How can I stop receiving input with a input in C

Question

I need to constantly get commands from the user and for that I wrote this:

scanf("%s %d %s %d", str1, &num1, str2, &num2);

The user should enter something like:

move 8 over 3

When the user type exit and enter, just this line, I must stop reading and print the result. The problem is, I have no idea how to do it. The context of the code:

do{
    scanf("%s %d %s %d", str1, &num1, str2, &num2); 

    do_stuff(vp, str1, str2, num1, num2, size);
}while (strncmp(str1, exit, 4)); // I used this but I must write (exit 1 exit 1) at least.

In strncmp() , exit is a string, with "exit", so comparing these four first characters I can stop the loop, but I necessarily need to type all four expected inputs.

Answer 1

As kaylum pointed out, it's better to use fgets in this case. That will give you the entire line at once, but more importantly, it allows you to set a maximum size. If scanf reads more input than can fit in the buffers, it will overwrite the buffers and that is dangerous.

char line[MAX_LINE]; // MAX_LINE should be a maximum input you define
while(fgets(line, sizeof line, stdin)) {
    char str1[MAX_LINE];
    char str2[MAX_LINE];

    if(strcmp(line, exit) == 0)
        break;

    // sscanf works like scanf, except it reads from a string
    // it is safer because you now have a string of a maximum size
    int r = sscanf(line, "%s %d %s %d", str1, &num1, str2, &num2);
    if(r == 4)
        do_stuff(vp, str1, str2, num1, num2);
    else
        puts("Wrong input format. Try again");
}

Answer 2

You can try this:

while ((scanf("%s", &str1) == 1) && strcmp(str1, "exit")) {
     scanf("%d %s %d", &num1, str2, &num2);

     do_stuff(vp, str1, str2, num1, num2, size);
}

I made this example code and it worked for me, basically this let us enter values for the four variables needed and stop the loop when strcmp(str1, "exit") == 0 , notice that 4 values are being entered in two scanf(), I do not know what implications it may have for the buffer.

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

void do_stuff(char *str1, char *str2, int num1, int num2) {
    printf("     entered: %s %d %s %d\n", str1, num1, str2, num2);
}

int main() {

    char str1[100], str2[100];
    int num1 = 0, num2 = 0;

    while ((scanf("%99s", &str1) == 1) && strcmp(str1, "exit")) {
        scanf("%d %99s %d", &num1, str2, &num2);

        do_stuff(str1, str2, num1, num2);
    }
    printf("     loop finish!");

    return 0;
}

Command line:

move 8 over 3
     entered: move 8 over 3
move 4 over 2
     entered: move 4 over 2
exit
     loop finish!