12.010 Basic C: C and Fortran 77 Syntax
 
 

Declarations

C (statements end in ; all variables must be declared explcitly) F77 (start in column 7)
int a;       INTEGER A
float a;       REAL A
double a;       DOUBLE PRECISION A
char a;       CHARACTER A
short a;      
uint a;      
long int a;      
int a[10];      INTEGER A(10)
float a[10][10];      REAL A(10,10)
char a[10];      CHARACTER A(10)
char a[10];      CHARACTER A(10)

Simple Loop

C (array indices range 0 to N-1)F77 (array indices range 1 to N)
int i,j;
float arr[10][10];


for (j=0;j<10;++j){
  for (i=0;i<10;++i){
   arr[j][i]=1
  }
}
 		     INTEGER I
     INTEGER J
     REAL ARR(10,10)

      DO J=1,10
       DO I=1,10
        ARR(I,J)=1
       ENDDO
      ENDDO

C Hello World

#include <stdio.h>

main() {
  printf("Hello\n");            /* printf always goes to "standard output". */
  fprintf(stdout,"Hello\n");    /* fprintf goes to specified output stream  */
}

F77 Hello World

      PROGRAM MAIN
      WRITE(6,*) 'Hello'
      END

Formatting output

(see "man fprintf")

Integers

C
main() {

 int i;
 i = 7;

 printf("\n"); /* New line */
 printf("Leading blanks\n");
 printf("%1d\n",i);
 printf("%2d\n",i);
 printf("%3d\n",i);
 printf("%4d\n",i);
 printf("%5d\n",i);
 printf("%6d\n",i);

 printf("\n"); /* New line */
 printf("Leading zeros\n");
 printf("%1.1d\n",i);
 printf("%2.2d\n",i);
 printf("%3.3d\n",i);
 printf("%4.4d\n",i);
 printf("%5.5d\n",i);
 printf("%6.6d\n",i);
}
F77
      PROGRAM MAIN

      INTEGER I

      I=7

      WRITE(6,'(1X)')
      WRITE(6,'(A)')  'Leading blanks'
      WRITE(6,'(I1)') I
      WRITE(6,'(I2)') I
      WRITE(6,'(I3)') I
      WRITE(6,'(I4)') I
      WRITE(6,'(I5)') I
      WRITE(6,'(I6)') I

      WRITE(6,'(1X)')
      WRITE(6,'(A)')  'Leading zeros'
      WRITE(6,'(I1.1)') I
      WRITE(6,'(I2.2)') I
      WRITE(6,'(I3.3)') I
      WRITE(6,'(I4.4)') I
      WRITE(6,'(I5.5)') I
      WRITE(6,'(I6.6)') I

      END

Text

C
main() {

 printf("A");
 printf(" new");
 printf(" line");
 printf(" must");
 printf(" be");
 printf(" specified");
 printf(" explicitly.");
 printf("\n");

}
F77
      PROGRAM MAIN
       WRITE(6,'(A)') ' A new line is implicit in Fortran'
      END








Floating Point

C
main() {

  printf("%f",3.1459); printf("\n");
  printf("%f\n",3.1459);
  printf("%10.10f\n",3.1459);
  printf("%.10f\n",3.1459);
  printf("%10f\n",3.1459);
  printf("%10f\n",3.1459e12);
  printf("\n");

  printf("%e\n",3.1459);
  printf("%10.3e\n",3.1459);
  printf("%-10.3e\n",3.1459);
  printf("%+12.3e\n",3.1459);
  printf("%+-12.3e\n",3.1459);
  printf("%.10e\n",3.1459);
  printf("%10e\n",3.1459);
  printf("\n");

  printf("%E\n",3.1459);
  printf("%10.3E\n",3.1459);
  printf("%.10E\n",3.1459);
  printf("%10E\n",3.1459);
  printf("\n");

  printf("%g\n",3.1459);
  printf("%10.3g\n",3.1459);
  printf("%.10g\n",3.1459);
  printf("%10g\n",3.1459);
  printf("\n");

}
F77
      PROGRAM MAIN
      WRITE(6,'(F10.3)') 3.1459
      WRITE(6,'(E10.3)') 3.1459
      WRITE(6,'(E20.12)') 3.1459
      WRITE(6,'(1PE20.12)') 3.1459
      END

C Conditional


#include <stdio.h>
#include <errno.h>

main(){

  int i = 0;

  /* == returns logical result, proper conditional */
  if ( i == 0 ) {
    printf("test 1: i is set to %d\n",i);
  }

  /* Using = not == for equality tests is a common typing mistake in C    */
  /* Using = is valid syntax but it doesn't mean what you think it means! */
  /* i = 0 is false ( it returns 0 ) by definition, irrespective of the   */
  /* value of i.                                                          */
  if ( i = 0 ) {
    printf("test 2: i is set to %d\n",i);
  }

  /* i = 1 is true ( it returns non-zero ) by definition, irrespective of */
  /* the value of i.                                                      */
  if ( i = 1 ) {
    printf("test 3: i is set to %d\n",i);
  }

}

F77 Conditional

      PROGRAM MAIN

      INTEGER I

      I = 0

      IF ( I .EQ. 0 ) THEN
       WRITE(6,'(A,I4)') 'I is set to', I
      ENDIF

      END