Callback function demonstration Dry Run in C

Callback function demonstration is an interactive C dry run visualizer from the Pointersfunctions programs section. Study the source code, then use the execution controls to follow each step, variable update, highlighted line, and console output.

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Callback function demonstration Program Code

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

// Callback function types
typedef void (*ProcessCallback)(int item, int index);
typedef int (*FilterCallback)(int item);
typedef void (*TimerCallback)(void);

// Process array with callback for each element
void processArray(int *arr, int size, ProcessCallback callback) {
    int i;
    for(i = 0; i < size; i++) {
        callback(arr[i], i);
    }
}

// Filter array using callback to decide which elements to keep
int* filterArray(int *arr, int size, FilterCallback filter, int *newSize) {
    int i;
    int *result = malloc(size * sizeof(int));
    *newSize = 0;
    for(i = 0; i < size; i++) {
        if(filter(arr[i])) {
            result[(*newSize)++] = arr[i];
        }
    }
    return result;
}

// Different callback implementations
void printItem(int item, int index) {
    printf("arr[%d] = %d\n", index, item);
}

void printSquare(int item, int index) {
    printf("arr[%d]^2 = %d\n", index, item * item);
}

void printEvenOnly(int item, int index) {
    if(item % 2 == 0) {
        printf("arr[%d] = %d (even)\n", index, item);
    }
}

int isEven(int item) {
    return item % 2 == 0;
}

int isGreaterThan5(int item) {
    return item > 5;
}

// Timer simulation using callback
void setTimer(int seconds, TimerCallback callback) {
    printf("Timer set for %d seconds...\n", seconds);
    printf("Simulating wait...\n");
    callback();      // Fire the callback
}

void alarmCallback() {
    printf("*** ALARM! Time's up! ***\n");
}

int main() {
    int i;
    int numbers[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
    int size = 10;
    int filteredSize;
    int *evens;
    int *greater;
    
    printf("=== Callback Examples ===\n\n");
    
    printf("1. Print each element:\n");
    processArray(numbers, size, printItem);
    
    printf("\n2. Print squares:\n");
    processArray(numbers, size, printSquare);
    
    printf("\n3. Print even numbers only:\n");
    processArray(numbers, size, printEvenOnly);
    
    printf("\n4. Filter even numbers:\n");
    evens = filterArray(numbers, size, isEven, &filteredSize);
    printf("Even numbers: ");
    for(i = 0; i < filteredSize; i++) {
        printf("%d ", evens[i]);
    }
    printf("\n");
    free(evens);
    
    printf("\n5. Filter numbers >5:\n");
    greater = filterArray(numbers, size, isGreaterThan5, &filteredSize);
    printf("Numbers >5: ");
    for(i = 0; i < filteredSize; i++) {
        printf("%d ", greater[i]);
    }
    printf("\n");
    free(greater);
    
    printf("\n6. Timer callback (simulated):\n");
    // setTimer(3, alarmCallback);  // Would wait 3 seconds
    
    return 0;
}

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