C Program For Lower Case to Uppercase and Vice-Versa in a File

Given a text file(gfg.txt), our task is to convert all the lowercase characters of the file into uppercase.

Examples

Input: (content inside file gfg.txt)
An extensive classroom programme
by GeeksforGeeks to build and enhance
Data Structures and Algorithm concepts

Output: (content inside file gfg.txt)
AN EXTENSIVE CLASSROOM PROGRAMME
BY GEEKSFORGEEKS TO BUILD AND ENHANCE
DATA STRUCTURES AND ALGORITHM CONCEPTS

Approach

1. Open the file gfg.txt in write mode.
2. Check if there is any error in opening or locating a file.
3. If yes, then throw an error message.
4. If no, write the contents of the reference string into the file and rewind the file pointer.
5. Now, with the help of a while loop, convert all the characters of that file into the upper case using toupper() function and store them in a temporary buffer.
6. Print the temporary buffer into the gfg.txt file.
7. Close the file using fclose() function by passing the file pointer in it.

Program for Lowercase to Uppercase Conversion

C

// C program to convert all lower case characters of a file
// into Upper Case
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

// utility function to print file
void readFile(FILE* fptr)
{
    char ch = fgetc(fptr);
    while (ch != EOF) {
        printf("%c", ch);
        ch = fgetc(fptr);
    }
    printf("\n");
}

int main()
{
    // initializing the file pointer
    FILE* fptr;

    // test string
    char str[500]
        = "An extensive classroom "
          "programme\nby GeeksforGeeks to build and "
          "enhance\nData Structures and Algorithm concepts";

    // name of the file as sample.txt
    char file[50] = { "gfg.txt" };
    char ch;

    // opening the file in read write mode
    fptr = fopen(file, "w");

    // printing data to the file
    fprintf(fptr, "%s", str);
    rewind(fptr);

    // printing initial file
    printf("INITIAL FILE DATA:\n");
    readFile(fptr);
    rewind(fptr);

    ch = fgetc(fptr);
    int i = 0;
    // converting into upper case
    while (ch != EOF) {

        // converting char to upper case
        str[i++] = toupper(ch);
        ch = fgetc(fptr);
    }
    rewind(fptr);

    // printing upper case
    fprintf(fptr, "%s", str);
    rewind(fptr);

    printf("\nFINAL FILE DATA:\n");
    readFile(fptr);

    // closing the file
    fclose(fptr);

    return 0;
}

Output

INITIAL FILE DATA:
An extensive classroom programme
by GeeksforGeeks to build and enhance
Data Structures and Algorithm concepts

FINAL FILE DATA:
AN EXTENSIVE CLASSROOM PROGRAMME
BY GEEKSFORGEEKS TO BUILD AND ENHANCE
DATA STRUCTURES AND ALGORITHM CONCEPTS

Upper Case to Lower Case

Given a text file(gfg.txt), our task is to convert all the uppercase characters of the file into lowercase.

Examples

Input: (content inside file (gfg.txt)
AN EXTENSIVE CLASSROOM PROGRAMME
BY GEEKSFORGEEKS TO BUILD AND ENHANCE
DATA STRUCTURES AND ALGORITHM CONCEPTS

Output: (content inside file (gfg.txt)
an extensive classroom programme
by geeksforgeeks to build and enhance
data structures and algorithm concepts

Approach

1. Open the file gfg.txt in write mode.
2. Check if there is any error in opening or locating a file.
3. If yes, then throw an error message.
4. If no, write the contents of the reference string into the file and rewind the file pointer.
5. Now, with the help of a while loop, convert all the characters of that file into the lower case using tolower() function and store them in a temporary buffer.
6. Print the temporary buffer into the gfg.txt file.
7. Close the file using fclose() function by passing the file pointer in it.

Program for Uppercase to Lowercase Conversion

C

// C program to convert all upper case characters of a file
// into Lower Case
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

// utility function to print file
void readFile(FILE* fptr)
{
    char ch = fgetc(fptr);
    while (ch != EOF) {
        printf("%c", ch);
        ch = fgetc(fptr);
    }
    printf("\n");
}

int main()
{
    // initializing the file pointer
    FILE* fptr;

    // test string
    char str[500]
        = "AN EXTENSIVE CLASSROOM PROGRAMME\nBY "
          "GEEKSFORGEEKS TO BUILD AND ENHANCE\nDATA "
          "STRUCTURES AND ALGORITHM CONCEPTS";

    // name of the file as sample.txt
    char file[50] = { "gfg.txt" };
    char ch;

    // opening the file in read write mode
    fptr = fopen(file, "w");
    if (fptr == NULL) {
        printf("Error Opening File");
        exit(0);
    }

    // printing data to the file
    fprintf(fptr, "%s", str);
    rewind(fptr);

    // printing initial file
    printf("INITIAL FILE DATA:\n");
    readFile(fptr);
    rewind(fptr);

    ch = fgetc(fptr);
    int i = 0;
    // converting into lower case
    while (ch != EOF) {

        // converting char to upper case
        str[i++] = tolower(ch);
        ch = fgetc(fptr);
    }
    rewind(fptr);

    // printing upper case
    fprintf(fptr, "%s", str);
    rewind(fptr);

    printf("\nFINAL FILE DATA:\n");
    readFile(fptr);

    // closing the file
    fclose(fptr);

    return 0;
}

Output

INITIAL FILE DATA:
AN EXTENSIVE CLASSROOM PROGRAMME
BY GEEKSFORGEEKS TO BUILD AND ENHANCE
DATA STRUCTURES AND ALGORITHM CONCEPTS

FINAL FILE DATA:
an extensive classroom programme
by geeksforgeeks to build and enhance
data structures and algorithm concepts

Notes:

1. Run this program offline by making the file gfg.txt and store some characters in it.

2. Make sure that you have made the file with the same name as that used in code and within the same folder where your program is stored.