Added implementation in C of the first exercise.

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..fdae438
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,14 @@
+PROGRAMS=\
+	l30_1_missing_number
+
+all:$(PROGRAMS)
+
+LINE=----------------------------------------
+run-all:all
+	@echo "$(LINE)"
+	@for p in $(PROGRAMS) ; do echo "$$p" ; ./$$p ; echo "$(LINE)" ; done
+
+clean:
+	-rm -rf $(PROGRAMS) *.o *.dSYM
+
+.PHONY: run-all
diff --git a/l30_1_missing_number.c b/l30_1_missing_number.c
new file mode 100644
index 0000000..f068a66
--- /dev/null
+++ b/l30_1_missing_number.c
@@ -0,0 +1,71 @@
+/*
+Read more: http://javarevisited.blogspot.com/2015/06/top-20-array-interview-questions-and-answers.html
+*/
+
+
+/*
+1. How to find missing number in integer vector of 1 to 100?
+
+You have given an integer vector which contains numbers from 1 to 100
+but one number is missing, you need to write a Lisp program to find
+that missing number in vector.
+
+One trick to solve this problem is calculate sum of all numbers in
+vector and compare with expected sum, the difference would be the
+missing number.
+*/
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <time.h>
+
+int sum_vector(int vector[],int size){
+    int s=0;
+    for(int i=0;i<size;++i){
+        s+=vector[i];
+    }
+    return s;
+}
+
+
+int sum_1_to_n(int n){
+    return n*(n+1)/2;
+}
+
+
+int fill_vector(int vector[],const int N,const int missing){
+    int size=0;
+    for(int i=1;i<=N;++i){
+        if(i!=missing){
+            vector[size++]=i;
+        }
+    }
+    return size;
+}
+
+
+void l30_1(){
+    const int N=100;
+    int vector[N];
+    int actual_missing=1+rand()%N;
+    int size=fill_vector(vector,N,actual_missing);
+    int expected_sum=sum_1_to_n(N);
+    int actual_sum=sum_vector(vector,size);
+    int computed_missing=expected_sum-actual_sum;
+    printf("  actual missing = %3d\n",actual_missing);
+    printf("computed missing = %3d\n",computed_missing);
+    if(computed_missing==actual_missing){
+        printf("yay!\n");
+    }else{
+        printf("bummer!\n");
+    }
+}
+
+
+int main(){
+    srand(clock());
+    l30_1();
+    return 0;
+}
+
+/* THE END */