Thread: Overlooking something in a comparison

I am trying to compare the input from the user to whether they entered something or not. If they did not, move onto the next input. I know I am missing something. I tried several ways of comparing:
strcmp, this =="NULL" this = "NULL", etc. What am I missing. Here is my code:

Code:

case 3:
            fread(data, sizeof(sched_record), MAX_RECORD, filePointer);
            fclose(filePointer);
            printf("Enter Dept Name: ");
              scanf("%s", tempDept);
            printf("Enter Course Number of 0 for any course in department: ");
              scanf("%d", &tempCourse);
            printf("Enter Days of Class, M for MW, T for TTH or D for any: ");
              scanf("%s", tempDay);
            printf("Enter A for mornings, P for afternoons of D for any: ");
              scanf("%s", tempTime);
            for (i=0; i < MAX_RECORD; i++) {
                if (tempDept == "NULL"){
                    if (strcmp(tempDept, data[i].Dept)==0) {
                        printf("\n%s", data[i].Dept);
                    }
                }

                else if (tempCourse != '0'){
                    if (tempCourse = data[i].course){
                    printf("\n%d", data[i].course);
                    }
                }
            }

        break;

Originally Posted by stahta01

The easiest thing to do is record the value returned by scanf call.
scanf - C++ Reference

Next easiest is shown in code segment below

Code:

/* set to known value before scanf */
tempDept[0]='\0'  /* set tempDept value to a C Nul string */

/* after scanf test for known value */
if(tempDept[0]=='\0')

Tim S.

I tried this:

Code:

printf("Enter Dept Name: ");
            tempDept[0]='\0';
            scanf("%s", tempDept);
            if (tempDept[0]=='\0');
            printf("Enter Course Number of 0 for any course in department: ");
            scanf("%d", &tempCourse);

and does not seem to work. Even tried it like:

Code:

printf("Enter Dept Name: ");
            tempDept[0]='\0';
            scanf("%s", tempDept);
            if (tempDept[0]=='\0') {
            printf("Enter Course Number of 0 for any course in department: ");
            }
            scanf("%d", &tempCourse);

This is a scheduling program with many constraints, hence if no department is chosen, move onto course.
tempDept is an array, not a pointer.

Originally Posted by whiteflags

You'll have to use a completely different scanf I think. Something like this...

Code:

#include <stdio.h>
int main()
{
   int i;
   char text[BUFSIZ];
   char* inputs[] = { "stuff\n", "", "\n", "more stuff\n" };
   for (i = 0; i < sizeof inputs / sizeof *inputs; i++) {
      int result = sscanf(inputs[i], "%[^\n]", text);
      if (result == 1) {
         printf("good: text=\"%s\"\n", text);
      }
      else {
         printf("bad: input=\"%s\"\n", inputs[i]);
      }
   }
   return 0;
}

/* output:
good: text="stuff"
bad: input=""
bad: input="
"
good: text="more stuff"
*/

C code - 17 lines - codepad

If you actually use sscanf like I did though, %s will probably work. scanf does a blocking read from the keyboard, which means it will wait as long as it can to read something. Unlike something defined as a string, if scanf stopped reading input just because the user hit return too soon, it could miss whatever input is coming. Compare that to a string: if you run out of string before the whole format string is used, the input is obviously wrong.



Other idea... You could also instruct the user to send EOF in this situation. But you would have to use the return result of scanf to know what happened. But then, return values from input functions are always important!

Thanks!