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C - Convert All Characters in Upper Case of a File using C Program

In this program (code snippet) we will learn how to convert all characters of a file in uppercase using c program file handling?

In this example there is a file "sample.txt" which contains "This is sample.txt file document." we will read all characters and convert them into uppercase and write into the temporary file then rename temporary file to sample.txt and remove temp.txt file.

C Code: Convert All Characters in Upper Case of a File using C Program

/*C - Convert All Characters in Uppercase 
of a File using C Program.*/
 
 
#include <stdio.h>
#include <ctype.h>
 
int main(){
 
    //file nane
    const char *fileName="sample.txt";
    //file pointers
    FILE *fp,*fp1;
    //to store read character
    char ch;
     
    //open file in read mode
    fp=fopen(fileName,"r");
    if(fp==NULL){
        printf("Error in opening file.\n");
        return -1;
    }
    //create temp file
    fp1=fopen("temp.txt","w");
    if(fp1==NULL){
        printf("Error in creating temp file.\n");
        return -1;
    }   
    //read file from one file and copy
    //into another in uppercase
    while((ch=fgetc(fp))!=EOF){
        if(islower(ch)){
            ch=ch-32;
        }
        //write character into temp file
        putc(ch,fp1);                   
    }
    fclose(fp);
    fclose(fp1);
    //rename temp file to sample.txt
    rename("temp.txt","sample.txt");
    //remove temp file
    remove("temp.txt");
     
    //now, print content of the file
    //open file in read mode
    fp=fopen(fileName,"r");
    if(fp==NULL){
        printf("Error in opening file.\n");
        return -1;
    }
    printf("Content of file\n");
    while((ch=getc(fp))!=EOF){
        printf("%c",ch);
    }
    printf("\n");
    fclose(fp);
    return 0;
}

Output

    Content of file 
    THIS IS SAMPLE.TXT FILE DOCUMENT.

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