Coordinate Quadrant in C – Determine Quadrant I II III IV from (x,y)

The Cartesian coordinate plane is divided into four quadrants by the X and Y axes. Given a point (x, y), this program determines which quadrant it lies in — or whether it falls on an axis or at the origin. The logic is a direct translation of the mathematical definitions into C’s if-else chain.

Region	Condition	Example
Origin	x=0, y=0	(0, 0)
Y-axis	x=0, y≠0	(0, 5)
X-axis	x≠0, y=0	(3, 0)
Quadrant I	x>0, y>0	(3, 4)
Quadrant II	x<0, y>0	(−2, 5)
Quadrant III	x<0, y<0	(−1, −3)
Quadrant IV	x>0, y<0	(4, −2)

C Program: Coordinate Quadrant

/* Determine the quadrant of a Cartesian coordinate point (x, y)
 * Compile: gcc -ansi -Wall -Wextra quadrant.c -o quadrant */
#include <stdio.h>

int main(void)
{
    int x, y;
    printf("Enter x and y coordinates: ");
    if (scanf("%d %d", &x, &y) != 2) {
        printf("Invalid input.\n");
        return 1;
    }

    if (x == 0 && y == 0)
        printf("(%d, %d) is at the Origin.\n", x, y);
    else if (x == 0)
        printf("(%d, %d) is on the Y-axis.\n", x, y);
    else if (y == 0)
        printf("(%d, %d) is on the X-axis.\n", x, y);
    else if (x > 0 && y > 0)
        printf("(%d, %d) is in Quadrant I (x>0, y>0).\n",   x, y);
    else if (x < 0 && y > 0)
        printf("(%d, %d) is in Quadrant II (x<0, y>0).\n",  x, y);
    else if (x < 0 && y < 0)
        printf("(%d, %d) is in Quadrant III (x<0, y<0).\n", x, y);
    else
        printf("(%d, %d) is in Quadrant IV (x>0, y<0).\n",  x, y);

    return 0;
}

How to Compile and Run

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

Sample Output

Enter x and y coordinates: 3 4
(3, 4) is in Quadrant I (x>0, y>0).

Enter x and y coordinates: -2 5
(-2, 5) is in Quadrant II (x<0, y>0).

Enter x and y coordinates: 0 0
(0, 0) is at the Origin.

Enter x and y coordinates: 5 0
(5, 0) is on the X-axis.

Code Explanation

Check the special cases first — origin (x==0, y==0) is checked before x==0 alone, because the origin would also match “x==0” if that came first. Handling the more specific case (origin) before the more general one (on Y-axis) prevents incorrect output. This is the general principle: order if-else branches from most specific to most general.
The else case is always Quadrant IV — after ruling out origin, axes, and Quadrants I–III, the only remaining case is x>0, y<0. Using a final else without a condition is correct and slightly more efficient than writing else if (x > 0 && y < 0) — the compiler sees no additional condition to evaluate.
Integer vs floating-point coordinates — this program reads integers. For real-valued coordinates, change int x, y to double x, y and use scanf("%lf %lf", &x, &y). Floating-point comparison with exactly 0.0 can be unreliable for computed coordinates — use only for directly-entered user input.

What This Program Teaches

if-else chain ordering — each branch is checked only if all previous branches were false. Order from most specific to most general. The origin case must come before the Y-axis case because (0,0) satisfies both x==0 AND y==0 — only the first matching branch executes.
Using the final else as a catch-all — when you have exhaustively partitioned all cases and are sure the last one covers everything remaining, else without a condition is correct, readable, and avoids repeating the logical negation of all prior cases.
Real-world use — quadrant checks appear in game physics (which direction is a joystick pointing?), image processing (which region of a frame?), navigation (which bearing sector?), and collision detection (which side of an object did the projectile hit?).

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C Program to accept two integers for a co-ordinate point and determine its Quadrant.