How to take data from one file and put it into another in C [closed]

Question

Here is the code

#include <stdio.h>

int main(void)
{
    int a, b,sum;
    FILE *in; 
    FILE *out; 

    in=fopen("numbers.txt","r");
    out=fopen("sums.txt","w");

    if(in== || out==NUll){

        printf("File open failed.\n");
        return 0;
    }
    else{
        fscanf(in,"%d %d",&a,&b);
        sum=a+b;
        fprintf(out,"%d %d %d",a,b,sum);
        fclose(in);
        fclose(out);
    }

    return 0;
}

numbers.txt is in the form

a b
a b
etc..

so i am trying to take a and b and then inside sums.txt print out a, b and then the sum of the two. thanks.

Answer 1

Suggested changes:

#include <stdio.h>

int main(void)
{
    int a, b,sum;
    FILE *in; 
    FILE *out; 

    in=fopen("numbers.txt","r");
    out=fopen("sums.txt","w");
    if((!in) || !(out)){
        perror("File open failed.\n");
        return 1;
    }
    else{
        int n = fscanf(in,"%d %d",&a,&b);
        if (n != 2) {
          printf("File read error!\n");
        } else {
          sum=a+b;
          fprintf(out,"%d %d %d",a,b,sum);
        }
        fclose(in);
        fclose(out);
    }
    return 0;
}

• perror() can help give you a more meaningful error message
• As others have pointed out, if(in== || out==NUll) is incorrect.
• It's important to check the return value from fscanf() to ensure you've read the expected data correctly.

'Hope that helps!

Answer 2

Put the code that reads and writes in a loop.

    else{
        while(fscanf(in,"%d %d",&a,&b) == 2) {
            sum=a+b;
            fprintf(out,"%d %d %d\n",a,b,sum);
        }
        fclose(in);
        fclose(out);
    }