just trying to read a goddamned file

jcl/TXTWKR01.jcl

@@ -1,6 +1,5 @@
-//TXTWKR01 JOB (JCC),'JCC File I/O Test',
-//         NOTIFY=@05054,CLASS=A,MSGCLASS=H,
+//TXTWKR01 JOB (GCC),'File I/O Test',NOTIFY=@05054,CLASS=A,MSGCLASS=H,
 //         MSGLEVEL=(1,1),REGION=4M,TIME=1440
-//STEP1   EXEC JCCCLG,INFILE='@05054.SRCLIB.C(TXTWKR01)'
+//STEP1   EXEC GCCCG,INFILE='@05054.SRCLIB.C(TXTWKR01)'
 //GO.TESTDD DD DSN=@05054.DATA(TESTMEM),DISP=SHR,
 //             DCB=(RECFM=FB,LRECL=80,BLKSIZE=0,DSORG=PS)

src/TXTWKR01.c

@@ -1,26 +1,46 @@
-#include <stdio>
+#include <stdio.h>
+#include <string.h>
 
-int main()
+#define MAX_LINES 100
+#define LINE_LEN  256
+
+int main(void)
 {
-    printf((char *)"Program starting - about to fopen(dd:TESTDD, \"r\")\n");
-
     FILE *fp;
-    char buf[256];
+    char lines[MAX_LINES][LINE_LEN];
+    int count = 0;
+    char buf[LINE_LEN];
 
+    /* === Read phase === */
     fp = fopen("dd:TESTDD", "r");
     if (fp == NULL) {
-        printf((char *)"fopen returned NULL\n");
-        printf((char *)"fopen read failed\n");
+        fputs("Cannot open for read\n", stdout);
         return 1;
     }
 
-    printf((char *)"fopen succeeded!\n");
-    printf((char *)"Existing content:\n");
-    while (fgets(buf, 256, fp) != NULL) {
-        printf((char *)"%s", buf);
+    fputs("Existing content:\n", stdout);
+    while (fgets(buf, LINE_LEN, fp) && count < MAX_LINES) {
+        fputs(buf, stdout);                   /* echo to JES */
+        strncpy(lines[count], buf, LINE_LEN-1);
+        lines[count][LINE_LEN-1] = '\0';
+        count++;
     }
     fclose(fp);
 
-    printf((char *)"Read complete.\n");
+    /* === Write phase (rewrite everything + append) === */
+    fp = fopen("dd:TESTDD", "w");
+    if (fp == NULL) {
+        fputs("Cannot open for write\n", stdout);
+        return 1;
+    }
+
+    for (int i = 0; i < count; i++) {
+        fputs(lines[i], fp);
+    }
+    fputs("Appended from C program!\n", fp);
+
+    fclose(fp);
+
+    fputs("Append complete (via rewrite).\n", stdout);
     return 0;
 }