C Function Parameters: Passing Information to Functions

Learn how to pass information to functions in C using parameters. These parameters function as variables within the function and are defined inside the parentheses following the function name. Discover how to specify multiple parameters by separating them with commas, allowing for flexible and efficient function design in your C programming projects.

C Function Parameters

Parameters and Arguments

In C, you can pass information to functions through parameters. These parameters act like variables inside the function. Parameters are specified inside the parentheses after the function name, and you can add multiple parameters by separating them with commas.

Syntax

returnType functionName(parameter1, parameter2, parameter3) {
  // code to be executed
}

Example: Passing Parameters

In the example below, the function accepts a string of characters as a parameter. When the function is called, we pass along a name, which the function uses to print "Hello" along with each person's name:

void myFunction(char name[]) {
  printf("Hello %s\n", name);
}

int main() {
  myFunction("Alice");
  myFunction("Bob");
  myFunction("Claire");
  return 0;
}

Hello Alice
Hello Bob
Hello Claire

Multiple Parameters

Inside the function, you can include multiple parameters. Here’s an example:

void myFunction(char name[], int age) {
  printf("Hello %s. You are %d years old.\n", name, age);
}

int main() {
  myFunction("Alice", 25);
  myFunction("Bob", 30);
  myFunction("Claire", 20);
  return 0;
}

Hello Alice. You are 25 years old.
Hello Bob. You are 30 years old.
Hello Claire. You are 20 years old.

Passing Arrays as Parameters

You can also pass arrays to a function. The function will loop through the array elements:

void myFunction(int myNumbers[5]) {
  for (int i = 0; i < 5; i++) {
    printf("%d\n", myNumbers[i]);
  }
}

int main() {
  int myNumbers[5] = {10, 20, 30, 40, 50};
  myFunction(myNumbers);
  return 0;
}

10
20
30
40
50

Return Values in C Functions

In C, you can also return values from a function. For this, use a data type (like int or float) instead of void. The function returns a value using the return keyword:

int myFunction(int x) {
  return 5 + x;
}

int main() {
  printf("Result is: %d", myFunction(7));
  return 0;
}

Result is: 12

Store Return Values in Variables

You can store the result of a function in a variable:

int myFunction(int x, int y) {
  return x + y;
}

int main() {
  int result = myFunction(6, 4);
  printf("Result is = %d", result);
  return 0;
}

Result is = 10

Practical Example: Convert Fahrenheit to Celsius

Here is a practical example that uses a function to convert a temperature from Fahrenheit to Celsius:

float toCelsius(float fahrenheit) {
  return (5.0 / 9.0) * (fahrenheit - 32.0);
}

int main() {
  float f_value = 104.2;
  float result = toCelsius(f_value);

  printf("Fahrenheit: %.2f\n", f_value);
  printf("Convert Fahrenheit to Celsius: %.2f\n", result);

  return 0;
}

Fahrenheit: 104.20
Convert Fahrenheit to Celsius: 40.11