---
title: 6.15 Explicit Function Declarations
description: "An explicit function declaration specifies a function's return type and parameter types before the function is called. This allows the compiler to check whether function calls use a compatible interface. ``` #include int divide(int numerator, int denominator); int main(void) {…"
url: "https://edcret.in/docs/c-programming/c-functions/6-15-explicit-function-declarations/"
updated: "2026-10-27"
category: C Programming / Functions
---

# 6.15 Explicit Function Declarations

An explicit function declaration specifies a function's return type and parameter types before the function is called. This allows the compiler to check whether function calls use a compatible interface.

```
#include <stdio.h>

int divide(int numerator, int denominator);

int main(void)
{
    int result = divide(20, 4);

    printf("Result = %dn", result);

    return 0;
}

int divide(int numerator, int denominator)
{
    return numerator / denominator;
}
```

### Example Output

```
Result = 5
```

### Explanation

The declaration:

```
int divide(int numerator, int denominator);
```

specifies that `divide()` returns an `int` and accepts two `int` parameters. It appears before the function call, so the compiler knows the function's interface when processing the call.

The definition provides the implementation:

```
int divide(int numerator, int denominator)
{
    return numerator / denominator;
}
```

The function call supplies two arguments:

```
divide(20, 4);
```

The function divides `20` by `4` and returns `5`.

### Explicit Declaration Forms

| Declaration | Meaning |
| --- | --- |
| `int getValue(void);` | Returns `int` and accepts no parameters |
| `double calculate(double, double);` | Returns `double` and accepts two `double` arguments |
| `void display(const char *message);` | Returns no value and accepts a pointer to constant characters |
| `int compare(int a, int b);` | Returns `int` and accepts two integer arguments |

An explicit function declaration is also called a **function prototype** when it specifies the parameter types. In modern C, declaring functions before use is standard practice, especially when declarations are shared through header files.