C scanf() problem

3
votes

Im new to C and cant for the life of me work out what im doing wrong here. The first scanf works fine, variables are printed out as they are read in. The second scanf doesn't seem to be reading the input correctly. Input is of the format "char int int" i.e. b 4 4
when i print opb x and y out, opb = " ", x = 13238272 , y=0. Any Ideas?.....note ive cut out code below the problem

int main(void)
{

/*initialize variables*/
int width, height;
char op;

/*grid input*/
scanf("%c %d %d", &op, &width, &height);

/*check conditions*/
if (op != 'g' || width>100 || height>100 || width*height<10 || width<1 || height<1) {
    printf("grid-error\n");
    return 0;
}

/*initialize grid elements*/
int grid[width][height];
char printGrid[width][height];

/*create grid elements*/
int i, j;
for (i=0; i<height; i++) {
    for (j=0; j<width; j++) {
        grid[j][i] = 0;
        printGrid[j][i] = '*';
    }
}

/*print successful creation*/
printf("%c %d %d \n", op, width, height);

int k;
for (k = 0; k<10; k++) {
    /*initialize variables*/
    int x, y;
    char opb;

    /*mine input*/
    scanf("%c %d %d", &opb, &x, &y);

    /*check conditions*/
    if (opb != 'b' || x<0 || y<0 || x>(width-1) || y>(height-1) || grid[x][y] == 9) {
        printf("mine-error\n");
        return 0;
    }
2
cscanf
You should check the return value of scanf(), because it's the only way you'll know if there's a format error. – geekosaur
yer appears theres a format error (as it didnt return 3), whats going on here? – Milk
@user445559: One thing that occurs to me right off is that %c will read the next available character — even if it's a space or the newline left over from reading the previous line. In general it's safer to read input as lines and use sscanf() to parse them. – geekosaur
the only problem is weve been instructed to use scanf. So im just manually catching bad input – Milk
Not to sound like a grumpy old geekosaur or anything, but if that's what they're teaching these days.... – geekosaur

2 Answers

4
votes

I suspect the problem is that you aren't dealing with newline characters in your input. The result is that the opb is actually a newline character (not a space, though it looks like one) and x and y aren't read at all (i.e. they retain the values they were initialised with).

To solve the problem, try adding the newline to both your scanfs. That is:

scanf("%c %d %d\n", &op, &width, &height);

and later

scanf("%c %d %d\n", &opb, &x, &y);
0
votes

I think the easiest would be to put space before %c in second scanf. If you use it without space, it will take first symbol. That means, newline. The space makes %c take first symbol that isn't space or tab. So:

scanf(" %c %d %d", &op, &x, &y);