How to Pass Arguments to Function in C: Simple Guide

In C, you pass arguments to a function by listing them inside the parentheses in the function call, matching the parameters defined in the function declaration. Use type name pairs in the function definition to specify what kind of arguments the function expects.

Syntax

The basic syntax to pass arguments to a function in C involves defining the function with parameters and then calling it with matching arguments.

• Function definition: Specify the types and names of parameters inside parentheses.
• Function call: Provide values (arguments) in the same order as parameters.

c

return_type function_name(type1 param1, type2 param2, ...) {
    // function body
}

// Calling the function
function_name(arg1, arg2, ...);

Example

This example shows a function add that takes two integers as arguments and returns their sum. The main function calls add with two numbers.

c

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int main() {
    int result = add(5, 3);
    printf("Sum is %d\n", result);
    return 0;
}

Output

Sum is 8

Common Pitfalls

Common mistakes when passing arguments include:

• Passing arguments in the wrong order, which can cause unexpected results.
• Not matching the number or types of arguments with the function parameters.
• Forgetting to declare the function prototype before calling it, leading to compiler warnings or errors.

Always ensure the function declaration and call agree on argument types and order.

c

#include <stdio.h>

// Wrong: calling function with arguments in wrong order
int subtract(int a, int b) {
    return a - b;
}

int main() {
    int result = subtract(5); // Error: missing argument
    printf("Result: %d\n", result);
    return 0;
}

// Correct way:
// int result = subtract(5, 3);

Quick Reference

Tips for passing arguments in C functions:

• Match the number and types of arguments to parameters.
• Use meaningful parameter names for clarity.
• Pass by value copies the argument; to modify original data, use pointers.
• Declare function prototypes before use to avoid errors.

Key Takeaways

Define function parameters with types to specify expected arguments.

Pass arguments in the same order and type as parameters when calling a function.

Mismatch in argument count or type causes errors or unexpected behavior.

Use function prototypes before calls to ensure correct argument passing.

To modify variables inside functions, pass pointers instead of values.