C read file lines and print them

Question

I want to read a .dat file whose first line consists of a float and all consecutive lines are "int * int" or "int / int" and print or return whether the float is a result each division or multiplication. I am very unpleased with the results that I am getting. My experience is limited to only a couple of hours doing C. Therefore I have no idea what is missing for the program to do what the code is looking like it would do.

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

int countlines(FILE* f){
    int nLines = -1;
    char xLine[10];
    while(fgets(xLine,10,f)!=NULL){
        nLines+=1;
    }
    return nLines;
}

int main(){

    FILE * fPointer = fopen("test.dat", "r");

    float dpFloat;
    char oprnd[10];
    int frstInt;
    int scndInt;

    //get float from first line
    fscanf(fPointer, "%f", &dpFloat);

    //count amount of lines below float
    int amtLines = countlines(fPointer);

    //loop through the other lines and get 
    int i;
    for (i = 0; i < amtLines; i++){

        fscanf(fPointer, "%d %s %d", &frstInt, oprnd, &scndInt);

        //checking what has been read
        printf("%d. %d %s %d\n", i, frstInt, oprnd, scndInt);

        //print 1 if firstline float is quot/prod of consecutive line/s
        //else 0
        if (strcmp(oprnd,"*") ==1) printf("%i\n", (frstInt*scndInt)==dpFloat);
        if (strcmp(oprnd,"/") ==1) printf("%i\n", (frstInt/scndInt)==dpFloat);

    }

    fclose(fPointer);
    return 0;
}

Thanks alot! I fixed it by counting the lines first in the main function and then using rewind(fPointer) before proceeding with getting the float from first line. — Jay Doe, Oct 26 '15 at 21:42

score 2 · Answer 1 · edited May 23 '17 at 11:59

2

Problem 1: strcmp returns 0 when its arguments are equal, not 1.
Problem 2: frstInt/scndInt will truncate the result. Fix it by adding 1.0* to the expression.

The lines

    if (strcmp(oprnd,"*") ==1) printf("%i\n", (frstInt*scndInt)==dpFloat);
    if (strcmp(oprnd,"/") ==1) printf("%i\n", (frstInt/scndInt)==dpFloat);

need to be

    if (strcmp(oprnd,"*") == 0) printf("%i\n", (frstInt*scndInt)==dpFloat);
    if (strcmp(oprnd,"/") == 0) printf("%i\n", (1.0*frstInt/scndInt)==dpFloat);
                       //   ^^^                 ^^^

Please be aware of the pitfalls of comparing floating point numbers. It's best to compare them within a tolerance. See Comparing floating point numbers in C for some helpful tips.

edited May 23 '17 at 11:59

Community

1
1

answered Oct 26 '15 at 21:10

R Sahu

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Thanks, apparently I overlooked how strcmp exactly works. – Jay Doe Oct 26 '15 at 21:42
Note: It is unclear from OP's post if `1.0*` is needed. A similar argument could be made for `(1.0*frstInt*scndInt)` to cope with overflow. Sample OP data and expectations would help – chux - Reinstate Monica Oct 26 '15 at 21:43
Regarding Problem 2: Thanks for the Hint. So far our first line number is an int converted to float, e.g. 506.0, so I wouldnt even have noticed! I'll add sample data and expectations more clearly next time :) – Jay Doe Oct 26 '15 at 21:48

C read file lines and print them

1 Answers1