ISO C90错误：声明

Question

首先，我要说这个标准是必需的，也是我目前必须使用的标准。

无论如何，我遇到一个错误，并尝试将我的FILE *块移动到main的内部/外部，可执行文件等之前。

#include <stdio.h>
#include <stdlib.h>

/* Initialize vars */
char c1, c2, c3, c4, c5, c6, c7, c8, c9, c10, c11, c12;

int main()
{

    /* Open encrypted.txt for reading */
FILE *enc;
enc = fopen("encrypted.txt", "r");

    /* Retrieve individual characters, displace by 4 letters (decryption method) */
c1 = (getc(enc))-4;
c2 = (getc(enc))-4;
c3 = (getc(enc))-4;
c4 = (getc(enc))-4;
c5 = (getc(enc))-4;
c6 = (getc(enc))-4;
c7 = (getc(enc))-4;
c8 = (getc(enc))-4;
c9 = (getc(enc))-4;
c10 = (getc(enc))-4;
c11 = (getc(enc))-4;
c12 = (getc(enc))-4;

    /* Display resulting decrypted message */
printf("%c%c%c%c%c%c%c%c%c%c%c%c", (char)c1, (char)c2, (char)c3, (char)c4, (char)c5, (char)c6, (char)c7, (char)c8, (char)c9, (char)c10, (char)c11, (char)c12);

    /* Write decrypted message to new file named "decrypted" */
FILE *dec;
dec = fopen("decrypted", "w");

fprintf(dec,"%c%c%c%c%c%c%c%c%c%c%c%c", (char)c1, (char)c2, (char)c3, (char)c4, (char)c5, (char)c6, (char)c7, (char)c8, (char)c9, (char)c10, (char)c11, (char)c12);

    /* Close files */
fclose(enc);
fclose(dec);

}

任何有关如何摆脱这个错误的提示，不胜感激！ 提前致谢

Answer 1

C90不允许在块中的其他语句之后声明变量，因此您需要在声明enc的顶部和顶部声明dec：

int main()
{

    /* Open encrypted.txt for reading */
   FILE *enc, *dec;
   ...
}

Answer 2

在C99中，您可以在其他语句之后并在for循环中声明。 但不是在C90中

如果使用gcc，请使用-std = c99选项来避免此错误。

 gcc -std=c99 -Wall source.c 

要么

移动FILE *dec; 到FILE *enc;的下方FILE *enc;

像这样

 FILE *enc;
 FILE *dec;