（C代码）我将如何在函数之间传递我的全局变量并在主函数也需要它们时返回它们？我在下面发布了我的代码以供参考。当然，我也有一个头文件，其中也包含我的函数原型，但它们只在右括号内列出变量类型，而不是变量名......
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include "myheader.h"
char user_filename[150];
char user_filename2[150];
FILE *fp;
FILE *fp2;
int num_shift;
int main()
{
int choice; // main variables
int option;
char result;
char ch;
int offset;
char character;
int tmp;
option = 0;
num_shift = 0;
strncpy(user_filename, "not set", sizeof("not set"));
strncpy(user_filename2, "not set", sizeof("not set"));
fp = NULL;
fp2 = NULL;
choice = menu(num_shift, user_filename, option); // get user's first selection
while(choice != QUIT) //execute so long as choice is not equal to QUIT
{
switch(choice)
{
case INPUT_FILE:
input(user_filename);
break;
case OUTPUT_FILE:
output();
break;
case NUM_TO_SHIFT:
num_shift = shift(num_shift);
printf ("Shift by %d\n",num_shift);
break;
case ENCODE:
encode(result, ch, num_shift, character);
break;
case QUIT:
quit();
break;
case REVIEW:
review (user_filename);
break;
default:
printf("Oops! An invalid choice slipped through. ");
printf("Please try again.\n");
}
choice = menu(num_shift, user_filename, 0); /* get user's subsequent selections */
}
quit();
}
int menu(int num_shift, char * user_filename, int option)
{
printf("\nText Encoder Service\n\n");
printf("1.\tEnter name of input file (currently '%s')\n", user_filename);
printf("2.\tEnter name of output file (currently '%s')\n", user_filename2);
printf("3.\tEnter number of characters data should be shifted (currently %d)\n", num_shift);
printf("4.\tEncode the text\n");
printf("5.\tReview the text in the input file\n");
printf("\n0.\tQuit\n\n");
printf("Make your selection: \n");
while( (scanf(" %d", &option) != 1) /* non-numeric input */
|| (option < 0) /* number too small */
|| (option > 5)) /* number too large */
{
fflush(stdin); /* clear bad data from buffer */
printf("That selection isn't valid. Please try again.\n\n");
printf("Your choice? ");
}
printf("Selecting %d\n\n", option);
return option;
}
int input(char * user_filename)
{
printf("Enter the filename of the file to encode:\n");
printf("(hit the Enter key when done)\n");
scanf("%s", user_filename);
printf("Getting %s\n\n", user_filename);
fp = fopen (user_filename, "r");
if (fp == NULL)
{
printf("\nSorry, I'm unable to open the file (%s) for reading\n", user_filename);
printf("Please try again.\n");
}
else
{
fclose(fp);
}
return INPUT_FILE;
}
int output()
{
printf("Enter the filename of the output file to store encoded information:\n");
printf("(hit the Enter key when done)\n");
scanf("%s", user_filename2);
printf("Opening File for Writing %s\n\n", user_filename2);
fp2 = fopen (user_filename2, "w");
if (fp2 == NULL)
{
printf("\nSorry, I'm unable to open the file (%s) for writing\n", user_filename2);
printf("Please try again.\n");
} else
{
fclose(fp2);
}
//return user_filename;
return INPUT_FILE;
}
int shift(int num_shift)
{
printf("Enter the number of letters to shift for each character: \n");
printf("(hit the Enter key when done)\n");
scanf("%d", &num_shift);
printf("Setting shift value to: %d\n\n", num_shift);
return num_shift;
}
int encode(char result, char ch, int offset, char character2)
{
int character;
printf("starting encoding with offset of %d\n", offset);
fp = fopen(user_filename, "r");
fp2 = fopen(user_filename2, "w+bc");
if ((fp == NULL) || (fp2 == NULL))
{
printf ("File not found\n");
return (0);
}
fseek(fp, 0, SEEK_SET);
printf("staring Encoding from %s to %s at position %ld\n", user_filename, user_filename2, ftell(fp));
int i = 0;
while(character = fgetc(fp))
{
if ( character == EOF)
{
//printf("%c",character);
//fprintf(fp2,"%c",result);
fclose(fp);
fflush(fp2);
fclose(fp2);
return(0);
}
if (isalpha (character))
{
if (character >= 'a' && character <= 'z')
{
result = character - 'a';
result = (result + offset) % 26; // 26 letters in the alphabet
result += 'a';
if (result < 'a')
{
result = 'z' - ('a' - result)+1;
}
} else if (character >= 'A' && character <= 'Z')
{
result = character - 'A';
result = (result + offset) % 26; // 26 letters in the alphabet
result += 'A';
if (result < 'A')
{
result = 'Z' - ('A' - result)+1;
}
}
//printf("(%c)",result);
} else
{
result = character;
//printf("(%x)", result);
}
printf("%c",result);
fprintf(fp2,"%c",result);
}
return 0;
}
void quit()
{
//fclose(fp);
//fclose(fp2);
printf("Quiting...Bye!");
printf("\n");
exit(0);
}
int review(char * user_filename)
{
char character;
fp = fopen(user_filename, "r");
printf("Showing text from %s file\n", user_filename);
printf("----------BEGIN OF TEXT--------------\n");
while(character = fgetc(fp))
{
if ( character == EOF)
{
printf("%c",character);
printf("\n----------END OF TEXT--------------\n");
fclose(fp);
return(0);
}
printf("%c",character);
}
}