How do I fix for loop initial declaration used outside C99 mode GCC error

Question

I m trying to solve the 3n 1 problem and I have a for loop that looks like this    for int i   low  i  lt   high    i                            res   runalg i                   if  res  gt  highestres                                            highestres   res                                 Unfortunately I m getting this error when I try to compile with GCC      3np1 c 15  error   for  loop initial   declaration used outside C99 mode   I don t know what C99 mode is  Any ideas

User · Answer

For anyone attempting to compile code from an external source that uses an automated build utility such as Make, to avoid having to track down the explicit gcc compilation calls you can set an environment variable. Enter on command prompt or put in .bashrc (or .bash_profile on Mac):

export CFLAGS="-std=c99"

Note that a similar solution applies if you run into a similar scenario with C++ compilation that requires C++ 11, you can use:

export CXXFLAGS="-std=c++11"

User · Answer

I ve gotten this error too   for  int i 0 i lt 10 i           is not valid in the C89 C90 standard  As OysterD says  you need to do   int i  for  i 0 i lt 10 i           Your original code is allowed in C99 and later standards of the C language

User · Answer

Jihene Stambouli answered OP question most directly    Question was  why does  for int i   low  i  lt   high    i        res   runalg i       if  res  gt  highestres                highestres   res            produce the error   3np1 c 15  error   for  loop initial declaration used outside C99 mode   for which the answer is   for int i   low      should be  int i  for  i low

User · Answer

I d try to declare i outside of the loop   Good luck on solving 3n 1  -   Here s an example     include  lt stdio h gt   int main         int i         for loop execution       for  i   10  i  lt  20  i             printf  i   d n   i               return 0      Read more on for loops in C here

User · Answer

if you compile in C change  for  int i 0 i lt 10 i           to  int i  for  i 0 i lt 10 i           You can also compile with the C99 switch set  Put -std c99 in the compilation line   gcc -std c99 foo c -o foo   REF  http   cplusplus syntaxerrors info index php title  for  loop initial declaration used outside C99 mode

User · Answer

I had the same problem and it works you just have to declare the i outside of the loop     int i   for i   low  i  lt   high    i             res   runalg i           if  res  gt  highestres                            highestres   res

User · Answer

For Qt-creator  just add next lines to   pro file     QMAKE CFLAGS DEBUG         -std gnu99  QMAKE CFLAGS RELEASE         -std gnu99

User · Answer

There is a compiler switch which enables C99 mode  which amongst other things allows declaration of a variable inside the for loop  To turn it on use the compiler switch -std c99  Or as  OysterD says  declare the variable outside the loop

User · Answer

To switch to C99 mode in CodeBlocks  follow the next steps   Click Project Build options  then in tab Compiler Settings choose subtab Other options  and place -std c99 in the text area  and click Ok   This will turn C99 mode on for your Compiler   I hope this will help someone

User · Answer

Blorgbeard   New Features in C99   inline functions variable declaration no longer restricted to file scope or the start of a compound statement several new data types  including long long int  optional extended integer types  an explicit boolean data type  and a complex type to represent complex numbers variable-length arrays support for one-line comments beginning with     as in BCPL or C   new library functions  such as snprintf new header files  such as stdbool h and inttypes h type-generic math functions  tgmath h  improved support for IEEE floating point designated initializers compound literals support for variadic macros  macros of variable arity  restrict qualification to allow more aggressive code optimization   http   en wikipedia org wiki C99  A Tour of C99

User · Answer

Enable C99 mode in Code  Blocks 16 01   Go to Settings-  Compiler    In Compiler Flags section of Compiler settings tab  select checkbox  Have gcc follow the 1999 ISO C language standard  -std c99

[c] How do I fix "for loop initial declaration used outside C99 mode" GCC error?

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