C PROGRAMMING PROGRAM • FUNCTIONS, PREPROCESSOR & COMMAND LINE

Build a Calculator Using Function Pointers

Learn how to build a calculator using function pointers using a clear C program.

AdvancedFunction pointerCallbackIndirect call

PROBLEM UNDERSTANDING

Input and expected output

Sample input

1
14 9

Sample output

Result = 23

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>
#include <stddef.h>

int add(int first, int second) { return first + second; }
int subtract(int first, int second) { return first - second; }

int main(void)
{
    int choice, first, second;
    int (*operation)(int, int) = NULL;
    printf("1. Add  2. Subtract: ");
    scanf("%d", &choice);
    printf("Enter two integers: ");
    scanf("%d %d", &first, &second);
    if (choice == 1) operation = add;
    else if (choice == 2) operation = subtract;
    else { puts("Invalid choice."); return 0; }
    printf("Result = %d\n", operation(first, second));
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Result = 23

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Store the selected function's address in a compatible pointer and invoke it indirectly.
Display the computed result.

Store the selected function's address in a compatible pointer and invoke it indirectly.

EFFICIENCY

Time and space complexity

Time complexity

O(1)

Auxiliary space

O(1)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

Check this

Initialize variables before using their values.

Check this

Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.