CodeXRay

In CodeXRay: Open the Preprocessing stage: UNIVERSITY and YEAR are replaced by their values, and stdio.h is pulled in.

/*
 * Hello World with macros
 * Look at the Preprocessing stage: the #define names are replaced by their values.
 */
#include <stdio.h>

#define UNIVERSITY "GVPIHLR"
#define YEAR 2026

int main(void) {
    printf("Hello World!\n");
    printf("Welcome to %s, batch of %d.\n", UNIVERSITY, YEAR);
    return 0;
}

Hello World!
Welcome to GVPIHLR, batch of 2026.

In CodeXRay: Switch to Call Stack & Memory: main() calls area(), which calls square().

/*
 * Functions
 * Look at Call Stack & Memory: main() calls area(), which calls square().
 */
#include <stdio.h>

int square(int n) {
    return n * n;
}

int area(int side) {
    return square(side);
}

int main(void) {
    int side = 7;
    int a = area(side);

    printf("Side of the square = %d\n", side);
    printf("Area of the square = %d\n", a);
    return 0;
}

Side of the square = 7
Area of the square = 49

In CodeXRay: Switch to Call Stack & Memory: factorial() calls itself, so the stack grows and then shrinks.

/*
 * Recursion: factorial
 * Look at Call Stack & Memory: factorial() calls itself, so the stack grows and then shrinks.
 */
#include <stdio.h>

int factorial(int n) {
    if (n <= 1) {
        return 1;
    }
    return n * factorial(n - 1);
}

int main(void) {
    int i;

    for (i = 1; i <= 5; i++) {
        printf("%d! = %d\n", i, factorial(i));
    }
    return 0;
}

1! = 1
2! = 2
3! = 6
4! = 24
5! = 120

In CodeXRay: Open the Assembly stage: the for loop becomes compare and jump instructions.

/*
 * Arrays and loops
 * Look at the Assembly stage to see how a for loop becomes compare-and-jump instructions.
 */
#include <stdio.h>

int main(void) {
    int marks[5] = {78, 92, 65, 88, 71};
    int i, sum = 0, max = marks[0];

    for (i = 0; i < 5; i++) {
        sum += marks[i];
        if (marks[i] > max) {
            max = marks[i];
        }
    }

    printf("Total   = %d\n", sum);
    printf("Average = %.2f\n", sum / 5.0);
    printf("Highest = %d\n", max);
    return 0;
}

Total   = 394
Average = 78.80
Highest = 92

In CodeXRay: Switch to Call Stack & Memory: swap() receives the addresses of x and y, so it changes main()'s variables.

/*
 * Pointers: swap two numbers
 * Look at Call Stack & Memory: swap() gets the addresses of x and y, so it changes main()'s variables.
 */
#include <stdio.h>

void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

int main(void) {
    int x = 10, y = 20;

    printf("Before swap: x = %d, y = %d\n", x, y);
    swap(&x, &y);
    printf("After swap:  x = %d, y = %d\n", x, y);
    return 0;
}

Before swap: x = 10, y = 20
After swap:  x = 20, y = 10

In CodeXRay: Open the LLVM IR stage: the struct becomes a type with an int, a char array and an int array.

/*
 * Structures
 * A struct groups related values (roll number, name, marks) under one name.
 */
#include <stdio.h>

struct Student {
    int roll;
    char name[20];
    int marks[3];
};

int main(void) {
    struct Student s = {101, "Asha", {85, 90, 78}};
    int i, total = 0;

    for (i = 0; i < 3; i++) {
        total += s.marks[i];
    }

    printf("Roll    : %d\n", s.roll);
    printf("Name    : %s\n", s.name);
    printf("Total   : %d\n", total);
    printf("Average : %.2f\n", total / 3.0);
    return 0;
}

Roll    : 101
Name    : Asha
Total   : 253
Average : 84.33

In CodeXRay: Open the Preprocessing stage: SQUARE(4) becomes ((4) * (4)) and the DEBUG line is removed.

/*
 * Macros and conditional compilation
 * Look at the Preprocessing stage: the #ifdef DEBUG line disappears because DEBUG is not defined,
 * and SQUARE(4) is expanded to ((4) * (4)).
 */
#include <stdio.h>

#define SQUARE(x) ((x) * (x))
#define MAX(a, b) ((a) > (b) ? (a) : (b))

int main(void) {
    printf("SQUARE(4)    = %d\n", SQUARE(4));
    printf("SQUARE(2+3)  = %d\n", SQUARE(2 + 3));
    printf("MAX(15, 9)   = %d\n", MAX(15, 9));

#ifdef DEBUG
    printf("Debug mode is ON\n");
#else
    printf("Debug mode is OFF\n");
#endif
    return 0;
}

SQUARE(4)    = 16
SQUARE(2+3)  = 25
MAX(15, 9)   = 15
Debug mode is OFF