diff --git a/icu4c/source/test/cintltst/cbiditst.c b/icu4c/source/test/cintltst/cbiditst.c
index ce4c1ce57f28..37d69df48fdb 100644
--- a/icu4c/source/test/cintltst/cbiditst.c
+++ b/icu4c/source/test/cintltst/cbiditst.c
@@ -4539,8 +4539,7 @@ overrideBidiClass(const void *context, UChar32 c) {
           DEF,   DEF,   DEF,   LRO,     B,   RLO,    BN,   DEF  /* 78-7F */
     };
     static const int nEntries = UPRV_LENGTHOF(customClasses);
-    const char *dummy = context;        /* just to avoid a compiler warning */
-    dummy++;
+    (void)context;        /* just to avoid a compiler warning */
 
     return c >= nEntries ? U_BIDI_CLASS_DEFAULT : customClasses[c];
 }
diff --git a/icu4c/source/test/intltest/rbbimonkeytest.cpp b/icu4c/source/test/intltest/rbbimonkeytest.cpp
index cd8436ac30f8..45fe3e43a419 100644
--- a/icu4c/source/test/intltest/rbbimonkeytest.cpp
+++ b/icu4c/source/test/intltest/rbbimonkeytest.cpp
@@ -286,7 +286,7 @@ void BreakRules::compileRules(UCHARBUF *rules, UErrorCode &status) {
     }
 
     UnicodeString emptyString;
-    for (int32_t lineNumber=0; ;lineNumber++) {    // Loop once per input line.
+    for (;;) {    // Loop once per input line.
         if (U_FAILURE(status)) {
             return;
         }
diff --git a/icu4c/source/test/intltest/rbbitst.cpp b/icu4c/source/test/intltest/rbbitst.cpp
index 2afe4b3912df..e95419afc470 100644
--- a/icu4c/source/test/intltest/rbbitst.cpp
+++ b/icu4c/source/test/intltest/rbbitst.cpp
@@ -4178,6 +4178,7 @@ void RBBITest::RunMonkey(BreakIterator *bi, RBBIMonkeyKind &mk, const char *name
             expectedBreaks[breakPos] = 1;
             expectedCount++;
             U_ASSERT(expectedCount<testText.length());
+	    (void)expectedCount;  // Used by U_ASSERT().
         }
 
         // Find the break positions using forward iteration
diff --git a/icu4c/source/test/intltest/utxttest.cpp b/icu4c/source/test/intltest/utxttest.cpp
index 21ea2c29839b..fb8c9c32dd96 100644
--- a/icu4c/source/test/intltest/utxttest.cpp
+++ b/icu4c/source/test/intltest/utxttest.cpp
@@ -446,11 +446,10 @@ void UTextTest::TestCopyMove(const UnicodeString &us, UText *ut, UBool move,
         // Compare the results of the two parallel tests
         int32_t  usi = 0;    // UnicodeString position, utf-16 index.
         int64_t  uti = 0;    // UText position, native index.
-        int32_t  cpi;        // char32 position (code point index)
         UChar32  usc;        // code point from Unicode String
         UChar32  utc;        // code point from UText
         utext_setNativeIndex(targetUT, 0);
-        for (cpi=0; ; cpi++) {
+        for (;;) {
             usc = targetUS.char32At(usi);
             utc = utext_next32(targetUT);
             if (utc < 0) {
@@ -522,12 +521,11 @@ void UTextTest::TestReplace(
     //
     int32_t  usi = 0;    // UnicodeString position, utf-16 index.
     int64_t  uti = 0;    // UText position, native index.
-    int32_t  cpi;        // char32 position (code point index)
     UChar32  usc;        // code point from Unicode String
     UChar32  utc;        // code point from UText
     int64_t  expectedNativeLength = 0;
     utext_setNativeIndex(targetUT, 0);
-    for (cpi=0; ; cpi++) {
+    for (;;) {
         usc = targetUS.char32At(usi);
         utc = utext_next32(targetUT);
         if (utc < 0) {
diff --git a/icu4c/source/tools/genrb/rle.c b/icu4c/source/tools/genrb/rle.c
index f737c4549141..0025be207e94 100644
--- a/icu4c/source/tools/genrb/rle.c
+++ b/icu4c/source/tools/genrb/rle.c
@@ -92,13 +92,12 @@ encodeRunByte(uint16_t* buffer,uint16_t* bufLimit, uint8_t value, int32_t length
     return buffer;
 }
 
-#define APPEND( buffer, bufLimit, value, num, status) UPRV_BLOCK_MACRO_BEGIN { \
+#define APPEND( buffer, bufLimit, value, status) UPRV_BLOCK_MACRO_BEGIN { \
     if(buffer<bufLimit){                    \
         *buffer++=(value);                  \
     }else{                                  \
         *status = U_BUFFER_OVERFLOW_ERROR;  \
     }                                       \
-    num++;                                  \
 } UPRV_BLOCK_MACRO_END
 
 /**
@@ -107,29 +106,28 @@ encodeRunByte(uint16_t* buffer,uint16_t* bufLimit, uint8_t value, int32_t length
  */
 static uint16_t*
 encodeRunShort(uint16_t* buffer,uint16_t* bufLimit, uint16_t value, int32_t length,UErrorCode* status) {
-    int32_t num=0;
     if (length < 4) {
         int j=0;
         for (; j<length; ++j) {
             if (value == (int32_t) ESCAPE){
-                APPEND(buffer,bufLimit,ESCAPE, num, status);
+                APPEND(buffer,bufLimit,ESCAPE, status);
 
             }
-            APPEND(buffer,bufLimit,value,num, status);
+            APPEND(buffer,bufLimit,value,status);
         }
     }
     else {
         if (length == (int32_t) ESCAPE) {
             if (value == (int32_t) ESCAPE){
-                APPEND(buffer,bufLimit,ESCAPE,num,status);
+                APPEND(buffer,bufLimit,ESCAPE,status);
 
             }
-            APPEND(buffer,bufLimit,value,num,status);
+            APPEND(buffer,bufLimit,value,status);
             --length;
         }
-        APPEND(buffer,bufLimit,ESCAPE,num,status);
-        APPEND(buffer,bufLimit,(uint16_t) length, num,status);
-        APPEND(buffer,bufLimit,(uint16_t)value, num, status); /* Don't need to escape this value */
+        APPEND(buffer,bufLimit,ESCAPE,status);
+        APPEND(buffer,bufLimit,(uint16_t) length,status);
+        APPEND(buffer,bufLimit,(uint16_t)value, status); /* Don't need to escape this value */
     }
     return buffer;
 }
diff --git a/icu4c/source/tools/genrb/wrtjava.cpp b/icu4c/source/tools/genrb/wrtjava.cpp
index cb04b5a44ab9..65a1920ad775 100644
--- a/icu4c/source/tools/genrb/wrtjava.cpp
+++ b/icu4c/source/tools/genrb/wrtjava.cpp
@@ -330,7 +330,6 @@ string_write_java(const StringResource *res,UErrorCode *status) {
 static void
 array_write_java(const ArrayResource *res, UErrorCode *status) {
 
-    uint32_t  i         = 0;
     const char* arr ="new String[] { \n";
     struct SResource *current = nullptr;
     UBool allStrings    = true;
@@ -342,7 +341,6 @@ array_write_java(const ArrayResource *res, UErrorCode *status) {
     if (res->fCount > 0) {
 
         current = res->fFirst;
-        i = 0;
         while(current != nullptr){
             if(!current->isString()){
                 allStrings = false;
@@ -370,7 +368,6 @@ array_write_java(const ArrayResource *res, UErrorCode *status) {
             if(U_FAILURE(*status)){
                 return;
             }
-            i++;
             current = current->fNext;
         }
         T_FileStream_write(out,"\n",1);