Reduce some var scopes

armsrc/string.c

@@ -80,10 +80,10 @@ char *strcat(char *dest, const char *src) {
 
 /* reverse:  reverse string s in place */
 void strreverse(char s[]) {
-    int c, i, j;
+    int j = strlen(s) - 1;
 
-    for (i = 0, j = strlen(s) - 1; i < j; i++, j--) {
-        c = s[i];
+    for (int i = 0; i < j; i++, j--) {
+        int c = s[i];
         s[i] = s[j];
         s[j] = c;
     }