如何在 c 编程中找到 atof function 中的数字总和

Question

1. The code has to read the text file
2. extract numbers and find their average
3. I have already extracted numbers and placed them in a ATOF function

My code can read the file and extract numbers but i dont know how to find the sum of the numbers extracted and find the average. I need help in the modification of my code cause am not too familiar with the atof function

Sample input text file

LivingTemp1,17.8
LivingTemp2,17.9
LivingTemp1,18.1
LivingTemp2,18.2
LivingTemp1,18.5
LivingTemp2,18.6
LivingTemp1,19.0
LivingTemp2,19.0
LivingTemp1,19.5
LivingTemp2,19.6
LivingTemp1,20.0
LivingTemp2,20.1
LivingTemp1,20.6
LivingTemp2,20.6
LivingTemp1,19.8
LivingTemp2,19.8
LivingTemp1,19.4
LivingTemp2,19.5
LivingTemp1,19.0
LivingTemp2,19.1
LivingTemp1,18.5
LivingTemp2,18.6
LivingTemp1,18.0
LivingTemp2,18.1

---

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

void main()
{
    FILE *fp = fopen("test.txt", "r"); `opening the text file`
    FILE *fp1 = fopen("test.txt", "r");
    const char s[2] = ", ";
    char *token;
    char c;
    int count = 1;
    int i;
    int number[24];

    if(fp != NULL)
    {
        char line[24];

        while(fgets(line, sizeof line, fp) != NULL)
        {
            token = strtok(line, s); // ignoring the commas

            for(i=0;i<2;i++)
            {
                if(i==0)
                {
                    //printf("%s\t",token);
                    token = strtok(NULL,s);
                } else {    
                    double num = atof(token);
                    printf("%.1f\n",num);   // printing the extracted numbers    
                }
            }
        }

        for (c = getc(fp1); c != EOF; c = getc(fp1)){
            // countingthe number of lines the text file contains
            if (c == '\n') // Increment count if this character is newline
                count = count + 1;
        }

        printf("The file has %d lines\n ",count);    

        fclose(fp);
    } else {
        perror("test.txt");
    }
}

Answer 1

Your task is very simple: Convert the second token of each line into a floating-point number. If the conversion succeeds, add that number to the sum and increase the data count. Finally, report your data, but beware of division by zero.

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

int main(void)              // main returns int, not void
{
    char line[80];          // make the line bige enough
    int count = 0;          // the count starts at zero, not at one
    double sum = 0.0;

    const char *filename = "test.txt";
    FILE *fp = fopen(filename, "r");

    if (fp == NULL) {
        fprintf(stderr, "Could not open '%s'.\n", filename);
        exit(1);
    }

    while (fgets(line, sizeof line, fp)) {
        const char *sep = ",";              // don't include the space
        char *token = strtok(line, sep);

        if (token == NULL) continue;        // skip empty lines

        token = strtok(NULL, sep);

        if (token) {
            double T = atof(token);

            if (T) {
                sum += T;
                count++;
            }
        }
    }

    fclose(fp);

    if (count) {
        printf("Number of measurements: %d\n", count);
        printf("Average temperature:    %g\n", sum / count);
    } else {
        puts("No data!");
    }

    return 0;
}

The function atof is very simple and returns 0.0 if a number cannot be converted. That means you canot distinguish between the actual number 0, which is a likely temperature in centegrade, and conversion failure. The function strtod offers you better disgnostics.

Answer 2

Here is a simpler version:

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

int main()
{
  int living, n, count=0;
  double value, sum = 0.0;

  FILE *fp = fopen("test.txt", "r"); //`opening the text file`
  if( !fp ) err(EXIT_FAILURE, "no input");

  while( (n = fscanf(fp, "LivingTemp%d,%lf ", &living, &value)) == 2 ) {
    count++;
    sum += value;
  }

  if( n != EOF ) {
    errx(EXIT_FAILURE, "failed to parse line %d", count);
  } 

  if( !feof(fp) ) {
    err(EXIT_FAILURE, "failed to read file");
  }

  printf( "average of %d values is %f\n", count, sum / count );

  return EXIT_SUCCESS;
}

Just for grins, I also parse the "living" number. ISTM in a real-world case you'd need to compute averages and counts by identifier. The value is parsed out in case you want it.

Normally I recommend reading a line before scanning it. In your case your input is well specified, and you can scan it directly. Note this also compensates for blank lines because the format string ends in whitespace. It has the disadvantage of aborting on the first failed parse, rather than reporting errors and continuing to end of file.

The scanf (3) functions are IMO generally under-appreciated. One scanf statement saves you reinventing tokenizing, skipping whitespace, and individually converting each component. Note for example that failure to convert shows up in the conversion count (returned by the function).