Finding characters within a string in C

Question

I'm writing an algorithm in C with netbeans to find asterisks in a string.

int main() {
    int M=0, i, j;
    scanf("%i",&M);
    int pos[M];
    char c[M];
    scanf("%s", c);

    i=0;
    j=1;

    while(c[i] != '\0'){
        if(c[i]=='*'){
            pos[j] = i;
            j++;
        }
        i++;
    }

    printf("Asterisks in positions: \n\n");

    for(j=1; j<=i; j++){
        printf("%i", pos[j]);
    }
    return 0;
}

But it doesn't work, it prints a lot of numbers even if M is a small number.

You did not ask a question. StackOverflow is a place to get questions answered. — abelenky
– abelenky, Commented Nov 30, 2010 at 4:24
What input are you giving your program? What output are you getting? What output do you expect? — abelenky
– abelenky, Commented Nov 30, 2010 at 4:24

salezica · Accepted Answer · 2010-11-30 04:23:59Z

2

The problem seems to be you never take into account the number of characters found. You print the whole vector, using i instead of j to iterate. It's j that holds the number of matches.

Also, try using strchr, from cstring :)

Get the first position, then search again from the next character until null is returned.

answered Nov 30, 2010 at 4:23

salezica

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1 Comment

Jonathan Leffler Over a year ago

Or strcspn() which returns a count of the characters skipped.

Commodore63 · Accepted Answer · 2010-11-30 04:31:12Z

1

The information regarding how many asterisks you found is stored in the counter j. This variable gets reset in the for loop:

for(j=1; j<=i; j++)

Furthermore, this for loop goes all the way up to i, which is the length of the your input string. Try reworking your loop as follows:

for(i=1; i<j; i++){    
    printf("%i", pos[i]);    
}

answered Nov 30, 2010 at 4:31

Commodore63

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Comments

casablanca · Accepted Answer · 2010-11-30 04:25:14Z

0

After your while loop completes, j holds the total number of positions recorded, so you should be printing from pos[1] to pos[j]. Your current loop prints from pos[1] to pos[i]. Just invert the variables in your final loop:

for(i=1; i<=j; i++){
    printf("%i", pos[i]);
}

answered Nov 30, 2010 at 4:25

casablanca

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