C scanf in loop continues automaticly without input

Question

I'm trying to get input in an array, I expect input like the following.

5 (Number of the second dimensions in the array)
2 (Number of the first dimensions in the array)

So we get an array deeln[2][5] in this example. I try to get it with the following code:

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

bool isinarray(int val, int *arr, int size){
    int countimp;
    for (countimp=0; countimp < size; countimp++) {
        if (arr[countimp] == val)
            return true;
    }
    return false;
}


int main(void){

    int k, d, ci, cj, ck, ta;
    //get input
    scanf("%i", &k);
    scanf("%i", &d);

    int deeln[d][k], temp[k];

    for(ci = 0; ci < d; ci++){
        printf("d= %i, ci= %i \n", d, ci);
        scanf("%s", temp);
        for(cj = 0; cj < k; cj++){
            deeln[ci][cj] = temp[cj*2]-'0';
        }
    }

    //loop while. 
}

But i've got a problem, whenever i try to input, the program runs automaticly without getting any input when it loops around the third scanf for the 2nd or 3rd time. So then i'm not able to input anything.

What to do? Has it something to do with pointers or am i using scanf wrong?

UPDATE:

If I enter a printf after printf("cj is nu %i \n", cj); then the output also just came after the loop was going its own way. and not before i should give more input, using the third scanf.

But no, it doesn't work, I can stil not really input everything, when i enter at the beginning 2 and 5 i'm only able to input three times after that. — Genie Kort, Oct 13 '14 at 17:54
Are you hoping to scan `k+5` integers into the `temp` array? If yes, then you're gonna have to repeat that `k+5` times before using this array. — barak manos, Oct 13 '14 at 17:55
`temp[cj*2]-'0'` also looks like nonsense. you're gonna have to make up your mind as to what you want this `temp` to be. A null-terminated string, an array of characters (without the terminating null character), an array of integers, or simply a character that stores a single digit. — barak manos, Oct 13 '14 at 17:58
@barakmanos oh yea duh. sorry havent used c arrays for input in a while — jgr208, Oct 13 '14 at 17:59
my best guess is something is happening in your loop for checking the length. — jgr208, Oct 13 '14 at 18:01
@barak_manos, i will try to explain. I expect a given number of times input like the following: 1 2 3 4 5 and 2 1 4 3 5 and so on, with a random order of the numbers. I want to store every number in a different part of the array. So i have to skip a space character. And then, to convert the char of temp into an integer i have to do -'0' because the ascii value is then equal to the int value. — Genie Kort, Oct 13 '14 at 18:03
@GenieKort but it is good practice to internalize, if you don't and something gets out of wack you can end up with junk output — jgr208, Oct 13 '14 at 18:03
Ahaa, that's clear xd But why should i? Does it make a difference? — Genie Kort, Oct 13 '14 at 18:08
http://stackoverflow.com/questions/7786921/why-we-must-initialize-a-variable-before-using-it so you should also 0 out your array as well — jgr208, Oct 13 '14 at 18:10
One thing you should always do, is check return value of `scanf`. Otherwise you will end up debugging for (non-)bugs which are simply caused by accidental invalid input which you didn't handle. — hyde, Oct 13 '14 at 18:30
Maybe something interesting to know: if i try to printf k in the loop i get no value for k, k seems to be null.? — Genie Kort, Oct 13 '14 at 19:15
Its very strange, but every variable in the loop seems to be empty. — Genie Kort, Oct 13 '14 at 19:18

score 2 · Accepted Answer · answered Oct 13 '14 at 19:57

The solution of my question was quite easy. I found it after thinking of my input. The problem was that in the input, as described, there were spaces. Somehow scanf can't handle with spaces, unless you use some other syntax. But my solution is to just use fgets instead of scanf where I wanted to get the input. So the new and working code is as follows:

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

bool isinarray(int val, int *arr, int size){
    int countimp = 0;
    for (countimp=0; countimp < size; countimp++) {
        if (arr[countimp] == val)
            return true;
    }
    return false;
}


int main(void){


    int t, k = 0, d = 0, ci = 0, cj = 0, ta = 0;


    //get input
    scanf("%i", &k);
    scanf("%i", &d);
    char temp[20];
    int deeln[d][k];

    memset(deeln, 0 , sizeof(deeln));
    memset(temp, 0 , sizeof(temp));




    for(ci = 0; ci < d; ci++){
        fgets(temp, 20, stdin);
        for(cj = 0; cj < k; cj++){
            ta = cj*2;
            deeln[ci][cj] = temp[ta]-'0';
        }
    }

    //loop while. 
    return 1;
}

Thanks for helping everbody, even though we all didn't came to this. But I hope it will help others!

If this works for you, mark it as complete (hollow check mark above) By the way, what is `isinarray(...)` used for? — ryyker, Oct 13 '14 at 21:48
I can not do that, because it is my own answer. I have to wait for two days. — Genie Kort, Oct 14 '14 at 06:14
Oh - a rep thing. Well, +1 for persistence and finding the `fgets()` approach. Its a real improvement. — ryyker, Oct 14 '14 at 13:56
Rather than `fgets(temp, 20, stdin);`, consider `fgets(temp, sizeof temp, stdin);`. Easier to maintain code and more likely to be written correctly. — chux - Reinstate Monica, Sep 06 '15 at 22:11

ryyker · Answer 2 · 2023-07-18T13:44:54.497

Two places to look:

1)

cj = 0;//initialize cj before using here
scanf("%i", &temp[cj]);//temp is both an array, and an int.  Fix your format specifier,
                       //and use an index operator - temp[?] (not sure I am using the right index)

  deeln[ci][cj] = temp[cj*2]-'0'; //fix your logic here (array index will be exceeded)

An example of working code...

int main(void){

    int k, d, ci, cj, ck, ta;
    //get input, check values before allow code to continue
    if(scanf("%i", &k) != 1) {printf("scanf failed");return 0;} 
    if(scanf("%i", &d) != 1) {printf("scanf failed");return 0;} 

    int deeln[d][k], temp[k];

    for(ci = 0; ci < d; ci++){
        printf("d= %i, ci= %i \n", d, ci);
        for(cj = 0; cj < k; cj++){

            if(scanf("%i", &temp[cj]) != EOF)
            {
               deeln[ci][cj] = temp[cj]-'0'; 
            }
            else deeln[ci][cj] = -1;
        }
    }
    getchar();
    return 0;// main returns int, use  return statement
}

you can play with the index of temp[cj] to make it what you actually want, but I assume you are intending to read from stdin, then populate deeln[][] with that value, for each scanf.

If you want to parse a string containing spaces and digets, "1 3 8 5 3", you could use strtok() But your code as it is is not reading a string in, it is reading integers.

This is not perfect, you will have to do some debug, but will illustrate strtok(). You have to enter spaces between each digit after indices are selected: i.e.:

int main(void){

int k, d, ci, cj, ck, ta;

//get input, check values before allow code to continue
if(scanf("%i", &k) != 1) {printf("scanf failed");return 0;} 
if(scanf("%i", &d) != 1) {printf("scanf failed");return 0;} 
char inStr[d][k*5]; //space for up to k 3 digit numbers with 1 space each
char *buf=0;

int deeln[d][k], temp[k];

for(ci = 0; ci < d; ci++){
    printf("d= %i, ci= %i \n", d, ci);
    if(scanf("%s ", inStr[ci]) != EOF)
    {
        buf = strtok(inStr[ci], " ");
        cj = 0;
        while(buf && (cj < k))
        {
            deeln[ci][cj] = atoi(buf); 
            cj++;
        }
    }
}
//getchar();waits for user input, pauses execution
return 0; // main returns int, use  return statement

}

About 1. I already fixed that scanf, to %s. And i do not have to index those arrays do i? — Genie Kort, Oct 13 '14 at 18:24
See edit for fix that will allow code to run. Not sure it matches your requirements, but in short, you need to call `scanf` inside the inner loop — ryyker, Oct 13 '14 at 18:25
Missed that in your description, No, it will not. But if you enter the first two values for your array order, say 3, 3, Then enter the following 9 requests for integers, it will populate your deeln array. — ryyker, Oct 13 '14 at 18:29
I wouldn't say any code, which can easily lead to use of uninitialized variables, is "working code"... Please check return values of `scanf`, and only use the values parsed, if values were actually parsed successfully! — hyde, Oct 13 '14 at 18:31
@GenieKort - to parse a string containing digits and spaces into an array of variables, you could use char *buf = strtok(buf, " "); See edit. — ryyker, Oct 13 '14 at 18:40
Great thanks! But what I also would like to know is, how is it possible that scanf just doesn't work as expected? — Genie Kort, Oct 13 '14 at 19:07
scanf is seeing white space. Hitting the return key actually results in a \n or \n\r (windows, linux) either of which makes scanf() difficult to use for entering and parsing strings. Look at ***[sscanf()](http://stackoverflow.com/q/9578611/645128)*** (***[Or here](http://www.cplusplus.com/reference/cstdio/sscanf/)***) as an alternate. Hope the example gets you in the right direction. — ryyker, Oct 13 '14 at 19:16

C scanf in loop continues automaticly without input

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