Added modulo program

Makefile

@@ -1,4 +1,4 @@
-files = add div mean mul sub sum
+files = add div mean mod mul sub sum
 
 all: $(files)
 

mod.c

@@ -0,0 +1,25 @@
+#include <stdio.h>
+#ifndef eprintf
+#define eprintf(...) fprintf(stderr, __VA_ARGS__)
+#endif
+
+int main(int argc, char **argv) {
+  int v1;
+  int v2;
+  int out;
+  int e1;
+  int e2;
+
+  e1 = sscanf(argv[1], "%i", &v1);
+  e2 = sscanf(argv[2], "%i", &v2);
+  if(e1==EOF) {
+    eprintf("%s: argument 1 cannot be parsed as int", *argv);
+    return 1;
+  } else if(e2==EOF) {
+        eprintf("%s: argument 2 cannot be parsed as int", *argv);
+    return 1;
+  }
+  out=v1%v2;
+  printf("%d\n",out);
+  return 0;
+}