As we all know, before using a variable we need to declare it. Similarly, before using a function we need to declare the function. This declaration of the function is called as function prototyping. Consider the below program. float fnGetAverage(int, int); void main() { int x,y; float z; printf(“\nEnter the values for x and y”); scanf(“%d %d”, &x, &y); z = fnGetAverage(x, y); //function call printf(“\nThe average is %d”, z); } float fnGetAverage(int a, int b) { //function definition float c; c = (a+b)/2; //calculating average return c; //returning the value } There is one statement before the main() function....