diff --git a/ssd1306.c b/ssd1306.c
--- a/ssd1306.c
+++ b/ssd1306.c
@@ -250,7 +250,7 @@ void ssd1306_drawlogo()
 
     setStartPage(0);
     setStartColumn(0);
-    for(i = 0; i<32; i++)
+    for(i = 0; i < 32; i++)
     {
         WriteData(row[3][i]);
     }
@@ -260,15 +260,14 @@ void ssd1306_drawlogo()
 /* Print a single character from font.cpp */
 void ssd1306_drawchar(char ascii, unsigned char row, unsigned char xPos)
 {
-    char *srcPointer = -1;
-    unsigned char i;
+    const char *srcPointer = (char*)-1;
 
     srcPointer = &fontData[(ascii-32)][0];
 
     setStartPage(row);
     setStartColumn(xPos);
 
-    for(i=0;i<5;i++)
+    for(uint8_t i = 0; i < 5; i++)
     {
         WriteData(*srcPointer);
         srcPointer++;
@@ -278,8 +277,7 @@ void ssd1306_drawchar(char ascii, unsign
 
 void ssd1306_drawcharbig(char ascii, unsigned char row, unsigned char xPos)
 {
-    char *srcPointer = -1;
-    unsigned char i;
+    const char *srcPointer = (char*)-1;
 
     srcPointer = &fontData[(ascii-32)][0];
 
@@ -287,7 +285,7 @@ void ssd1306_drawcharbig(char ascii, uns
     setStartColumn(xPos);
 
     // Write first row
-    for(i=0;i<5;i++)
+    for(uint8_t i = 0; i < 5; i++)
     {
         uint8_t data = 0;
         data |= ((*srcPointer) & 0b1000) << 4; // get top 4 bits
@@ -315,7 +313,7 @@ void ssd1306_drawcharbig(char ascii, uns
     setStartColumn(xPos);
 
     // Write second row
-    for(i=0;i<5;i++)
+    for(uint8_t i = 0; i < 5; i++)
     {
         uint8_t data = 0;
         data |=  (*srcPointer) & 0b10000000; // get top 4 bits