/* * File: reverse.c * --------------- * This program reads in an array of integers, reverses the * elements of the array, and then display the elements in * their reversed order. */#include <stdio.h>#include "genlib.h"#include "simpio.h"/* * Constants * --------- * MaxElements -- Maximum number of elements * Sentinel    -- Value used to terminate input */#define MaxElements 250#define Sentinel      0/* Private function prototypes */static int GetIntegerArray(int array[], int max, int sentinel);static void PrintIntegerArray(int array[], int n);static void ReverseIntegerArray(int array[], int n);static void SwapIntegerElements(int array[], int p1, int p2);static void GiveInstructions(void);/* Main program */main(){    int list[MaxElements], n;    GiveInstructions();    n = GetIntegerArray(list, MaxElements, Sentinel);    ReverseIntegerArray(list, n);    PrintIntegerArray(list, n);}/* * Function: GetIntegerArray * Usage: n = GetIntegerArray(array, max, sentinel); * ------------------------------------------------- * This function reads elements into an integer array by * reading values, one per line, from the keyboard.  The end * of the input data is indicated by the parameter sentinel. * The caller is responsible for declaring the array and * passing it as a parameter, along with its allocated * size.  The value returned is the number of elements * actually entered and therefore gives the effective size * of the array, which is typically less than the allocated * size given by max.  If the user types in more than max * elements, GetIntegerArray generates an error. */static int GetIntegerArray(int array[], int max, int sentinel){    int n, value;    n = 0;    while (TRUE) {        printf(" ? ");        value = GetInteger();        if (value == sentinel) break;        if (n == max) Error("Too many input items for array");        array[n] = value;        n++;    }    return (n);}/* * Function: PrintIntegerArray * Usage: PrintIntegerArray(array, n); * ----------------------------------- * This function displays the first n values in array, * one per line, on the console. */static void PrintIntegerArray(int array[], int n){    int i;    for (i = 0; i < n; i++) {        printf("%d\n", array[i]);    }}/* * Function: ReverseIntegerArray * Usage: ReverseIntegerArray(array, n); * ------------------------------------- * This function reverses the elements of array, which has n as * its effective size.  The procedure operates by going through * the first half of the array and swapping each element with * its counterpart at the end of the array. */static void ReverseIntegerArray(int array[], int n){    int i;    for (i = 0; i < n / 2; i++) {        SwapIntegerElements(array, i, n - i - 1);    }}/* * Function: SwapIntegerElements * Usage: SwapIntegerElements(array, p1, p2); * ------------------------------------------ * This function swaps the elements in array at index * positions p1 and p2. */static void SwapIntegerElements(int array[], int p1, int p2){    int tmp;    tmp = array[p1];    array[p1] = array[p2];    array[p2] = tmp;}/* * Function: GiveInstructions * Usage: GiveInstructions(); * -------------------------- * This function gives instructions for the array reversal program. */static void GiveInstructions(void){    printf("Enter numbers, one per line, ending with the\n");    printf("sentinel value %d.  The program will then\n", Sentinel);    printf("display those values in reverse order.\n");}