Pass variables to function : Function Parameter « Function « C Tutorial

#include <stdio.h>

float average(float x, float y)
  return (x + y)/2.0f;

int main(void)
  float value1 = 1.0F;
  float value2 = 2.0F;
  float value3 = 0.0F;

  value3 = average(value1, value2);
  printf("\nThe average is: %f\n",  value3);
  return 0;
The average is: 1.500000

8.5.Function Parameter
8.5.1.Parameter passing
8.5.2.Call by reference
8.5.3.Pass variables to function
8.5.4.Use pointer as function parameter
8.5.5.Cube a variable using call-by-value
8.5.6.Cube a variable using call-by-reference with a pointer argument