/* Upper and lower case letter functions */
#include <stdio.h>
#include <ctype.h> /* Note - your compiler may not need this */
void mix_up_the_chars(char line[]);
void main()
{
FILE *fp;
char line[80], filename[24];
char *c;
printf("Enter filename -> ");
scanf("%s",filename);
fp = fopen(filename,"r");
do {
c = fgets(line,80,fp); /* get a line of text */
if (c != NULL) {
mix_up_the_chars(line);
}
} while (c != NULL);
fclose(fp);
}
void mix_up_the_chars(char line[])
/* This function turns all upper case
characters into lower case, and all
lower case to upper case. It ignores
all other characters. */
{
int index;
for (index = 0;line[index] != 0;index++) {
if (isupper(line[index])) /* 1 if upper case */
line[index] = tolower(line[index]);
else {
if (islower(line[index])) /* 1 if lower case */
line[index] = toupper(line[index]);
}
}
printf("%s",line);
} UPLOW.C
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