C change words beginning with lowercase to capital in text file

Question

Well I try to read a file and change every word that's beginning with a lowercase to the same word beginning with an uppercase.

This is what i got:

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

int main()
{
FILE *fp;
int zeichen;

fp = fopen("test.txt", "r+");

if(fp == NULL){
    printf("Die Datei konnte nicht geoeffnet werden.\n");
}
else{
    fseek(fp, 0L, SEEK_SET);
    zeichen = fgetc(fp);
    while(zeichen != EOF){
        if(zeichen == ' '){
            fseek(fp, 1L, SEEK_CUR);
            if(('a' <= zeichen) && (zeichen <= 'z')){
                zeichen = fgetc(fp);
                fputc(toupper(zeichen), fp);
            }
        }
        zeichen = fgetc(fp);
    }
    zeichen = fgetc(fp);
    fclose(fp);
}
return 0;
}

My test.txt file does not change at all.

Any suggestions what i am doing wrong?

EDIT:

Thank you for the different ways to achieve my task.

Most of them where using stuff i didn't learn yet, so i tried it by copying the characters from one file to another + making the first letter of each word an uppercase by toupper() cause it's indeed easy to use. Then deleting the old file + rename the new one.

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

int main()
{
    FILE *fp, *neu;
    int zeichen;

    fp = fopen("test.txt", "r");
    neu = fopen("new.txt", "w");

    if(fp == NULL) {
        printf("Die Datei konnte nicht geoeffnet werden.\n");
        exit(EXIT_FAILURE);
    }

    while((zeichen = fgetc(fp)) != EOF) {
        if(zeichen == ' ') {
            fputc(zeichen, neu);
            zeichen = fgetc(fp);
            zeichen = toupper(zeichen);
            fputc(zeichen, neu);
        }
        else{
            fputc(zeichen, neu);
        }
    }
    fclose(fp);
    fclose(neu);
    remove("test.txt");
    rename("new.txt", "test.txt");
    printf("File has been changed.\n");
    return 0;
}

Answer 1

FILE *fp;
int zeichen;

fp = fopen("test.txt", "r+");

if (fp == NULL) {
    printf("Die Datei konnte nicht geoeffnet werden.\n");
    exit(EXIT_FAILURE);
}

// upper first charcter
zeichen = getc(fp);
if (zeichen != EOF) putchar(toupper(zeichen));

// scan rest of chars
while ((zeichen = getc(fp)) != EOF) {
    putchar(zeichen);
    if (zeichen == ' ' && zeichen != EOF) {
        char c_upper = getc(fp);
        putchar(toupper(c_upper));
    }
}
fclose(fp);
return 0;

you can use std out redirection ./main > output.txt