Thread: Need help reading next line from input file

You read only the first line because you read only the first line. Call fscanf within your loop.

How to use a loop function with user input in C? - Stack Overflow
Checking for EOF in 6 places can't be the best way, right?

Also, some indenting might reveal some bugs:

Code:

case ('*'):
    printf("%f * %f = %f \n)", i, j, i * j);
    if ( feof(cmd) )
        break; /* break happens only if ... */
case ('/'):
    printf("%f / %f = %f \n)", i, j, i / j);
    if ( feof(cmd) )
        break;

Cases "fall through" each other unless you break; in this case the break refers to the switch, not the loop. You both forgot to break from your cases and mistakenly thought you could exit the loop from within the switch. You'll need something else for that. And why copy the op in your printf format strings when you already have op?

Code:

#include <stdio.h>
#include <stdlib.h>
/* Removed unused macro */
 
int main(void)
{
    float i, j;
    char op; /* H and Q are not used */

    /* Might as well initialize rather than assign */
    FILE* cmd = fopen("CommandsProj1.dat", "r");
    
    if (cmd == NULL)
    {
        printf("File could not be opened");
        return EXIT_FAILURE; /* Something other than zero */
    }
    
    /* Better to keep success in same scope as call, so no 'else' here. */

    /* fscanf returns EOF if it tries to read but
     * isn't able to get any data. So you can put your reading in
     * the loop condition, and when you get to the
     * one-after-last-line, this will be false and 
     * your loop will be done. 
     */
    while (EOF != fscanf(cmd, "%c %f %f", &op, &i, &j))
    {
        float result; 

        switch (op)
        {
            case '+': /* No need for parentheses around the case expressions */
                result = i + j;
                break; /* Breaks from the switch */
            case '-':
                result = i - j;
                break;
            case '*':
                result = i * j;
                break;
            case '/':
                result = i / j;
                break;
            case 'h': /* why not allow lower case too? */
            case 'H':
                printf("Help Menu Coming soon\n");
                continue; /* Continues the loop */
            case 'q':
            case 'Q':
                printf("Goodbye");
                goto cleanupArea; 
                /* goto could be avoided using functions
                   or a "quitting" flag, if you wish */
            default:
                continue; /* So we skip the printf */
        }

        /* reused 'op' here, and removed the ')' */
        printf("%f %c %f = %f \n", i, op, j, result); 
    }

cleanupArea:
    fclose(cmd); 
    return EXIT_SUCCESS; /* The official zero */
}

Originally Posted by CodeMonkey

Code:

while (EOF != fscanf(cmd, "%c %f %f", &op, &i, &j))

This isn't a particularly good idea. EOF isn't the only way that fscanf() reports a problem reading. In the example here, if the file contains bad data, the result will be confusing output (at best).

Mixing continue, break, and goto statements in a switch is really poor form too, unless your goal is to write unnecessarily cryptic code. Note how you have needed to use comments to clarify your intent.


And (for the OP) naming float variables i and j is awful, since i and j are often used to name integers used for counters. Better to use descriptive names. The compiler doesn't care. People trying to understand your code - including yourself in future - will benefit from descriptive variable names.

I think it's the initial "DA" in the file that's not read in before the loop.

Also, ideally, the statement "return EXIT_FAILURE" shouldn't be a return statement. The file is not closed properly. Use an "exit" statement instead:

exit( EXIT_FAILURE);

Originally Posted by xrayextra

Also, ideally, the statement "return EXIT_FAILURE" shouldn't be a return statement. The file is not closed properly. Use an "exit" statement instead:

exit( EXIT_FAILURE);

The return is from the main function so that will make no difference.

Originally Posted by powerfox0

so should I put another case for variable DA? I heard something about flushing input values but am not sure how that works

Why is the "DA" in the input in the first place? If it is not required, then it either shouldn't be there (e.g., you should report an input error to the user) or you should read and discard it (e.g., after determining that it isn't valid input).

Help....

Code:

// PA
#include <stdio.h>
#include <stdlib.h>


int main(void)
{
    float num1, num2;
    char op;


    FILE* cmd = fopen("CommandsProj1.dat", "r");


    if (cmd == NULL)
    {
        printf("File could not be opened");
        return EXIT_FAILURE;
    }


    printf("Welcome to Calculator (Version 1.0)\n");




    while (EOF != fscanf(cmd, "%c %f %f", &op, &num1, &num2))/*  If not End of File, Read data   */
    {
        float result;


        switch (op)
        {
            case '+':
                result = num1 + num2;
                break;
            case '-':
                result = num1 - num2;
                break;
            case '*':
                result = num1 * num2;
                break;
            case '/':
                result = num1 / num2;
                break;
            case 'H':
                printf("\nHelp menu: accepted operations are '+' '-' '*' '/' 'H' 'Q'\n");
                continue;
            case 'Q':
                printf("\nThank you for using Calculator  (Version 1.0)... Goodbye\n");
                goto cleanupArea;
            case 'DA':
                continue;
            default:
                continue;
        }
        printf("\n%4.2f %c %4.2f = %4.2f \n", num1, op, num2, result); /*  Print calculation information.  */
        fflush(stdout);
    }


cleanupArea:


    fclose(cmd); /*  Close file */
    return EXIT_SUCCESS; /*  exit program */
}

still can't figure out why case + or - are not printing to screen

The DA was there originally from my teacher..I even changed input file and removed DA. still not giving me anything printed to screen for + or - as op values....