Program which reads a line of characters & store it in a data file in the opposite case.

#include<stdio.h>

#include<ctype.h>

void main()

{

char a[50];int i;

printf("Enter the line of text:");

scanf("%[^\n]",a);

printf("%s",a);

FILE *fp=fopen("text.dat","w");

for(i=0;a[i]!='\0';i++)

{

if(islower(a[i]))

a[i]=toupper(a[i]);

else a[i]=tolower(a[i]);

fprintf(fp,"%c",a[i]);

}

fclose(fp);

}