Compilare: main.c: In function 'backtrack': main.c:18:9: warning: implicit declaration of function 'calc' [-Wimplicit-function-declaration] calc(); ^~~~ main.c: At top level: main.c:28:6: warning: conflicting types for 'calc' void calc(){ ^~~~ main.c:18:9: note: previous implicit declaration of 'calc' was here calc(); ^~~~ main.c: In function 'read': main.c:10:5: warning: ignoring return value of 'fscanf', declared with attribute warn_unused_result [-Wunused-result] fscanf(fin,"%d%d",&n,&m); ^~~~~~~~~~~~~~~~~~~~~~~~ main.c:13:13: warning: ignoring return value of 'fscanf', declared with attribute warn_unused_result [-Wunused-result] fscanf(fin,"%d",&mat[i][j]); ^~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c: In function 'backtrack': main.c:27:1: warning: control reaches end of non-void function [-Wreturn-type] } ^