ISO C90 forbids mixed declarations and code in C

Question

I declared a variable in this way   int i   0    I get the warning       ISO C90 forbids mixed declarations and code   How can I fix it

User · Answer

Just use a compiler  or provide it with the arguments it needs  such that it compiles for a more recent version of the C standard  C99 or C11  E g for the GCC family of compilers that would be -std c99

User · Answer

Up until the C99 standard  all declarations had to come before any statements in a block   void foo       int i  j    double k    char  c        code    if  c          int m  n          more code          etc      C99 allowed for mixing declarations and statements  like C      Many compilers still default to C89  and some compilers  such as Microsoft s  don t support C99 at all     So  you will need to do the following    Determine if your compiler supports C99 or later  if it does  configure it so that it s compiling C99 instead of C89  If your compiler doesn t support C99 or later  you will either need to find a different compiler that does support it  or rewrite your code so that all declarations come before any statements within the block

User · Answer

Make sure the variable is on the top part of the block  and in case you compile it with -ansi-pedantic  make sure it looks like this   function         int i      i   0       someCode

User · Answer

I think you should move the variable declaration to top of block  I e         foo        int i   0      bar        to        int i   0      foo        bar

User · Answer

To diagnose what really triggers the error  I would first try to remove   0   If the error is tripped  then most likely the declaration goes after the code  If no error  then it may be related to a C-standard enforcement compile flags OR    something else    In any case  declare the variable in the beginning of the current scope  You may then initialize it separately  Indeed  if this variable deserves its own scope - delimit its definition in      If the OP could clarify the context  then a more directed response would follow

User · Answer

-Wdeclaration-after-statement minimal reproducible example  main c     usr bin env bash  set -eux  cat  lt  lt  EOF  gt  main c  include  lt stdio h gt   int main void        puts  hello        int a   1      printf   d n   a       return 0    EOF   Give warning   gcc -std c89 -Wdeclaration-after-statement -Werror main c gcc -std c99 -Wdeclaration-after-statement -Werror main c gcc -std c89 -pedantic -Werror main c   Don t give warning   gcc -std c89 -pedantic -Wno-declaration-after-statement -Werror main c gcc -std c89 -Wno-declaration-after-statement -Werror main c gcc -std c99 -pedantic -Werror main c gcc -std c89 -Wall -Wextra -Werror main c   https   stackoverflow com questions 14737104 what-is-the-default-c-mode-for-the-current-gcc-especially-on-ubuntu 53063656 53063656 gcc -pedantic -Werror main c   The warning   main c  In function    main     main c 5 5  warning  ISO C90 forbids mixed declarations and code  -Wdeclaration-after-statement       int a   1             Tested on Ubuntu 16 04  GCC 6 4 0

[c] ISO C90 forbids mixed declarations and code in C

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