Remove the last comma from c loop-CodePudding

i have the belowo loop in c that print the prime number

  for(int i = 2; i<=arraySize; i  )
    {
        //If arraySize is not 0 then it is prime
       if (numbers[i]!=0)
        printf("%d,",numbers[i]);
      
    }

the out put after enter 50 for example is 2,3,5,7,11,13,17,19,23,29,31,37,41,43,47, i want to to not print the last comma how i can do it

i tried this code but not working

printf("%d%s", numbers[i], (i !=arraySize-1) ? "," : "");

CodePudding user response：

Instead of printing a comma after each number, print it before. Then you can use a variable to tell if this is the first number being printed, and not print the comma.

first=true;

for(int i = 2; i<=arraySize; i  )
{
    //If numbers[i] is not 0 then it is prime
    if (numbers[i]!=0) {
        printf("%s%d", (first ? "" : ","), numbers[i]);
        first = false;
    }  
}

CodePudding user response：

I like both the other answers but just want to throw in this error prone variant on the same theme.

_Bool first = true;

for (int i = 2; i <= arraySize; i  ) {
    if (numbers[i] != 0) {
        printf(",%d"   first, numbers[i]);
        first = false;
    }
}

If first is true the actual formatting string will become "%d". If it's false it'll become ",%d".

CodePudding user response：

Simple: Use a pointer to the "prefix" string, printed AHEAD of the next value:

char *sep = "";
for(int i = 2; i <= arraySize; i   ) {
    if( numbers[i] ) {
        printf( "%s%d", sep, numbers[i] );
        sep = ", "; // I added a SP, too
    }
}

Here's an alternative that uses a "limited scope" variable to index a static string. For clarity in this example, the array boundaries have been adjusted.

int main( void ) {
    int numbers[] = { 1, 1, 4, 8, 9, 0, 7 };
    int arraySize = sizeof numbers/sizeof numbers[0];

    for( int i = 0, out = 0; i < arraySize; i   )
        if( numbers[i] )
            printf("%s%d", &","[!out  ], numbers[i] );

    return 0;
}

The negated boolean post-incrementing value of out provides the address of the '\0' to the first instance, then the address of "," in subsequent instances.

1,1,4,8,9,7

CodePudding user response：

The answers already here are fine, but I'd like to add a "simpler" solution. Simpler in that it doesn't require any further logic or extra variables. It does, however, require that you know that the first number is non-zero.

printf("%d", numbers[2]);
for (int i = 3; i < arraySize; i  )
{
    if (numbers[i] != 0)
        printf(",%d", numbers[i]);
}

CodePudding user response：

I think the other answers overcomplicates things. I don't see any reason to have a test for every iteration in the loop. Instead, I'd simply do the special case first:

printf("%d", numbers[2]);

for (int i = 3; i <= arraySize; i  ) {
    if (numbers[i]!=0) 
        printf(",%d", numbers[i]);
}

This will however need some additional code to correctly handle the case where arraySize is lower than 3.

But I would choose another approach from the beginning, and that is writing a good function for printing an array. Could look like this:

void printArray(const int *array, int size) {
    putchar('['); // Of course this is optional

    if(size > 0) {
        printf("%d", array[0]);

        for(int i=0; i<size; i  )
            printf(",%d", array[0]);
    }

    putchar(']'); // And this too
}

and then something like this:

int convertArray(const int *numbers, int *array, int size) {
    int ret = 0;

    for(int i=0; i<size; i  ) {
        if(number[i] != 0) {
            array[ret] = numbers[i];
            ret  ;
        }
    }

    return ret;
}