Pointer to Function in C++

1#include <iostream>
2#include <vector>
3#include <algorithm>
4#include <string>
5using namespace std;
6
7// Basic arithmetic functions
8int add(int a, int b) {
9    return a + b;
10}
11
12int subtract(int a, int b) {
13    return a - b;
14}
15
16int multiply(int a, int b) {
17    return a * b;
18}
19
20int divide(int a, int b) {
21    if (b != 0) {
22        return a / b;
23    }
24    return 0;
25}
26
27// Function with different signature
28void greet(string name) {
29    cout << "Hello, " << name << "!" << endl;
30}
31
32// Function that takes function pointer as parameter (callback)
33void performOperation(int a, int b, int (*op)(int, int), string opName) {
34    cout << a << " " << opName << " " << b << " = " << op(a, b) << endl;
35}
36
37// Function that returns a function pointer
38int (*getOperation(char op))(int, int) {
39    switch(op) {
40        case '+': return add;
41        case '-': return subtract;
42        case '*': return multiply;
43        case '/': return divide;
44        default: return nullptr;
45    }
46}
47
48int main() {
49    cout << "=== BASIC FUNCTION POINTER USAGE ===" << endl;
50    
51    // Declare function pointer: returnType (*pointerName)(parameters)
52    int (*operation)(int, int);
53    
54    int num1 = 20, num2 = 5;
55    
56    // Point to add function
57    operation = add;
58    cout << num1 << " + " << num2 << " = " << operation(num1, num2) << endl;
59    
60    // Point to subtract function
61    operation = subtract;
62    cout << num1 << " - " << num2 << " = " << operation(num1, num2) << endl;
63    
64    // Point to multiply function
65    operation = multiply;
66    cout << num1 << " * " << num2 << " = " << operation(num1, num2) << endl;
67    
68    // Point to divide function
69    operation = divide;
70    cout << num1 << " / " << num2 << " = " << operation(num1, num2) << endl;
71    
72    cout << "
73=== ARRAY OF FUNCTION POINTERS ===" << endl;
74    // Array of function pointers
75    int (*operations[])(int, int) = {add, subtract, multiply, divide};
76    char opSymbols[] = {'+', '-', '*', '/'};
77    
78    for (int i = 0; i < 4; i++) {
79        cout << num1 << " " << opSymbols[i] << " " << num2 
80             << " = " << operations[i](num1, num2) << endl;
81    }
82    
83    cout << "
84=== USING TYPEDEF FOR READABILITY ===" << endl;
85    // Using typedef to make function pointer syntax cleaner
86    typedef int (*MathOp)(int, int);
87    MathOp op1 = add;
88    MathOp op2 = multiply;
89    cout << "Using typedef: " << op1(10, 5) << " and " << op2(10, 5) << endl;
90    
91    cout << "
92=== CALLBACK FUNCTION EXAMPLE ===" << endl;
93    // Passing function pointer as parameter (callback)
94    performOperation(15, 3, add, "+");
95    performOperation(15, 3, subtract, "-");
96    performOperation(15, 3, multiply, "*");
97    performOperation(15, 3, divide, "/");
98    
99    cout << "
100=== FUNCTION POINTER FROM FUNCTION ===" << endl;
101    // Getting function pointer from another function
102    int (*selectedOp)(int, int) = getOperation('+');
103    if (selectedOp != nullptr) {
104        cout << "Result from getOperation('+'): " << selectedOp(8, 4) << endl;
105    }
106    
107    cout << "
108=== FUNCTION POINTER WITH STL ===" << endl;
109    // Using function pointer with STL algorithms
110    vector<int> numbers = {5, 2, 8, 1, 9, 3};
111    cout << "Original: ";
112    for (int n : numbers) cout << n << " ";
113    
114    // Sort using function pointer
115    bool (*compare)(int, int) = [](int a, int b) { return a > b; };
116    sort(numbers.begin(), numbers.end(), compare);
117    
118    cout << "
119Sorted (descending): ";
120    for (int n : numbers) cout << n << " ";
121    cout << endl;
122    
123    cout << "
124=== NULL POINTER CHECK ===" << endl;
125    // Checking for null function pointer
126    int (*nullOp)(int, int) = nullptr;
127    if (nullOp == nullptr) {
128        cout << "Function pointer is null (safe to check)" << endl;
129    }
130    
131    return 0;
132}