <math.h> that requires linking with -lm. For small integer exponents like 2 and 3, direct multiplication is faster, requires no library, and compiles without -lm. Reserve pow() for non-integer or large exponents (e.g., pow(x, 1.5)).
double instead of float — double provides about 15–16 significant decimal digits of precision. float provides only 6–7. For geometric calculations where inputs might be large (e.g., a side of 1000 meters), float’s limited precision causes visible rounding errors. double is the default floating-point type in C and is almost always preferable.
scanf("%lf", &side) not scanf("%f") — when reading into a double with scanf, you must use %lf (long float). Using %f with a double pointer reads only 4 bytes (float-sized) and leaves the remaining 4 bytes of the double uninitialized — a silent bug. printf uses %f for both float and double (it promotes float to double), but scanf does not.
Validation: side <= 0.0 — a cube with side zero or negative is geometrically meaningless. Checking this before computing prevents outputting negative or zero areas and volumes that would confuse the user.

What This Program Teaches

When not to use pow() — for s², s³, s⁴: use multiplication. pow(x, 2) may be slower than x * x because pow() handles fractional exponents and special cases (NaN, infinity). Some compilers optimize pow(x, 2.0) to x * x automatically, but it is clearer to write the multiplication directly.
%f vs %lf in scanf — this scanf vs printf asymmetry trips up many beginners. Always use %lf in scanf for double, %f for float. In printf, %f works for both (default argument promotion converts float to double). The asymmetry is a consequence of how variadic functions work in C.
Surface area and volume scale differently — doubling the side doubles each edge, but surface area scales by 4× (2² = 4) and volume scales by 8× (2³ = 8). This is the square-cube law: relevant in physics, biology (why ants can lift many times their body weight but elephants cannot) and engineering.

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C Program to compute the surface area and volume of a cube