This is a plain C language. The following is a snippet of my codes:

 cal(data1, data2, rows); rmse12, rmse13, rmse14, rmse23, rmse24, rmse34; cal12= cal(data1, data2, rows); cal13= cal(data1, data3, rows); cal14= cal(data1, data4, rows); cal23= cal(data2, data3, rows); cal24= cal(data2, data4, rows); cal34= cal(data3, data4, rows);

Then, I get errors like the following:

156:2: warning: implicit declaration of function 'cal' [-Wimplicit-function-declaration] 156 | cal(data1, data2, rows) ^ error: 'cal12' undeclared (first use in this function) 159 | cal12= cal(data1, data2, rows); | ^~~~~ 

Any feedback to fix these errors would be appreciated. Thank you.