Fix warning 'array subscript of type char'

fold.c

@@ -75,21 +75,23 @@ foldline(const char *str, long width)
 	bool space;
 	long col, j;
 	size_t i = 0, n = 0;
+	int c;
 
 	do {
 		space = false;
 		for(j = i, col = 0; str[j] && col <= width; j++) {
-			if(!UTF8_POINT(str[j]) && !bflag)
+			c = str[j];
+			if(!UTF8_POINT(c) && !bflag)
 				continue;
-			if(sflag && isspace(str[j])) {
+			if(sflag && isspace(c)) {
 				space = true;
 				n = j+1;
 			}
 			else if(!space)
 				n = j;
 
-			if(!bflag && iscntrl(str[j]))
-				switch(str[j]) {
+			if(!bflag && iscntrl(c))
+				switch(c) {
 				case '\b':
 					col--;
 					break;

sort.c

@@ -172,7 +172,7 @@ linecmp(const char **a, const char **b)
 static int
 parse_flags(char **s, int *flags, int bflag)
 {
-	while(isalpha(**s))
+	while(isalpha((int)**s))
 		switch(*((*s)++)) {
 		case 'b':
 			*flags |= bflag;

split.c

@@ -41,7 +41,7 @@ main(int argc, char *argv[])
 		size = strtoull(tmp, &end, 10);
 		if(*end == '\0')
 			break;
-		switch(toupper(*end)) {
+		switch(toupper((int)*end)) {
 		case 'K':
 			scale = 1024;
 			break;