Error: ‘for’ loop initial declarations are only allowed in c99 mode.

Question

Problem :

I am very new to Programming. I have recently started learning C Programming. I have written below code but I am facing following error.

Please find below my source code for your reference:

#include <stdio.h>
void myfirstfunct(int[6]);
int main() 
{        
    int Arr[6]={1,2,3,4,5,6};
    myfirstfunct (Arr);
    for(int i=0;i<6;i++)
    printf("%d",Arr[i]);
}
void myfirstfunct(int p[6]) {
        int i,j;
        for(i=7,j=0;i<11;i++,j++)
            p[j]=i;
}

Please find below my error message for your reference:

hello.c: In function ‘main’:
hello.c:11:2: error: ‘for’ loop initial declarations are only allowed in C99 mode
for(inti=0;i<6;i++)
      ^
hello.c:11:2: note: use option -std=c99 or -std=gnu99 to compile your code`

I am looking for the very expert advice on quickly fixing above error.

Answer 1

You are very new to C programming so I am trying to help you. You are facing this error because of declaring the variables inside your for loop and it is not valid C programming until the C99. C99 is a standard of C which was published in 1999, you should either declare the counter outside your for loop or you can use a -std=c99 flag to tell your compiler explicitly that now you want to use this standard and so the compiler must interpret it correctly. 

You can also use a option -std=c99 for the compiler. You need to go to below path :

Project > Properties > C/C++ Buils > Settings > Tool Settings > GCC C Compiler > Dialect > Language Standard: Here you need to choose "ISO C99"

Hope you have understood the quick fix.

Answer 2

This occurs since declaring variables within a for loop wasn't valid C until C99(which is the standard of C published in 1999), you can either declare your counter outside the for as pointed out by others or employ the -std=c99 flag to inform the compiler apparently that you're employing this standard and it must interpret it as such.

You require to declare the variable j employed for the first for loop before the loop.

   int j;
    for(j=0;j<5;j++)
    printf("%d",Arr[j]);

I'd attempt to declare i outside of the loop!

#include <stdio.h>

int main() {

   int i;

   /* for loop execution */
   for (i = 10; i < 20; i++) {
       printf("i: %d\n", i);
   }   

   return 0;
}

There is a compiler switch which enables C99 mode, which amongst other things approves declaration of a variable within the for loop. To turn it on employ the compiler switch -std=c99

To switch to C99 mode in CodeBlocks, pursue 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've gotten this error too.

for (int i=0;i<10;i++) { ..

is not valid in the C89/C90 standard. As OysterD says, you require to do:

int i;
for (i=0;i<10;i++) { ..

in case you compile in C change

for (int i=0;i<10;i++) { ..

To

int i;
for (i=0;i<10;i++) { ..

You can further compile with the C99 switch set. Put -std=c99 in the compilation line:

gcc -std=c99 foo.c -o foo