#include <stdio.h>
#include <string.h>

int main()
{
    char input[100], output[100];
    gets(input);

    for(int i=0, a=0; i<strlen(input); a  )
    {
        char word = input[i];
        output[a] = word;
        if(word == 'a' || word == 'e' || word == 'i' || word == 'o' || word == 'u') i =3;
        else i =1;  
    }

    output[a] = '\0';    
    puts(output);
}

It says a is not declared, but didn't i declare it in the loop? How to declare a variable inside a loop without getting an error?

CodePudding user response：

Local scope :

In

for(int i=0, a=0; i<strlen(input); a  )

a goes out of scope, or is destroyed, once the loop exits.

From C11:

For such an object that does not have a variable length array type, its lifetime extends from entry into the block with which it is associated until execution of that block ends in any way.

Fix:

Declare a outside the loop.

Using gets():

The function gets() is inherently dangerous, and has been removed from the C standard. It provides no bounds checking and can potentially cause a buffer overflow. Instead, use fgets.

See: Why is the gets function so dangerous that it should not be used?

CodePudding user response：

You're getting that error because you're using a outside the body of the loop:

output[a] = '\0';    

a is only visible within the body of the for loop, and once the loop exits it no longer exists.

The easy way to deal with it is to declare a before the loop:

int a = 0;
for ( int i = 0; i < strlen( input ); a   )
  ...