diff --git a/.gitignore b/.gitignore
index e46264a..170c003 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 tests.out
+test_prg
\ No newline at end of file
diff --git a/src/Makefile b/src/Makefile
new file mode 100644
index 0000000..83cf61b
--- /dev/null
+++ b/src/Makefile
@@ -0,0 +1,12 @@
+output: main.o isogram.o
+	gcc main.o isogram.o -o isogram
+
+main.o: main.c
+	gcc -c main.c -o main.o
+
+isogram.o: isogram.c isogram.h
+	gcc -c isogram.c
+
+clean:
+	rm -rf main.o isogram.o isogram
+
diff --git a/src/isogram.c b/src/isogram.c
index c4078c4..b5dca2b 100644
--- a/src/isogram.c
+++ b/src/isogram.c
@@ -6,9 +6,23 @@
 
 
 bool is_isogram(const char phrase[]){
-    // this is the documentation
-    if (false) {
-        printf("hello world\n");
+    int i = 0;
+    int freq[256] = {0};
+    while (phrase[i] != '\0'){
+        char c = phrase[i];
+        freq[c]++;
+        i++;
+    }
+    int max = 0;
+    for (int i = 0; i < 256 ; i++){
+        if (freq[i] != 0) {
+        // first time?
+            if (max == 0){
+                max = freq[i]; // keep track of the real frequenz
+            } else if (freq[i] != max){
+                return false;
+            }
+        }
     }
     return true;
 }
diff --git a/src/isogram.h.gch b/src/isogram.h.gch
new file mode 100644
index 0000000..83bd06f
Binary files /dev/null and b/src/isogram.h.gch differ
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..d66d5af
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,11 @@
+#include "isogram.h"
+#include <stdio.h>
+
+int main(int arg, char *argv[]){
+    if (is_isogram(argv[1])){
+        printf("The Pharse is an isogram.\n");
+    }else {
+        printf("The pharse is not an isogram.\n");
+    }
+    return 0;
+}
\ No newline at end of file
diff --git a/src/test.c b/src/test.c
new file mode 100644
index 0000000..5decb62
--- /dev/null
+++ b/src/test.c
@@ -0,0 +1,31 @@
+#define UNITY_OUTPUT_COLOR
+ 
+#include "isogram.h"
+#include <string.h>
+#include <stdio.h>
+ 
+ 
+bool is_isogram(const char phrase[]){
+ 
+    int i = 0;
+    int freq[256] = {0};
+ 
+    while(phrase[i] != '\0'){
+        char c = phrase[i];
+        freq[c]++;
+        i++;
+    }
+    int max = 0;
+    for (int i = 0; i<256; i++) {
+        if (freq[i] != 0) {
+            //first time
+            if(max == 0) {
+                max = freq[i];
+            } else if(freq[i] != max) {
+                return false;
+            }
+    }
+}
+ 
+    return true;
+}
\ No newline at end of file
diff --git a/test_prg b/test_prg
new file mode 100755
index 0000000..6c289ea
Binary files /dev/null and b/test_prg differ