Thread: If statments for a struct w/ strings

Hello all! Trying to finish up my last programming assignment for the semester. In the beginning of the program I created a struct, and one of the individual elements of the struct is a character string called "action". What I want to do is IF action is ____, then do this. I'm getting all sorts of compiler errors. I'm only going to post the code from the function I wrote it in, but if you want to see the struct or main, let me know.

Code:

int readfile(FILE *ifp, struct class student[]){
   int num, index;

   //Read in number of records.
   fscanf(ifp, "%d", &num);

   //Read in each record one by one.
   for (index=0; index<num; index++) {
     fscanf(ifp, "%s", student[index].last);
     fscanf(ifp, "%s", student[index].first);
     fscanf(ifp, "%s", student[index].action);

        //If they took a class or are doing grade forgiveness,
        // only scan in hours and grade.

       if(student[index].action == 'TOOK_CLASS' ||
          student[index].action == 'GRADE_FORGIVE'){
               fscanf(ifp, "%d", &student[index].hours);
               fscanf(ifp, "%s", student[index].grade);
                                                   }

        //If they are changing their grade, scan in hours, old grade, and new grade.
       if(student[index].action[] == 'CHANGE_GRADE'){
               fscanf(ifp, "%d", &student[index].hours);
               fscanf(ifp, "%s", student[index].grade);
               fscanf(ifp, "%s", student[index].newgrade);
                                                  }
   }

 return num;

}

Thanks!

In C language you don't test equality of strings using the == operator like you do in c++. you have to use strcmp() for case-sensitive comparisons. I don't think there is a standard C function for case-insensive comparisons, some compilers have stricmp() while others have something like comparenocase().

So an if statement might look like this (assuming action is a char array).

Code:

if( strcmp(student[index].action, "CHANGE_GRADE") == 0)
{
   // do something when true
}

If only string comparisons were that easy in C...

Most string operations will require that you call some kind of string function. The if-else arrangement you have shown would require the use of strcmp(), such as:

Code:

if ( strcmp(student[index].action, "CHANGE_GRADE") == 0 )
{
    // take CHANGE_GRADE action here
}

While this will work, using a string for this type of logic is inefficient both in terms of RAM requirements and performance. A better alternative is to use a simple enumeration and branch on its value, such as:

Code:

typedef enum
{
     CHANGE_GRADE = 0
    ,TOOK_CLASS
    ,GRADE_FORGIVE
} ACTIONS;

...declare the action member of your structure to be of this type and then write your comparisons like this:

Code:

if ( student[index].action == CHANGE_GRADE )
{
    // take CHANGE_GRADE action here
}

Hope this helps...

Edit: Or what Dragon said...slipped in there while I was typing this

Thank you for your help.... the strcmp worked perfect. I knew that I had to use strcmp somewhere, but I was not sure where or how.

I understand the logical error I have, but in the second if statement (for CHANGE_GRADE), technically student[index].grade is really the old grade for the class, (in University terms) so, I did it the way I did for code readability, and compatibility w/ the problem and my comments throughout the code.

Well as long as you have a reason!

I wasn't intending to call what you've done a "logical error", because it's not - it's a valid way to approach the problem. I just tend to restrict my use of strings in C whenever possible because they are awkward to work with...