[Solved] low level file input output calculate “sum” and “average” [closed]

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Functions read() and write() and their cousins are used for binary files. Reading a text file would be better using fgets() and analysing the contents of each line, then outputting that line with the extra fields you calculate. Bear in mind that fgets() retains any newline, which has to be removed before appending text to that line.

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

#define LLEN 100

int main(void)
{
    FILE *inf, *outf;
    int val1, val2, val3, sum;
    char buff[LLEN];

    if((inf = fopen("input.txt", "rt")) == NULL) {
        perror("Can't open file input.txt");
        exit(1);
    }
    if((outf = fopen("output.txt", "wt")) == NULL) {
        perror("Can\t open file output.txt");
        exit(1);
    }

    if(fgets(buff, LLEN, inf) == NULL) {            // read the header
        perror("Cannot read header line");
        exit(1);
    }
    buff [ strcspn(buff, "\r\n") ] = '\0';          // truncate any newline
    fprintf(outf, "%s sum     average\n", buff);    // write expanded header line

    while(fgets(buff, LLEN, inf) != NULL) {         // read each line
        buff [ strcspn(buff, "\r\n") ] = '\0';      // truncate any newline
        if(sscanf(buff, "%*s%d%d%d", &val1, &val2, &val3) != 3) {   // ignore ID
            perror("Cannot convert fields");
            exit(1);
        }
        sum = val1 + val2 + val3;
        fprintf(outf, "%s%9d%7d \n", buff, sum, sum/3);
    }

    if (fclose(outf))
        perror("Unable to close output file");
    fclose(inf); 
    return 0;
}

Output file:

ID              UNIX    C Language      Network sum     average
20150001        98      95              97      290     96 
20150002        84      88              90      262     87

Incidentally your average was incorrect on the last line!

4

solved low level file input output calculate “sum” and “average” [closed]