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[jurka]

Writing to file is really simple in C there's only three functions(fopen, fprintf, fclose) which you should know and one structure(FILE). This code snippet creates a file with 0 - 100 lines of numbers.

Code

GeSHi (c):
#include <stdio.h>
 
int main(int argc, char **argv) {
        FILE *fp;
        char *filename = "database";
 
        // Open file for writing
        fp = fopen(filename, "w");
 
        // Check for problems with opening file
        if (fp == NULL) {
                printf("Problem with opening file %s\n", filename);
                return 1;
        }
 
        int i;
        for (i = 0; i <= 100; i++) {
                // Write to file similar to function printf
                fprintf(fp, "%d\n", i);
        }
 
        fclose(fp);
 
        return 0;
 
}
 
 
Created by GeSHI 1.0.7.20

And the reading is also easy new function is scanf() and constant EOF.

Code

GeSHi (c):
#include <stdio.h>
 
int main(int argc, char **argv) {
        FILE *fp;
        char *filename = "database";
 
        // Open file for reading
        fp = fopen(filename, "r");
 
        // Check for problems with opening file
        if (fp == NULL) {
                printf("Problem with opening file %s\n", filename);
                return 1;
        }
        int temp;
 
        // EOF stands for end of file, so it checks if
        // it's not already in the end
        while(fscanf(fp, "%d", &temp) != EOF) {
                // Make some arithmetics
                temp += 10;
                printf("%d\n", temp);
        }
 
        // Close file
        fclose(fp);
 
        return 0;
 
}
 
 
Created by GeSHI 1.0.7.20

[trey]

Eh, well you covered some of the formatted IO functions (fscanf and fprintf), but there are plenty of other IO functions:

fread(void*, size_t, size_t, FILE*)
fgetc(FILE*) (or getc(FILE*) if you wish to use it as a macro)
fgets(char*, int, FILE*)

Those are only a couple off the top of my head, but there are a few others for general stdin IO. You may also want to explain formatted IO a bit, as far as what the different conversion specifiers mean (%i, %s, %d, %x, etc.)